Sustainability
briefings
A set of briefing sheets written by the Sustainable Construction Panel
Contents
Foreword
3
1
What is sustainability?
4
2
Capital vs lifecycle vs whole-life costs
6
3
What is embodied carbon?
7
4
How to carry out a carbon impact assessment of a structural consultancy office
8
5
Site waste management plans
10
6
Green roofs
11
7
Code for Sustainable Homes – how to win credits
13
8
The Copenhagen Accord
16
9
Responsible sourcing
19
10
CHP: a guide for structural engineers
20
11
Recycled and secondary aggregates in concrete
21
12
Carbon trading
24
13
The reuse of structural components and materials
27
14
Wales and its steps towards zero carbon buildings
29
15
Design for deconstruction
31
16
Sustainability for bridge engineers – Part 1
33
17
Sustainability for bridge engineers – Part 2
36
18
Cementitious materials
38
19
Climate change and wind speeds
40
Further information
These briefings were prepared by the Sustainable Construction Panel. Contact: Berenice Chan (email: [email protected]).
The sustainability area of the website (www.istructe.org/sustainability) includes links to useful websites arranged by category with brief
descriptions.
2 The Institution of Structural Engineers | Sustainability Briefings
Foreword
This document is a collection of briefing notes authored by The
Institution of Structural Engineers’ Sustainable Construction Panel
from 2008 to 2011. The briefing notes were peer reviewed and
discussed by the panel in order to achieve a broad consensus in
a developing area of expertise. The notes were regularly published
in The Structural Engineer. They provide guidance, opinion
and overview on emerging topics of relevance to sustainable
structures. We hope that this collection serves to illustrate the
variety of issues relevant to sustainability and supports Institution
members to navigate this complex field.
Knowledge and practice of sustainability is changing fast and this
may mean that some of the content in these notes falls out of
date quickly. Regardless of this the notes set out the principle of
the approach, even if some matters of detail change.
We hope you enjoy reading these notes and that they stimulate
discussion and ideas for more sustainable structural design and
construction.
Sarah Kaethner
Chair of Sustainable Construction Panel 2013
The Institution of Structural Engineers | Sustainability Briefings 3
What is sustainability?
Briefing Note 1
Prepared by the Sustainable Construction Panel, this is the first in a series of briefing sheets, which
will provide engineers with information and knowledge to help implement sustainable solutions.
The philosophical basis
The Structural Engineer 6 May 2008
Different people and organisations might have a range of views
on the definition of sustainability, which is commonly considered
to include a balance of environmental, social and financial
issues. The Natural Step for example (www.naturalstep.org)
uses the metaphor of a funnel to visualise economic, social
and environmental pressures putting pressure on society as
natural resources diminish and population grows. At its root,
sustainability demands that we understand and control the wider
impact of human activities for the benefit of future generations.
It can be helpful to draw a distinction between sustainable
development (the process, or journey), and sustainability (the aim,
or destination).
Environmental sustainability
The Earth’s resources are finite, and require careful management.
Pressures on environment include:
–– population growth
–– deterioration in land and soil
–– pollution of water
–– changing atmosphere (particularly in relation to greenhouse
gases)
–– reduction in bio-diversity
–– sea level and temperature change.
Key considerations include:
–– material use (including resource depletion)
–– depletion of fossil fuel reserves
–– water use (including resource depletion)
Former US Vice President turned environmental campaigner,
Al Gore, has been effective in demonstrating the scientific facts
of environmental damage caused by unsustainable living2. It is
recognised that environmental damage and climate change will
lead to conflict and social breakdown. In the UK, where action has
concentrated on climate change and reducing greenhouse gas
emissions, sustainability is a hot political issue.
Social sustainability
The ‘green’ agenda addresses the issue of affluence and
overconsumption. The so called ‘brown’ agenda focuses on
poverty and under development – the need to reduce the
environmental threats to health due to poor sanitary conditions,
crowding, inadequate water provision, hazardous air and water
pollution, and accumulations of solid waste.
In developed countries social sustainability frequently focuses on
social equity, cultural issues, traditions, heritage issues, health and
comfort, social infrastructure and a safe and healthy environment.
In developing countries the social focus shifts to poverty
reduction, job creation and access to safe, affordable and healthy
shelter. At the Johannesburg Earth Summit (2002), the three ‘P’s
were coined – ‘people, planet, prosperity’.
Corporate sustainability
Sustainability is often regarded as good for business. To control
costs, and demonstrate competence to their shareholders, many
commercial organisations are changing and promoting change
within their suppliers.
Drivers for change include politics and legislation, customer
pressure and achieving continued and increased profitability.
Some businesses have referred to the three P’s as ‘People, Planet
and Profit’.
–– emissions to air and water
Economic sustainability
–– embodied energy and energy in use
The Stern Review3 examined the economic effect of
environmental degradation on the economy, concluding that
“annual emissions of GHGs must be reduced to 80% below
current levels for stabilisation”. The UK Government’s economic
advisor, Lord Nicholas Stern, argued that “sustained long-term
action can achieve this at costs that are low in comparison to the
risks of not acting”. Without action, he estimated the overall costs
and risks of climate change will equate to a loss of at least 5% of
global GDP annually, however with immediate action, the costs of
reducing GHGs can be limited to about 1% GDP.
–– waste disposal.
Sustainability – political motivation
In 1987, the Bruntlandt report stated ‘Humanity has the ability
to make development sustainable —to ensure that it meets
the needs of the present without compromising the ability of
future generations to meet their own needs’1. Sustainability, and
specifically climate change, was introduced into the political arena
with the Kyoto Protocol in 1997 and has gained momentum
since.
4 The Institution of Structural Engineers | Sustainability Briefings
Sustainable construction
Construction has an impact on sustainability throughout its life
cycle. Sustainable construction can be a major force in redressing
the environmental balance. The late David Pearce4 defined the
construction industry’s contribution to sustainability as:
–– Manufactured capital – capital stock, construction and capital
formation, longevity of built wealth
–– Human capital – labour force, training and skills, productivity,
health and safety
–– Natural and social environment – materials balance,
energy balance, pollution, benefits of the built environment,
sustainable communities
–– Technological progress – improved productivity; research and
innovation, design and whole-life costing.
Sustainability for engineers
Engineers are implementing the changes needed for sustainability.
These include sustainable urban drainage systems (SUDS) and
sustainable energy generation. Issues of particular relevance to
structural engineers include:
–– enabling change of use
–– enabling refurbishment
–– design for safe construction and use
–– reusing and recycling materials
In 1999, the Institution report Building for a Sustainable Future5
was the first coherent study of the implementation of sustainable
construction. Still a highly relevant introduction, it has recently
been revised by an Institution Task Group. With the publication of
these briefing sheets, it is hoped the Institution can continue to
support engineers in this critically important field. Engineers can
have a direct impact through their design work and, by being well
informed, they can influence others in the design process.
References
1. Bruntlandt, G. H.: Report for the UN World Commission on
Environment & Development, Our Common Future, Oxford
University Press, 1987, ISBN 0-19-282080-X
2. Gore, A.: An inconvenient truth: The Planetary Emergency of
Global Warming and What We Can Do About It, Bloomsbury
Publishing plc 2006. Also an American Academy Awardwinning documentary film of the same name
3. The Stern Review Report: The economics of climate change,
HM Treasury, 2006
4. Pearce, D.: The social and economic value of construction,
the construction industry’s contribution to sustainable
development, A report for nCRISP the Construction Industry
Research and Innovation Strategy Panel, 2003
5. Building for a sustainable future – construction without
depletion, The Institution of Structural Engineers, November
1999
–– reduction of resources through intelligent design
–– selection of materials for low environmental impact
–– efficiency of material usage
–– design for long life and future flexibility
–– integrated design with architect and environmental engineer
–– design for de-construction.
Being dedicated to process, engineers have an advantage over
other professions. Their work moves logically from concept
through scheme design to construction and commissioning. For
cost control, the impact on design is considered stage by stage
and the same is possible for consideration of environmental
impact.
Sustainable development is a new and rapidly changing field.
The Institution of Structural Engineers | Sustainability Briefings 5
Capital vs lifecycle vs whole-life costs
Briefing Note 2
In construction, ‘cost’ is frequently defined by duration, the
most commonly used being capital cost (zero duration), where
only the initial cost at construction is taken into account without
consideration of subsequent maintenance or running costs.
However, there are two other methods of assessing cost, both of
which take into account maintenance or running costs which are
occasionally considered when assessing alternative options:
Lifecycle – a composite of capital cost of an element of building
plus maintenance (and occasionally, running) costs over a fixed
cycle, normally 2-10 years, rarely longer.
The Structural Engineer 17 June 2008
Whole-life costs – the total projected cost of a building (or
element of a building) over its whole design life, often 25-60 years,
including maintenance and elemental replacement costs.
The phrase ‘payback period’ is often used in context with
these alternative methodologies. This is the length of time that
the initially more expensive item takes to achieve cumulative
cost parity with the cheaper alternative as lower running or
maintenance costs keep the total cost of the more expensive item
down whilst reflecting the higher real costs associated with the
cheaper alternative. Shorter payback periods are obviously more
attractive than longer ones.
Running costs are normally only taken into account by owneroccupiers, but these are rarely considered beyond around five
years. Speculative developers rarely have an interest in anything
other than capital cost as they are not responsible for future costs
– potential owners are.
Why use cost comparisons other than capital?
Alternative cost comparisons can make the more ‘expensive’
option (in terms of capital cost) less costly in the longer term than
the alternative with the ‘cheaper’ capital cost, as this permits
future savings to be taken into account.
Cost
–– New products or technologies tend to be more expensive
than established alternatives until manufacturing volumes (i.e.
sales) have reached suitable levels to compete on price.
The value of this approach in the first of these two areas is quite
clear – alternative cost analyses allow purchasers to rationalise
the more expensive alternative against future benefits – pay a little
more now, but save overall in the longer term, often just a few
years.
It is in the second area however that cost comparisons other than
capital are of particular value. Clearly, a new product could have
great value to a customer, such as being exceptionally durable, or
offering real savings in running costs, and although in the longer
term manufacturing costs will reduce, today the product is more
expensive than alternatives. With the right customer, such as one
who wants a cutting-edge building, alternative cost comparisons
can make new technologies ‘affordable’ (or even unmissable), and
make them trend-setters in their sector.
To date, ‘cost’ has automatically been taken to mean ‘money’,
but the analysis methods are equally applicable to ‘carbon’ as a
unit of comparison.
–– Capital cost would be a comparison of the constructionphase carbon (energy) expended to create the building.
–– Life-cycle would be its construction, running and maintenance
carbon over an analysis period.
–– Whole-life would be construction, running and maintenance,
plus the recycling-carbon cost (or recovered-carbon credit) at
the end of its working life.
Perhaps in today’s progression to a carbon-lean economy, this is
the real potential benefit of alternatives to capital cost as the
measure of value – tools to help design teams to make truly
sustainable decisions? In this way, when considering, for example,
an energy-saving installation, the carbon payback period could be
established and taken into account together with financial
considerations.
Cost
Whole-life cost for Option 1
3
2
1
Disposal cost at EoL
Maintenance cost
End of
Life
Running cost
Capital cost
Payback period
Opt 2 vs Opt 1
2
Payback period
Opt 3 vs Opt 1
1
Time
Figure 1
Why is this type of comparison becoming more important?
There are two areas where such comparisons can help to justify a
decision to use a product with a higher capital cost:
–– Better quality, better performing, or more durable products
tend to be more expensive than basic alternative products
that perform less well (although by definition, meet
the specification), or will require earlier or more costly
maintenance, or even replacement.
6 The Institution of Structural Engineers | Sustainability Briefings
Recovery value at EoL
Whole-life cost for Option 2
Time
Figure 2
What is embodied carbon?
–– Management carbon (Mc): the off-site cost of managing the
delivery of a project – customer, consultants, contractor, etc.
–– Embodied carbon in materials (Ec): the carbon impact of the
extraction, production and assembly of the raw materials and
components of a project.
–– Construction carbon (Cc): the carbon input required to
assemble the building on site.
–– Deconstruction carbon (Dc): the impact of taking apart the
building at the end of its life, and recovering materials for reuse
or recycling, landfilling or other disposal.
Of the total (the whole life carbon, WLc), embodied carbon (Ec),
and operating carbon (Oc) are the two major contributors. At
present, the focus is on reducing operating emissions (‘zerocarbon buildings’), an area in which the structural engineer can
make some contribution, but which is primarily driven by other
members of the design team. However, the frame and envelope
of the building contain a relatively large proportion of the project’s
embodied carbon, and it is in this area that the structural engineer
can make a significant impact, particularly as reductions in
operating emissions become harder to achieve.
But what is ‘embodied carbon’, and how do you calculate it?
Embodied carbon is quite simply the carbon dioxide emissions1
generated in producing the materials that are used in the
construction process, from the obvious elements such as steel,
timber, masonry, cement and aggregates, through to the more
complex constructions and systems such as a window unit, or
a complete air conditioning unit. These emissions are not only
from the sourcing of the raw materials from the earth and their
conversion into a usable form, but also from the energy used
whenever work is done on them, for example the fabrication of
raw steel sections into the individual members of a steel frame.
Transportation
But then there is the issue of transportation – how should you
compare a product shipped halfway around the world in a
container to a similar item road-hauled from Europe? And what
about the waste generated in its manufacture? Is this part of the
product’s ‘carbon footprint’, or does it belong to something else?
And when you are calculating the carbon impact of the energy
used in any process, should you use national averages, or the
actual energy impact at the plant? For example, a manufacturing
company may have signed up to a green energy tariff or use
energy from a renewable source – should products from this plant
have a lower carbon footprint than those from another plant that
does not use ‘green energy’? There are many similar questions.
But how much better would it be if everyone worked to a
common standard?
And therein lies the current problem – there is no single standard
or methodology in place today that is broadly recognised as being
the ‘right way’ to calculate embodied carbon, although many
trade and industry bodies are working on potential solutions.
One of these is a new industry specification (PAS 2050) which is
currently being developed by BSI, which builds upon the original
methodology proposed by the Carbon Trust. When this (or
another standard) becomes broadly accepted within the industry
and a set of industry-average figures for construction materials
is derived using it, the way is then open for structural engineers
to make informed decisions on the relative merits of alternative
solutions, not only on the basis of structural performance, but
also on carbon impact, and to actively consider this as part of the
design process.
Detailed specification
The next stage would be to take this way of thinking into detailed
specification. If everyone calculates embodied carbon to the same
standard, then as you move away from the generic analysis at
the start of a project into detail design and specification as the
project progresses, there is the opportunity to confidently specify
a particular manufacturer’s products with a lower declared carbon
footprint, knowing that you will be further lowering the overall
carbon impact of the design.
Role for structural engineers
By recognising and reducing the carbon emissions to the
atmosphere associated with the initial construction of the project,
and hopefully mirroring the efforts that are being made by other
members of the design team to reduce the operational carbon
emissions during the life of the building, structural engineers can
play an important role in the achievement of genuinely low carbon
construction over the whole life of the building – in construction as
well as in use.
1. Carbon dioxide emissions are frequently referred to as ‘carbon dioxide
equivalent’ or ‘CO2e’, as other gases as well as carbon dioxide cause
greenhouse effects. For example, methane is 23 times more potent in terms
of greenhouse effect, so 1t of methane is considered to be the equivalent of
23t of carbon dioxide. To avoid having to refer to each of the gases individually,
the effect of the various gases given off during any process is normalised to
their ‘carbon dioxide equivalent’ (CO2e), and just the single unit used for any
calculations.
Further reading
Smith, B. P. ‘Whole-life carbon footprinting’ The Structural
Engineer 86/6, 18 March 2008 p.15/16.
Methodology
Much of the methodology of carbon footprinting is drawn from
the discipline of life cycle analysis (LCA), where these issues are
referred to as ‘boundaries’. It is essential to know and understand
the boundaries that have been assumed for any declared carbon
footprint as this tells you what is included – and what has been
left out. So can you compare the carbon footprint calculated to
one set of boundaries for one product, to the footprint of another
calculated to a different set of boundaries? Yes you can, but only
The Institution of Structural Engineers | Sustainability Briefings 7
The Structural Engineer 19 August 2008
–– Operating carbon (Oc): the cost of operating and maintaining
the building through its working life.
by working with your supply chain to understand the boundaries
used.
Briefing Note 3
The five main areas of greenhouse gas impact from a typical
building project are:
What it is
A carbon footprint is a measure of the different environmental
impacts of human activities, in terms of CO2 produced. A carbon
footprint measurement of this type is known as a Carbon Impact
Assessment. To evaluate carbon footprint correctly, it is important to
assess all impacts together. For an office-based company, all office
and transport activities must be considered. An office may have an
‘excellent’ BREEAM rating but its impacts from ‘transport’ are likely to
be far more significant than those from running the ‘office’. These
What itare
is more widely explained in the next paragraphs.
inputs
2. Indirect emissions from generation of purchased electricity, heat,
steam.
3. Indirect emissions not directly controlled from business travel in noncompany owned vehicles, employee commuting in vehicles not owned
by company (e.g. light rail, train, buses, employee cars).
How to carry out a carbon impact assessment of a
structural consultancy office
items
to bethat
included:
Activities
create a carbon footprint include:
• Bills for heating, gas and electricity (heat, A/C, lights, computers,
––printing,
Transport
etc.)
• Quantities of water, paper, printing, stationary,
–– Heating and air-conditioning
• Transport (distances travelled)
can (plug
be gathered
––Information
Small power
loads) from company bills and company
records. To calculate the carbon footprint of a company, much of the
–– Lighting
work
can be done by one or two people but the involvement of every
individual
is important
to raise awareness
and encourage
–– Production
and consumption
of products
and the people
energyto
consider
their in
own
contribution.
involved
their
manufacture (use) and disposal.
Measurement of carbon footprint
What is measurable is manageable
When making a carbon impact assessment, these are some of
Once the carbon footprint is known, it is then possible to identify ways to
the items to be included:
reduce the carbon footprint. Every contribution to a carbon footprint is a
–– Bills
for heating,
gas or
and
electricity
(heat, A/C,
lights, money. An
result
of spending
money,
has
the consequence
of costing
computers,
printing,
etc.).
important
benefit of
analysing
carbon footprint is that data can be used
as a way of identifying unnecessary expenditure.
–– Quantities of water, paper, printing, stationary.
–– Transport
(distances
Calculating
carbon
footprinttravelled).
There
are many
calculators
(see
below) for
determining
Information
canonline
be gathered
from
company
billshelp
andincompany
carbon
footprint.
Most ofthe
them,
however,
are of
aimed
at an individuals’
records.
To calculate
carbon
footprint
a company,
much of
carbon
footprint
(housing,
the work
can be
done bytravelling).
one or two people but the involvement
of every individual is important to raise awareness and encourage
people footprint
to consider
their own
contribution.
Carbon
assessment
data
according to Reference 1 should
by divided into three groups:
What
is emissions
measurable
is of
manageable
1.
Direct
(use
fuel, electricity, steam, heat in the
appliances
directly
owned
by
business
Once the carbon footprint isreporting
known, organisation,
it is then possible
to travel
and
employee
commuting
in
company
owned
vehicles).
identify ways to reduce the carbon footprint. Every contribution
to a carbon footprint is a result of spending money, or has the
consequence of costing money. An important benefit of analysing
carbon footprint is that data can be used as a way of identifying
12
The Structural
Engineer 7 October 2008
unnecessary
expenditure.
Calculating carbon footprint
There are many online calculators (see below) for help in
determining carbon footprint. Most of them, however, are aimed
at an individuals’ carbon footprint (housing, travelling).
Carbon footprint assessment data according to Reference 1
should by divided into three groups:
1. Direct emissions (use of fuel, electricity, steam, heat in the
appliances directly owned by reporting organisation, business
travel and employee commuting in company owned vehicles).
2. Indirect emissions from generation of purchased electricity,
heat, steam.
3. Indirect emissions not directly controlled from business travel
in non-company owned vehicles, employee commuting in
vehicles not owned by company (e.g. light rail, train, buses,
employee cars).
8 The Institution of Structural Engineers | Sustainability Briefings
http://actonco2.direct.gov.uk/index.html
DEFRA’s
calculator website. Compares users’ footprint to the
DEFRA’s
calculator
website.
Compares
users’
footprint
theofUK
UK statistical
average.
It provides
an action
plan
with atolist
statistical
average.
It
provides
an
Action
Plan
with
a
list
of
personalised recommendations about how to reduce carbon
personalised recommendations about how to reduce carbon
emissions.
emissions.
Online calculators
Online calculators
http://www.carbonfootprint.com/calculator.aspx
http://www.carbonfootprint.com/calculator.aspx
This
small businesses
businessesless
lessthan
than
Thisrequires
requiresaafree
freeregistration
registration for
for small
20
youwill
willbe
becontacted.
contacted.
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20staff.
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Forlarger
larger companies
companies you
Data
used
used
includes
emissions
housing,
travel
and secondary
includes
emissions
from; from:
housing,
travel and
secondary
consumptions
shopping,recycling,
recycling,etc.).
etc.).
consumptions (food,
(food, shopping,
http://www.carbontrust.com
http://www.carbontrust.co.uk/default.ct
Carbon footprint calculator also for companies after registration.
Carbon footprint calculator also for companies after registration.
Required data are: fuel usage (gas bill), vehicle usage, electricity
Required data are; fuel usage (gas bill), vehicle usage,
bills and employee travel details.
electricity bills and employee travel details.
http://www.carboncalculator.co.uk/
http://www.carboncalculator.co.uk/
Requires
registration. Data from travel, heating, electricity and
Requires are
registration.
shopping
required.Data from travel, heating, electricity and
shopping are required.
Mauna Loa Observatory, Hawaii
Monthly Average Carbon Dioxide Concentration
Data from
Scripps
Program LastHawaii
updated July 2008
Mauna
LoaCO
Observatory,
Monthly Average Carbon Dioxide Concentration
390
Data from Scripps CO Program Last updated July 2008
2
380
12 The Structural Engineer 7 October 2008
370
360
350
340
2
The Structural Engineer 7 October 2008
its impacts from ‘transport’ are likely to be far more significant
than those from
running
the ‘office’. These inputs are more widely
Measurement
of carbon
footprint
explained
in theanext
paragraphs.
When making
Carbon
Impact Assessment, these are some of the
http://actonco2.direct.gov.uk/index.html
CO Concentration (ppm)
Briefing Note 4
A carbon footprint is a measure of the different environmental
Activities
that
createactivities,
a carboninfootprint
include:
impacts of
human
terms of
CO2 produced. A carbon
•footprint
Transport
measurement of this type is known as a carbon impact
•assessment.
Heating and To
Air-conditioning
evaluate carbon footprint correctly, it is important
•to
Small
power
(plug loads)
assess
all impacts
together. For an office-based company,
•all
Lighting
office and transport activities must be considered. An office
•may
Production
consumption
of products
the energy
have anand
‘excellent’
Building
Researchand
Establishment
involved in their
manufacture
(use) and disposal.
Environmental
Assessment
Methodology
(BREEAM) rating but
http://www.defra.gov.uk/environment/business/envrp/pdf/conve rsionfactors.pdfGuidelines to DEFRA’s GHG (greenhouse gas) conversion
factors.
330
320
310
1960
1965
1970
1975
1980
1985
Year
1990
1995
2000
2005
The graph shows increased carbon dioxide concentration from
1960 already measured at Manua Loa Observatory, Hawaii.
(Scripps Institution of Oceanography).
2010
Manua Loa Observatory is the premier long-term atmospheric
monitoring facility on earth and is the site where the everincreasing concentrations of global atmospheric carbon dioxide
have been determined. Due to its mid-Pacific location it is not
close to significant sources of carbon production. This means that
the readings are an acceptable average for the rest of the planet.
For more information see website: http://scrippsco2.ucsd.edu
Reducing carbon footprint in the office
The necessary steps for reducing carbon footprint are as follows:
1. Nominate a person, with senior management support,
responsible for CO2 reduction plan.
2. Learn what data are required and how to collect them.
3. Calculate office’s carbon footprint by using one of the carbon
footprint calculators.
4. Find out how to reduce carbon footprint and action.
5. To secure consistency, check carbon emissions regularly, by
using exactly the same carbon footprinting methods.
References
1. Putt del Pino, S., Bhatia, P.: Working 9 to 5 on Climate
Change: An Office Guide, World Resources Institute,
December 2002
The Institution of Structural Engineers | Sustainability Briefings 9
Site waste management plans
Briefing Note 5
The Site Waste Management Plan Regulations 2008 (SWMP
2008) came into force in England and Wales on 6 April 2008
and seeks to achieve a reduction in illegal fly-tipping, and to
reduce the quantity of construction waste that is sent to landfill.
This legislation applies to all projects with a contract value over
£300000, and whilst it places responsibilities on both the client
and main contractor, there are aspects that may affect the
structural engineer whether working on site or in the design office.
The Structural Engineer 4 November 2008
The first of these issues, reinforcement of the duty of care
legislation to require project teams to prove that they have
checked that any waste contractors used are properly licensed
and are using appropriately licensed disposal sites, is intended
to reduce the risk of flytipping, and will have little impact on
structural engineers unless they are responsible for waste disposal
operations on site.
However, in the area of waste management on site, and in
particular waste minimisation during design, structural engineers
can contribute on virtually any project. To put this into context, it is
necessary to understand the impact of waste in the construction
process.
The waste issue and the true cost of waste
According to national statistics (Environment in your Pocket,
2006), the UK generated 335Mt of waste, of which 32% (107Mt)
was from the construction and demolition industry, the largest
contribution from any industry sector, including mining and
quarrying, or agriculture. At the same time the construction and
demolition sector contributed 11% of the UK’s GDP, so our
sector’s waste is disproportionate to its value to the economy.
On a typical project, the cost of waste disposal is roughly
0.3–0.5% of a project’s value, and it should be remembered that
waste is not just the content of skips, but also other materials
that may be removed by trade contractors, such as earthworks,
excavation arisings, or hazardous wastes. However, recent
studies have shown that the cost of purchasing the materials
thrown away in skips is roughly 10 to 20 times the cost of their
disposal, so the true cost of ‘waste’ is probably 3–10% of
the project value. Clearly minimising waste during design can
therefore have a significant impact on project cost, and its viability.
Within the SWMP 2008, whilst the focus is on reducing waste
sent to landfill through recovery and recycling during construction
operations, there is the opportunity to commence site waste
management planning and waste minimisation during design,
gaining not only reduced disposal costs, but also the 10-20×
implied cost savings through reducing the need to purchase
excess materials.
A practical approach
Regarding planning, it may be worth considering at an early stage
how the site could be organised during construction, and how the
main contractor may operate: Where will the waste be stored?
How much space is available for recycling? Is there a suitable
space to store materials deliveries to minimise the risk of damage
(and consequent waste)? Might making additional space available,
even temporarily, actually reduce the cost of the project? By
10 The Institution of Structural Engineers | Sustainability Briefings
considering these issues early, substantial improvements in waste
management could be realised during the construction stage. And
there is no reason why the structural engineer should not be the
one to raise these issues.
Prefabrication and off-site construction
Another issue that must obviously be considered is that of
prefabrication or off-site construction. Whilst it is easy to dismiss
this as merely transferring the waste to another location, factorybased fabrication can significantly reduce overall waste. Behind
this is an understanding that off-site manufacture typically
specialises in one particular construction, and as such is able
to maximise materials use and minimise waste, for example by
using parts of the same stock sheet for components for different
projects that are in the works at the same time. In comparison,
the same work done on site does not permit the use of such
offcuts on other projects, and these automatically become waste.
Equally, off-site manufacturing plants are set up to recycle many
of the component materials they use, either internally (in the case
of the precast concrete industry), or externally (in the case of steel
fabrication), resulting in a far higher recovery and recycling rate
than would be achieved if the same operations were carried out
on site.
But behind this must also be considered the issue of transit
packaging: Does the completed fabrication now require so much
temporary protection that the waste generated by throwing this
away on site is greater than that from doing the work on site in
the first place? How could this be improved through reusable
protection, and how willing is the off-site fabricator to adopt
this approach to minimise overall waste? How many engineers
consider these questions during design?
Sourcing materials
Beyond this are some more mundane considerations. How often
when specifying components do we consider pack sizes, or
board widths and lengths, or whether materials will be obtained
locally or imported some distance, or are on long delivery
periods? These latter points are of surprising importance – when
materials are hard to come by for any reason, the temptation is
to over-order ‘just in case’, whilst where materials or components
are freely available locally, contractors’ will happily buy ‘tight’, safe
in the knowledge that they can pop out and pick up a few more
if they need them without risking delays. It is always useful to
recognise a very simple fact:
Accurate quantities + over-order = building + skips
Not exactly a ground-breaking revelation – but you can only put
so much material into a building, and anything that’s left over often
goes into the skips – especially if it’s project-specific and can’t be
readily reused elsewhere. So reducing the temptation to overorder can reduce waste, and in these days of carbon-sensitivity,
it’s worth remembering that anything manufactured just to throw
away wastes carbon, so minimising waste also contributes to
low-carbon construction.
Green roofs
What they are
Thickness (mm) Weight
(kg/m2)
Plants
20-100
30-80
Saturated growing medium
30-150
30-200
Root barrier / filter
3
3
Why use them
Drainage layer
50-60
3-10
The primary reason for installing a green roof on a project is
to increase bio-diversity for the site. This reduces the negative
ecological impact of a project, and increases the points available
on the BREEAM environmental scoring system. There are other
benefits, which include good thermal performance, good sound
insulation, air filtration, rain runoff reduction and attenuation.
Waterproof membrane
4-5
4-5
Insulation (warm roof)
50-150
3-10
Vapour control layer
3
3
Extensive and intensive roofs
Roofs fall into two categories:
Extensive roofs consist of a relatively shallow growing medium
and are intended to be low maintenance, once planted they
are left to grow except for occasional maintenance and are not
intended for general access or recreation.
Intensive roofs require a deeper layer of soil, up to 450mm, and
are more of an amenity or ‘roof garden’. These roofs may include
features such as lawns, flower borders or ponds. The additional
weight of this planting has greater structural implications.
Brown roofs are a specific form of extensive green roof where
locally sourced materials are laid on the roof. The roof is then
typically left to self colonise with indigenous plants and insects.
This briefing note concentrates on extensive green roofs.
Make up
Roofs can be either insulated or un-insulated depending on the
requirements of the building. See Figure 1 for the constituent
parts. The most important layer is the waterproofing. This can
take various forms:
–– A membrane that is rolled out and welded along the seams.
–– A hot-melt system that is poured on and spread out over the
roof.
–– Panelling system that is joined at the edges.
Some of the manufacturers of membranes include: Sarnafil,
Bauder (membranes), Alcan Falzonal, Corus Kalzip (standing
seams), Permaquick (hot melt system) and Kingspan (composite
panels).
On top of the waterproof membrane is a drainage layer / moisture
reservoir and a growing medium in which the plants are planted.
The growing medium is similar to topsoil in its function, but the
constituents are designed to be more absorptive than regular
topsoil (Figure 4).
Loading
The total weight of the systems can vary between 70-310kg/m2
or 0.7-3.1kN/m2. Typically a greater depth of growing medium will
increase the biodiversity potential of the roof. This will influence the
points available under the BREEAM rating system.
Table 1
Cost
Costs will vary according to specific requirements for the roof
geometry and plants required. Typically the supporting structure
may need to be stronger to carry the extra load depending on the
depth of growing medium used. As a running cost there will need
to be maintenance, but there will be savings from the increased
thermal performance.
Installation
The rate of installation of a green roof depends very much upon
the complexity of the shape of it. All systems can be installed
more quickly over large flat areas, and will take more time
where lots of corners and details have to be accommodated. A
waterproofing membrane may be laid at 10 to 50 to 150m2/day
for a team of two – depending on the amount of detailing that is to
be incorporated and whether it is a large flat roof.
Details
Pitch / gradient – 1:60 to 1:80 for ‘flat roofs’ – up to 20° roof
pitch is fairly standard application. Above this pitch complexity
(and cost) increases as measures need to be taken to ensure
the growing medium does not slip down the gradient. In certain
situations green roofs can be laid without a gradient.
Lightning protection – Surface mounted should be achievable but
confirm with manufacturer.
– Perimeter mounted or mounted over green roof by way of
mounting blocks placed on planted element surface.
Fall protection – Needs to be fixed through the waterproofing layer
and back to the structure.
Edge protection – Needs to be fixed back to the structure.
Parapet details – Must ensure continuity of waterproofing.
Rain outlets / overflows – Check with manufacturer if these are
off the shelf, bespoke manufacturer off site with lead in times, or
made on site. It is important that these are maintained and kept
clear to prevent flooding of the roof which could potentially cause
structural overloading.
Thermal performance – There is opportunity to tailor the amount
of insulation installed and achieve very good U values – 150mm
of foam glass insulation is typically enough on a membrane type
roof. Manufacturers of different types of insulation will be able to
provide specific data on thermal performance. Parapets need
The Institution of Structural Engineers | Sustainability Briefings 11
The Structural Engineer 87 (1) 6 January 2009
Material
The term ‘green roof’ is a generic name for a roof of a structure
that has some variety of plants installed on it. Traditionally grass
has been installed on pitched roofs in agricultural environments,
but more commonly for urban locations the ‘sedum’ species of
plant or roof gardens are installed on flat roofs.
Briefing Note 6
Guidance on what green roofs are, why use them and how they are constructed
Figure 1 Constituent parts of a green roof
Figure 2 Application of vapour control layer
Figure 4 Growing medium being added
to be designed accordingly to avoid cold bridging. The growing
medium has a tendency to contribute to thermal lag, keeping
the building warm at night and reducing heat build up from solar
radiation by day.
Rain attenuation and runoff reduction – The storage capacity
of the drainage layer and the growing membrane affects the
rain water runoff in two ways. Firstly there is an attenuation
effect, whereby the maximum runoff occurs after a greater delay
than for a smooth roof, this can reduce the maximum capacity
requirement of the drainage system. The second effect of a green
roof is that not all of the water runs off the roof. For a nominally flat
roof in the region of only a quarter to a third of the annual rain that
lands on the roof may run off into the drains. It must be verified
that the weight of the roof system quoted by the manufacturer is
based on saturated figures. Attenuation and runoff reduction is
most pronounced for roofs that are nominally flat.
Sound insulation – Green roofs are good at reducing noise
transmission into the building. The plants contribute to absorbing
high frequency sounds and the soil and lower layers absorb low
frequency sounds.
Time to settle in
A grass roof can be green from the day it is planted if pre-grown
turf is used, but this will be more susceptible to dry spells, require
back up irrigation and deeper layers of growing medium. Sedums
take approximately a year to fully take root (see Figure 5) and
do not require irrigation provided they are not installed in midsummer. For non-sedum varieties of plants a backup irrigation
system may be installed.
Pre-grown sedum mats are available and can provide almost total
cover at completion of installation. Alternatively an onsite planted
option will improve the creation of habitat and diversity of planted
species either using seeds or plug in plants.
12 The Institution of Structural Engineers | Sustainability Briefings
Figure 3 Reservoir layer installation in progress
Figure 5 Green roof one year after installation
Sedum roofs are low maintenance but not ‘no maintenance’.
It is important to ensure that drainage and overflow points are
kept clear and plants do not encroach on exclusion zones or fire
strips around the perimeter. Periodic addition of fertiliser will also
help maintain the biodiversity. Clients may choose to engage in a
periodic maintenance contract to ensure the roof is kept in good
order.
Wind loading performance
The roof is similar to that of a ballasted roof in that it has loose
parts (typically the stones to the perimeter). Plants may be blown
away initially, or pecked out by birds, but once the plants have
taken root the growing medium is knitted together.
Guarantees
As with all other roofs, green roofs need to keep all the water
out. It is strongly advised that all manufacturers and contractors
provide adequate guarantees and carry sufficient insurance
to cover repairs. An established quality assurance regime is
also recommended. As an example the Sarnafil system is both
visually inspected and also electronically tested to check for any
potential leakage sites. Typical guarantees available range from
15-25 years. However, due to the plants and soil protecting the
waterproof membrane from sunlight, the membrane does not
suffer degradation from UV radiation.
Reference
R Chudley and R Greeno, Building Construction
Handbook, Butterworth-Heinemann Ltd Acknowledgement:
Blackdown Horticultural Consultants www.greenroof.co.uk
Bibliography
www.bauder.co.uk
Code for Sustainable Homes – how to win credits
Background
In 1997 the UK committed to reduce its carbon emissions by
signing the Kyoto Protocol. Various assessment methods have
since been introduced to assist design teams in reducing the
impact of the built environment from concept to demolition.
Ecohomes methodology was superseded by the Code for
Sustainable Homes (CSH)1 for new domestic properties in
October 2007. However, Ecohomes continues to be used to
assess existing homes. Assessments are carried out by a CSH
assessor who has been trained to monitor the environmental
performance of the buildings.
Code Level
Minimum percentage reduction in dwelling
emission rate over target emission rate
Level 1 (*)
10
Level 2 (**)
18
Level 3 (***)
25
Level 4 (****)
44
Level 5 (*****)
100
Level 6 (******)
‘Zero Carbon Home’
Table 1.3 Code Levels for Mandatory Maximum Standards in Indoor Water
Consumption
Code Level
Maximum indoor water consumption (litres
per person per day)
Level 1 (*)
120
The CSH is a design guide, which was produced with the aim
of helping UK housing developments to achieve zero carbon
emission levels by 2016. In terms of energy performance, a ‘Level
1’ home corresponds to basic UK Building Regulations Part L
compliance, ‘Level 4’ is a Passivhaus3 standard and ‘Level 6’
represents a zero carbon development.
Level 2 (**)
120
Level 3 (***)
105
Level 4 (****)
105
Level 5 (*****)
80
Currently, use of the CSH is compulsory in the design of social
housing, which must achieve a minimum of code Level 3 or 4 by
2010, Level 5 by 2013 and Level 6 / zero carbon by 2016. The
CSH is divided up into nine categories:
Level 6 (******)
80
Table 1.2 Code Levels for Mandatory Minimum Standards in CO2 Emissions
Structural engineers can readily make a beneficial impact in four
of these categories, namely: energy and CO2 emissions, materials,
surface water run-off, and waste, discussed in more depth below.
–– Energy and CO2 emissions
–– Pollution
–– Water
–– Health and wellbeing
–– Materials
–– Management
Energy and carbon dioxide (CO2) emissions
–– Surface water run-off
–– Ecology
Energy and CO2 performance is weighted heavily in the
assessment, and credits rely partly on the performance and
thermal properties of the building fabric to reduce carbon
emissions. This is demonstrated by the percentage improvement
of the Dwelling Emissions Rate (DER) over the Target Emissions
Rate (TER).
–– Waste
The calculation is known as a Standard Assessment Procedure
(SAP) which focuses on insulation and heating system
performance. The SAP calculation needs an insulation value for
the building fabric (U value), which is determined by the material
used in the structure and construction as a whole*. There are
alternative, more rigorous methods, which involve further building
physics and dynamic modelling. These can lead to a better
assessment of overall energy performance.
* Consider the Green Guide for Specification5, which rates the construction
thermally and ecologically, at structural design concept stage
Figure 1 Kingspan Offsite
Lighthouse built to the Code for
Sustainable Homes at the BRE
Innovation Park (Photo courtesy
BRE)
The Institution of Structural Engineers | Sustainability Briefings 13
The Structural Engineer 87 (4) 17 February 2009
The building of domestic properties constitutes a major portion of
UK construction sector activity, and as such was seen as a main
target area for improvement. The Building Research Establishment
(BRE) Ecohomes environmental assessment methodology was
introduced accordingly. More recently the BRE has investigated
the environmental impacts in homes and schools by building an
innovation park at BRE Watford (Figure 1). More information on
the research is discussed in the BRE Information Papers IP 9/08
Parts 1 to 42.
The following tables, from the Technical Guidance4 to the Code,
summarise some of the code requirements.
Briefing Note 7
How the BRE’s Code for Sustainable Homes enables structural engineers to make a positive impact
on the reduction of a building’s ecological footprint
Easy credit wins:
–– Use insulating materials which have a low U value. Logically,
this should increase the percentage of improvement of the
DER, therefore improving energy performance.
–– The more efficient the thermal envelope and airtight the
construction, the more the operational energy demand is
reduced.
–– Integrated design between the structural engineer, architect
and building service engineer to create a building fabric which
moderates the internal environment and reduces energy
demand.
–– These factors all improve the efficiency of the overall building
performance, which is recorded on the building’s Energy
Performance Certificate (EPC). This forms a critical piece of
information in the building’s Home Information Pack (HIP).
Materials
‘Reduce, Re-use, Recycle’ – the structural engineer’s prerogative!
Credits can be gained through the re-use of building materials,
retention of building façades and the refurbishment of existing
building structures, rather than their demolition and replacement
with new.
However, the question must be asked ‘how do we do this
responsibly?’ Material specification should consider embodied
energy content, which is the energy used in sourcing the
construction materials, processing them, delivering them to site
and incorporating them in the construction. Environmental impact
ratings of various typical construction build-ups are provided
in the BRE’s Green Guide for Specification5 in which materials
and constructions are rated from A* to E on their environmental
impacts.
Easy credit wins:
–– Source 80% of materials responsibly. If timber construction is
adopted it must be 100% responsibly sourced – FSC, PEFC
registered.
–– Specify where possible A-rated constructions for the roof,
external walls, internal walls, upper and ground floors and
windows.
–– Structural design specifications should be reviewed and
optimised for incorporation of the use of materials such as
recycled aggregates.
–– Design for demolition: recycling of materials at the end of the
building’s life cycle should also be considered.
For further guidance on the relative environmental performance
of different typical constructions, look at the Green Guide for
Specification5 and work closely with the project’s CSH assessor to
use the material calculators to maximise the credits awarded.
All these points need consideration, the thought process
recorded, and made auditable for credits to be awarded. Your
CSH assessor should be able to advise you appropriately.
Water and surface water run-off
Water is a natural resource, fundamental for all life, which when
altered unsympathetically can result in flash floods, disease
and damage, therefore financial cost. This section is mandatory
and awards credits for the reduction of a household’s water
14 The Institution of Structural Engineers | Sustainability Briefings
consumption and for the reduction of surface water run off. It is
also a section that requires engineering to meet the targets, which
for domestic water consumption are:
–– Level 5 and Level 6: 80 litres/person/day.
–– Level 3 and Level 4: 90 litres/person/day.
–– Level 1 and Level 2: 120 litres/person/day.
Easy credit wins:
–– Specification of water saving devices: taps, low flush toilets,
rainwater harvesting and/or greywater recycling.
–– Storage and treatment plant to facilitate the above may have
some impact on the building layout and structure.
It is important to minimise surface water run-off as this can
help reduce flood risk, but it also reduces the amount of water
discharged into surface water drainage systems, thus helping to
minimise infrastructure costs. For sites in areas designated as
high flood risk, credits can only be awarded if 100% of surface
water flows are discharged through an attenuated system. Refer
to the CIRIA Interim Codes of Practice6 for Sustainable Drainage
and Planning Policy Statement 25 – Development and Flood Risk
(PPS 25) for further guidance.
Easy credit wins:
–– Sustainable urban drainage systems (SUDS)
–– ‘Green’ roofs
–– Attenuation of surface water.
Evidence is required for credits to be awarded, including
calculations for retention and attenuation systems, flood risk
assessments, drawings and correspondence confirming that
appropriate authorities have been consulted.
Waste
The UK construction industry uses 400M/t of materials every
year. Currently only 90M/t are recycled, of which 45M/t become
recycled aggregates. It is the UK Government’s objective by 2012
to have reduced the waste from construction, demolition and
excavation that goes to landfill by 50%. Landfill taxes continue to
rise and will be £48/t by 2010.
Through responsible specification and careful design, structural
engineers can minimise the disposal of waste to landfill, and thus
demonstrate that through their involvement, project costs can be
reduced.
What CSH doesn’t cover, but where you can have a significant
impact…
‘It is essential that we build the potential for adaption into design
and construction methods – whether this is a new development,
refurbishment or regeneration’7.
Structural engineers can play a significant role in reducing the
impact of climate change and depletion of natural resources, not
only through compliance with the Code for Sustainable Homes,
but also through doing what we do best – minimising costs by
using resources efficiently, solving problems interactively within
design teams, having the knowledge and skills to assess and
adapt existing buildings, and through bringing an open-minded
and innovative approach to design.
References
1. The Code for Sustainable Homes: Setting the standard
in sustainability for new homes, CLG, London. Feb
2008, see website: http://webarchive.nationalarchives.
gov.uk/20120919132719/http://www.communities.
gov.uk/documents/planningandbuilding/pdf/
codesustainhomesstandard.pdf
2. Applying the Code for Sustainable Homes on the BRE
Innovation Park (4-part set) Lessons learnt, C. Gaze et al, Oct
2008, BRE
3. Passivhaus, see website: www.passivhaus.org.uk
4. Code for Sustainable homes: Technical Guidance, Oct 2008,
CLG, London (http://www.planningportal.gov.uk/uploads/
code_for_sustainable_homes_techguide.pdf)
5. BRE Green Guide for Specification (www.thegreenguide.org.uk)
6. Interim Codes of Practice for Sustainable Drainage Systems,
National SUDS Working Group, July 2004.
7. Strategy for sustainable construction, BERR report, ch 9, p37,
June 2008 available on-line at: http://www.berr.gov.uk/files/
file46535.pdf
Bibliography
See UK government website: http://www.communities.gov.uk/
planningandbuilding/buildingregulations/legislation/englandwales/
codesustainable/
The Institution of Structural Engineers | Sustainability Briefings 15
The Copenhagen Accord
Briefing Note 8
Has the Copenhagen Accord, agreed at the COP 15 conference, made a difference to the debate
on climate change, and what does it mean for construction?
Introduction
The Structural Engineer 88 (2) 19 January 2010
In October 2009, Keith Clarke (Chairman, Construction Industry
Council), in his presentation to the Institution’s Council, made
a convincing argument for tackling climate change through
control of the carbon emissions. As a result many people in the
Institution will have been following progress of the climate change
negotiations in Copenhagen in December 2009.
Graham Owens, in his role as President of the Institution, took a
strong lead on establishing the importance of structural engineers
in their role in enabling construction to reduce its carbon
emissions. Both the ICE and the RIBA have argued for a ‘rational
legally binding global framework’ to emissions agreements.
This note provides the general reader with information on the
background to the Copenhagen meeting and summarises the
outcome.
The agreement at Copenhagen (The Copenhagen Accord) was
not the legally binding commitment to reduced emissions that
many had expected and there were political reasons for this.
Carbon reduction is still a live issue and, despite the outcome of
Copenhagen, engineers should expect that many of their clients
will call upon engineers to use skill and knowledge to produce
low-carbon construction solutions.
Background to the Copenhagen meeting
In Rio (1992), at a meeting commonly called the Earth Summit,
The United Nations Framework Convention on Climate Change
(UNFCCC) was established. The UNFCCC currently has 192
Parties (Countries) as members. Parties to the UNFCC were
categorised thus:
–– Annex I countries (industrialised countries and economies in
transition);
–– Annex II countries (a sub-group of Annex I – developed
countries which pay for costs of developing countries);
–– Developing countries (not required to reduce emission levels
unless developed countries supply enough funding and
technology).
UNFCCC has met annually at its Conference of the Parties (COP).
At the third conference (COP 3) in Kyoto in December 1997, the
Kyoto Protocol was adopted, which sets out mechanisms for:
–– Emissions trading – known as ‘the carbon market’.
–– Clean development mechanism (CDM) – which establishes
the principle of allowing a country with an emission-reduction
or emission-limitation commitment to implement an emissionreduction project in developing countries. Such projects
can earn saleable certified emission reduction (CER) credits,
each equivalent to one tonne of CO2, which can be counted
towards meeting Kyoto targets.
–– Joint implementation – allowing a country with an emission
reduction or limitation commitment under the Kyoto Protocol
to earn emission reduction units (ERUs) from an emissionreduction or emission removal project in another country with
a reduction/limitation commitment.
16 The Institution of Structural Engineers | Sustainability Briefings
The mechanisms were intended to help stimulate green
investment and help Parties meet their emission targets in a
cost-effective way. As a result of the Kyoto agreed mechanisms
the European Union emissions trading scheme was established in
January 2005.
Many countries ratified the protocol (186 countries – accounting
for around 64% of global emissions) with the notable exception of
the US (accounting for around 36% of global emissions).
Contrary to popular belief, the Kyoto Protocol will not expire in
2012. However, in 2012, Annex I countries must have fulfilled
their obligations of reduction of greenhouse gases emissions
established for the first commitment period (2008-2012). The
Kyoto Protocol is a first step; the UNFCCC requires modification
until the objective is met. The non-binding ‘Washington
Declaration’, (a group of developed countries meeting in February
2007) agreed in principle on the outline of a successor to the
Kyoto Protocol. This would be a global cap-and-trade system
(continually reducing carbon quotas driving a carbon trading
system that would bring an efficient development of a low-carbon
economy) that would apply to both industrialised nations and
developing countries, and it was hoped that this would be in place
by 2009.
The 15th conference (COP 15) has recently concluded in
Copenhagen. The following notes provide some advice on the
outcome and what it might mean for Institution members.
What was agreed at COP 15?
Before the Copenhagen Conference concluded an agreement
was put together and named the Copenhagen Accord. The
following statements are in the Copenhagen Accord:
Temperature: ‘The increase in global temperature should be below
2º’. Many nations including the Alliance of Small Island States
(AOSIS) wanted a lower maximum of 1.5ºC.
To date it has been estimated that the 500000Mt of carbon
released since the start of industrialisation (circa 1750) have
caused just under 1ºC of global warming. Other things have
affected global temperature but their effects more-or-less cancel
out over this period.
Carbon release limits are based on the premise that if the total
should be limited to 1 trillion tonnes and if we release another
500bn tonnes, we commit the Earth to a most likely warming of
about 2ºC.
There was some expectation, at least from Bali (COP 13), that
Copenhagen would deliver a rational legally binding global
framework. Rational, in the sense of looking at how much
‘atmosphere’ there is left and finding a ‘fair’ means of sharing this
out around the world.
The amount of carbon released can be expressed in a parts per
million volume (ppmv). For a 550ppmv target then there is 40%
‘left’ available.
The 2º rise having been pledged, carbon release agreements of
the future will use the rationing of the remaining 500bn tonnes
(550 ppmv) in forming rules in cap and trade agreements.
Peak date for carbon emissions: ‘We should co-operate in
achieving the peaking of global and national emissions as soon as
possible, recognising that the time frame for peaking will be longer
in developing countries …’
Some nations wanted to set a date for emissions to fall, but this
should please developing countries.
Emissions cuts: ‘Parties commit to implement individually or jointly
the quantified economy-wide emissions targets for 2020 as listed
in appendix 1 before 1 February 2010.’
This phrase commits developed nations to start work almost
immediately on reaching their mid-term targets. For the US, this is
a weak 14-17% reduction on 2005 levels (equivalent to 3-5% on
1990 levels); for the EU, a still-to-be-determined goal of 20-30%
on 1990 levels; for Japan, 25% and Russia 15-25% on 1990
levels. The accord makes no mention of 2050 targets, which had
been included in earlier drafts.
Forests: ‘We recognise the crucial role of reducing emission from
deforestation and forest degradation and the need to enhance
removals of greenhouse gas emission by forests and agree on the
need to provide positive incentives to such actions through the
immediate establishment of a mechanism including REDD-plus,
to enable the mobilisation of financial resources from developed
countries’.
It has been estimated that more than 15% of emissions are
attributed to the clearing of forests but there are no safeguards
attached to this commitment. REDD, or reduced emissions
from deforestation and forest degradation is a controversial
mechanism to control loss of forests. The basic concept is simple:
governments, companies or forest owners in the South should be
rewarded for keeping their forests instead of cutting them down.
The idea of making payments to discourage deforestation and
forest degradation was discussed in the negotiations leading to
the Kyoto Protocol, but was rejected. REDD developed from a
proposal in 2005 by a group of countries calling themselves the
Coalition of Rainforest Nations. Two years later, the proposal was
taken up at the Conference of the Parties to the UNFCCC in Bali
(COP 13). Agreement on REDD was planned for at COP 15.
Money: ‘The collective commitment by developed countries is
to provide new and additional resources amounting to $30bn for
2010-12… Developed countries set a goal of mobilising jointly
$100bn/year by 2020 to address needs of developing countries.’
Without this cash there would have been no agreement at
Copenhagen. It provides for rich nations to support developing
countries’ efforts. Longer term, a far larger sum of money will
be committed to a Copenhagen Green Climate Fund but the
agreement leaves open the questions of where the money will
come from, and how it will be used.
What was not agreed?
An attempt to replace Kyoto: Early drafts had included the
preamble ‘Affirming our firm resolve to adopt one or more legal
instruments …’ but it created a negotiation obstacle. The Kyoto
Protocol includes an important distinction between developed and
developing countries. This ‘twin-track’ approach was expected
to be adopted in any agreement coming out of the Copenhagen
conference. Kyoto established the ‘polluter pays’ principle
and developing countries were not prepared to adopt a single
agreement. Europe, Japan, Australia and Canada are desperate
to move to a one-track approach, but developing nations refused
to kill off the protocol.
Deadline for a treaty: ‘… as soon as possible and no later than
COP 16 …’ appeared and disappeared on the last day of the
Conference. It set December 2010 as the date for the conclusion
of a legally binding treaty. The final text dropped this date but it is
likely that we will hear Governments and NGOs say that COP 16
(Mexico) should become the milestone COP 15 (Copenhagen)
was meant to be.
Outcome – how the Copenhagen Accord affects the various
Parties
The United States
The Copenhagen Accord means that the US does not have
the problem of having to address a climate change bill. Their
system of patronage through financial support of politicians
makes it unlikely that they could implement a Climate Change
Act, meaning that the US is unlikely to sign up to any legally
enforceable international agreement.
However it is interesting to note that Sen. John Kerry announced
at Copenhagen that he expected a US Climate Change Bill to
clear both the House and the Senate next year. 33 out of 50
states have emission targets, which shows a considerable level of
commitment to emissions reductions in the US.
China and the developing world
China, with other developing countries were put under pressure
to reduce their greenhouse gas emissions. They did not lose
face – indeed they displayed strength in the face of pressure from
developed countries to ditch the twin-track process established
in Kyoto.
China has adopted a position of reducing carbon intensity by
40%, i.e. reducing the rate of increase.
The third world
The big losers are the poorest nations of the world which are
bound to suffer most from the suggested 2º temperature rise
and there is much agreement on the imminent effects of climate
change.
At the launch of the Intergovernmental Panel on Climate Change
(IPCC) working group report on climate change (Sept 2007)
Professor Parry, co-Chair, said: ‘We are all used to talking
about these impacts coming in the lifetimes of our children and
grandchildren. Now we know that it’s us.’ He said the international
response to the problem had failed to grasp that serious
consequences such as reduced crop yields and coastal flooding
were now inevitable. ‘Mitigation has got all the attention but
we cannot mitigate out of this problem. We now have a choice
between a future with a damaged world or a severely damaged
world.’
At the same event the trade and development minister, Gareth
Thomas said: ‘Failing to tackle it [climate change] will lead to
floods, droughts and natural disasters which can destroy poor
people’s lives as well as their livelihoods.’
Dr Rajendra Pachauri, Chairman, IPCC, not surprisingly, spoke
diplomatically but strongly in his speech for the opening ceremony
for COP 15. He said: ‘Available research suggests a significant
future increase in heavy rainfall events in many regions, including
some in which the mean rainfall is projected to decrease.
The resulting flood risk poses challenges to society, physical
infrastructure and water quality. It is likely that 20% of the world
population, which as a fraction could exceed two billion people,
will live in areas where river flood potential could increase by the
The Institution of Structural Engineers | Sustainability Briefings 17
2080s. In Africa, by 2020, between 75 and 250 million people are
projected to be exposed to water stress due to climate change,
and in some countries on that continent yields from rain-fed
agriculture could be reduced by up to 50%.’
There is neither agreement in place to limit rises to that nor any
legal agreement on mechanisms to achieve the agreed 2º limit.
Low-lying countries will be lost – and soon.
The United Kingdom
The UK came out of the Conference with some political credit.
They were praised for achieving the $100bn/year commitment to
developing countries.
Greenhouse gas emissions are still limited by the Kyoto
mechanism and the EU already has a strong commitment
to reduction of carbon emissions. The UK has the strongest
climate change legislation in the EU. However, other countries
have committed more funds than the UK has in supporting the
stimulation of green technology. Thus the UK is likely to find
itself importing new technology to comply with its own stringent
legislation (the Climate Change Act; the Carbon Reduction
Commitment and implementation of the Code for Sustainable
Homes).
The lack of agreement on reducing carbon quotas has meant
the price of carbon has fallen on the international markets,
leading to a lack of incentive for industry to invest in low-carbon
technology. Development of low carbon industry is a reality for
the UK economy – UK law drives it. As they have to move to low
carbon technology (to meet legal emissions limits) but do not have
the financial benefit of carbon trading to pay for the cost (due
to low value of carbon credits) it is probable that the impact on
construction will be felt more through the high price of energy and
high embodied energy products rather than in direct innovation.
Unless other developed nations move towards targets of similar
stringency, the UK may find itself being put in an uncompetitive
situation, which may lead to internal political pressure to reduce
current UK commitments. Whatever happens it will be driven by
the price of energy and the relative cost of fossil fuel energy and
renewable energy.
COP 15 success or failure?
It seems that the best to be said of COP 15 is that it is two steps
forward and one step back. It has certainly failed the poorest
nations of the world. The non-governmental organisations (NGOs)
of the world were excluded from the UN official conference and
so they lacked influence on the outcome. The issues surrounding
climate change are complex and the conference has not
succeeded in making them any clearer to the non-specialists.
The concept of the trillionth tonne of carbon may be a way of
communicating some of the complexity in an understandable
manner.
Since 2006 the head of the UNFCCC Secretariat has been Yvo
de Boer. In 2008 he said: ‘Copenhagen, for me, is a very clear
deadline that I think we need to meet, and I am afraid that if we
don’t then the process will begin to slip, and like in the trade
negotiations, one deadline after the other will not be met, and we
sort of become the little orchestra on the Titanic’.
In 2009 he said that everything will be sorted out ‘in Mexico one
year from now’.
18 The Institution of Structural Engineers | Sustainability Briefings
The future – beyond COP 15
The effect of climate change is unequal – the UK is in the fortunate
position of being less directly affected than most. The poorest
countries of the world will be worst hit and surely this means
that those who have been most responsible for the emissions
causing climate change have a responsibility to act. Anyone who
is sceptical of the science behind man-made carbon emissions
leading to climate change should make reference to the Royal
Society website and in particular their publication Climate Change
Controversies – A Simple Guide (http://royalsociety.org/policy/
publications/2007/climate-change-controversies/).
Presumably the reason that a ‘rational framework’ was not
agreed at Copenhagen was because both the developed and
the developing countries saw it as too expensive – too restrictive
on their economies. But, as climate change continues, there will
be agreement on how to limit emissions. As a legally binding
limit (which would drive carbon price) does not seem to be
possible, it seems unlikely that the future will be a ‘cap and trade’
mechanism. Perhaps we will see taxes on carbon emissions – a
‘carbon tax’ has been discussed for many years and if a marketdriven system cannot be established, then a tax seems inevitable.
Although the world’s politicians failed to reach agreement, many
companies and other organisations recognise the imperative to
act and are adopting carbon reduction strategies. There was
no global agreement at Copenhagen but the development of
low-carbon solutions as a requirement of a client’s brief will be
the most obvious impact on engineers. We will see low carbon
solutions (energy generation and construction) continuing to
be of importance. They will provide considerable professional
opportunities for engineers to use their skills and knowledge to
meet this challenge positively.
Responsible sourcing
The demand for responsible sourcing is being driven by a number
of factors not least of which are increasing corporate and social
responsibility, protection of brand image and assurance of security
of supply. In addition, there are also sustainable procurement
initiatives and projects supported by Government such as
London 2012 and the ‘Strategy for Sustainable Construction’.
The latter has established a target that 25% of products used
in construction projects should be sourced from schemes
recognised for responsible sourcing by 2012. Assessment tools
such as BREEAM and the Code for Sustainable Homes award
credits for responsibly sourced materials.
Example aspects of responsible sourcing are treatment of workers
and material traceability:
1. The legislative framework within the EU contains a Social
Charter which provides legal protection against ethical and
social exploitation. Such legislation is not common outside
of the EU and organisations need to ensure their supply
chain operates to the minimum standards recommended
by the International Labour Organisation (ILO) in order to
demonstrate responsible sourcing.
2. The specifier/purchaser should be able to identify the source
of the key components and therefore the conditions under
which the material was extracted or harvested. This requires
a raw material inventory management system which is also
known as the ‘chain of custody’. While it is important to
know the origins of the components it is equally important
to know that any ‘added value’ steps in the supply chain are
equally committed to improve their sustainable performance.
Certification to recognised management systems and
performance reporting helps ensure that consistent values are
present along the supply chain.
The current BRE responsible sourcing standard, BES 6001
Framework Standard for the Responsible Sourcing of
Construction Products, published in 2008, provides a common
benchmark for construction products to gain credit under both
BREEAM and the Code for Sustainable Homes schemes.
BES 6001 considers the activities associated with responsible
sourcing (see Figure 1) together with their delivery mechanism
using certified management systems. It therefore provides a
benchmark to compare all construction products on an equal
basis and it is likely to provide a single criterion for responsible
sourcing performance in future updates to the sustainable building
schemes. The standard allows the recognition of four levels of
performance that range from pass to excellent.
Responsible Sourcing
Material
Ethical
Traceability
Legal Compliance
Employment rights
Health and Safety
Extraction / Harvesting
Manufacturing, Processing and
Supply
Supply Chain management
Quality management
Environmental management
Investment in
employees
Working with local
communities
Greenhouse gas emissions
Resource use
Waste management
Water extraction
Transport impacts
Figure 1 The activities of the supply chain covered by the responsible sourcing
standard BES 6001
BS 8902
Provides framework for
sector scheme.
Lists responsible sourcing
issues to be considered as
part of sector scheme.
Accreditation Body
Approves sector scheme
(i.e. satisfies BS 8902)
Establishes processes for
certification bodies.
Sector Scheme Council
Authors and maintains
sector scheme in
acordance with BS 8902.
Certification Bodies
Certifies products
against sector scheme.
Stakeholders
Provide feedback on
sector scheme.
Figure 2 How a sector scheme is set up under BS 8902
The British Standards Institution has subsequently produced
a standard for responsible sourcing of construction products
(BS 8902). The standard provides the basis for the development
of individual sector schemes as shown in Figure 2. The sector
schemes can potentially have the same scope as BES 6001;
however, the threshold performance requirements of BES
6001 are more prescriptive than BS 8902. As a consequence
certification to BS 8902 does not ensure equivalence between
different materials. The BES 6001 framework also supports
sector schemes and could be developed to gain accreditation
under BS 8902. Both standards can be used to help support
responsible sourcing in supply chain management.
The Institution of Structural Engineers | Sustainability Briefings 19
The Structural Engineer 88 (6) 16 March 2010
Customers, clients and stakeholders are increasingly demanding
that responsible sourcing is embedded within the supply chain.
They want to know where materials and products come from,
how the workers in the supply chain are treated and be assured
that the environmental impacts of the materials and associated
components, coatings and by products are being actively
managed and minimised. The structural engineer has a vital
role to play, being tasked with the specification and hence by
implication the responsible sourcing of a significant proportion of
construction materials.
Briefing Note 9
This briefing note explains the vital role of the structural engineer in specifying sustainable
materials and products
CHP: a guide for structural engineers
Briefing Note 10
This briefing note provides a basic guide to the different types of CHP systems, how they are used
and the design challenges they pose
Combined heat and power, or CHP as it is commonly known,
is essentially the combined generation of heat and electrical
power. Put simply, a CHP system is a system that uses fuel in
a thermodynamically efficient manner to produce both usable
heat and electrical energy. The effective use of both the heat
and electricity generated by CHP can increase the efficiency of
energy use upwards of 70% thus enabling less fuel to be used to
produce the same amount of usable energy.
The Structural Engineer 88 (9) 5 May 2010
The CHP system can either be designed or sized to produce a set
thermal output with electricity being considered as a usable byproduct. Such systems are known as ‘thermally led’ or designed
/sized to provide a certain electrical output with heat being
considered as the usable by-product i.e. ‘electrically led’.
CHP systems that are primary producers of heat, and from which
the waste heat is recovered to generate electricity, are known
as ‘bottoming cycle plants’ whereas CHP systems that primarily
produce electricity but then re-use the heat recovered from the
process for other uses are often known as ‘topping cycle plants’.
The primary generating focus of the plant can play a major part
in the location of the plant itself. The transportation of heat as
hot water/liquids over long distances often necessitates costly
and commonly inefficient heavily insulated pipes and pumps.
Hence thermally led or bottoming cycle CHP plants tend to be
located close to the point of use of the heat as a result of the
less costly and more efficient means of transmitting electricity.
However electrically led or topping cycle CHP systems can easily
be placed remotely to the point of use of the electricity due to the
comparatively low cost of the distribution wiring and the relatively
low losses associated with transmitting electricity within a cable
network.
CHP plants are more commonly utilised on large scale industrial
facilities such as steelworks, oil refineries, paper mills and
chemical works.
They can also be adopted to great effect on commercial mixed
use developments where differing thermal/electrical loads and the
energy time demand profile promotes a balancing out of energy
demand thus allowing a broad population of users to benefit
from an improved effective energy generation. A classic example
of such a case would be a mixed use development which
consisted of a snow dome adjacent to a residential development
and school; the energy expelled from the operation of the snow
dome could be used to heat and power the adjacent residential
development and school.
CHP systems are also well suited for use with district heating
systems.
CHP can also be highly beneficial in large industrial facilities
that have large electrical demands and cooling loads such as
semiconductor manufacturing facilities; the excess heat generated
by turbine engines generating electricity can be utilised to
provide heat to meet the high levels of cooling loads by means of
‘absorption’ cooling.
CHP systems can vary in size and type. Common systems in use
at the larger scale include:
–– Gas turbine CHP plants which utilise the waste heat in the flue
gas of the gas turbines;
–– Gas engine CHP plants which use a reciprocating gas engine;
20 The Institution of Structural Engineers | Sustainability Briefings
Figure 1 A CHP engine
awaiting installation on its
foundation block within a
plant room (Courtesy J. H.
Morris)
this is generally considered more competitive than a gas
turbine up to about 5MW.
–– Combined cycle power plants which are adapted for CHP;
–– Steam Turbine plants that use the heating system as the
steam condenser for the steam turbine;
–– Molten carbonate fuel cells which have a hot exhaust and are
very suitable for heating.
Smaller systems may use a reciprocating engine of some form
to generate the electricity with the heat being recycled from
the exhaust and the radiator. These systems can prove more
economic for smaller demands due to the relatively lower cost of
smaller diesel and gas engines.
An interesting example of a CHP system is the Masnedo CHP
power station in Denmark which burns straw as its primary fuel
and from which reclaimed heat is fed into a district heating system
which heats adjacent greenhouses.
CHP micro-generation, which can be used in residential
properties or small to medium size buildings, are considered to be
a very effective means of reducing carbon. Different technologies
such as micro-turbines, internal combustion engines, stirling
engines, closed cycle steam engines and fuel cells are in use in
such systems to generate heat for use in space heating or hot
water systems with the electricity by-product being used within
the property or, if permitted, sold back to the grid.
How does CHP affect me as a structural engineer?
Projects on which CHP is adopted can add the following
challenges to a project:
–– Increased plant room provision, with associated increase in
areas of higher floor loading, to account for in the structural
design of the scheme;
–– Increased demands on clear spans within plant room areas
housing boilers and turbines;
–– Increased provision of fuel storage areas and delivery systems
within plant rooms, particularly when bio-fuels are adopted;
–– The need to integrate turbines/generators into schemes with
the associated provision of potentially complex foundation
blocks and acoustic isolation, needing consideration of
vibration and noise issues, as well as load carrying capability;
–– In the case of district heating systems, the potential provision
of extensive above and below ground pipeways and ducts
to distribute heating pipework, and the associated design of
such sub-structures.
Recycled and secondary aggregates in concrete
Introduction
Recycled and secondary aggregates are generally formed
of crushed construction waste or by-products of industrial
processes, but can also include some post-consumer waste
products such as crushed bottle glass. Construction waste
can be divided into potentially good quality material, essentially
crushed concrete (RCA), and lower quality material which can
include high proportions of crushed masonry (RA). Industry byproducts can similarly be divided into high and lower performing
materials.
Terminology
Terminology relating to recycled and secondary aggregates varies
between users with the term recycled aggregate often being used
to describe all non-primary aggregates although the term recycled
and secondary aggregate (RSA) is preferred in this briefing.
Nevertheless, it is convenient to make various distinctions.
BS 8500-11 provides definitions for two types of recycled
aggregate suitable for use in some concreting applications:
–– Recycled concrete aggregate (RCA) is aggregate principally
comprising crushed concrete.
–– Recycled aggregate (RA) is aggregate resulting from the
reprocessing of inorganic material previously used in
construction.
Strict composition limits for coarse recycled aggregates (RCA
and RA) for use in concrete are provided in Table 2 of BS 8500-2:
20062. Other recycled aggregates include spent rail ballast and
recycled asphalt although the latter may not be suited to use in
concrete.
Secondary aggregates (SA) are generally by-products of industrial
processes which have not been previously used in construction.
They can be divided into manufactured SA (including air-cooled
blastfurnace slag, sintered fly ash (Lytag) and crushed glass), and
natural SA (including china clay stent coarse aggregate, slate
waste, and china clay sand).
Demand and use of aggregates
The demand for aggregates for use in concrete and other
construction applications is enormous (currently estimated at over
250Mt in the UK/pa3). Whilst they are abundant materials, and
the mineral planning process and the work of the Environment
Agency seeks to ensure minimum impact socially and
environmentally, exploitation of aggregate sources near population
centres, even small ones, and in areas of scenic beauty, has
always been unpopular. There are, however, potential sources of
granular materials that go to waste with the consequential issues
of land-fill and, in the cases of china clay waste and slate waste,
aboveground dumping. Use of this RSA can reduce the rate of
depletion of natural resources and reduce problematic waste.
Concrete containing recycled concrete aggregate is now
becoming available in limited quantities from some suppliers.
China clay sand and coarse aggregate (stent) are commercially
available in the UK. Air-cooled blastfurnace slag is also available
but from two of the three UK sources is generally only suitable
for use in low strength concrete. Sintered fly ash lightweight
aggregate is readily available in some markets but is currently
imported. Spent railway ballast has recently become available
from some suppliers.
Recycled aggregates are generally only suitable to replace a
limited proportion of the natural coarse aggregate and little, if
any, of the sand fraction. Research and experience may allow the
currently accepted proportions to increase without compromising
performance. Where the project allows, specific trials, testing and
careful selection of materials may speed this trend (e.g. the use of
crushed railway sleepers in the Wessex Water HQ allowed 40%
replacement of coarse aggregate against the industry norm of
20%). Some secondary aggregates can be used to completely
replace the natural coarse and/or sand fractions although existing
mix designs appropriate for natural aggregates may need to be
modified.
Standards for aggregates
The European Standard for aggregates for concrete4 has been
updated to include recycled aggregates. Although it does not
yet cover ‘unfamiliar materials from secondary sources’ such as
crushed glass, it does include specific requirements for air-cooled
blastfurnace slag. Secondary natural aggregates, such as china
clay stent or slate waste, should meet the requirements of the
standard in the same way as any primary natural aggregate.
Many other countries may not yet have appropriate standards
and, even where standards exist, there may be regulatory or
client specification barriers to overcome. Materials outside the
scope of standards should be used with caution – just because a
material is hard and granular doesn’t mean it is suitable for use in
concrete!
Use of RSA will generally require forward planning to:
–– identify suitable materials, sources and suppliers (location,
quantity, ability to supply);
–– assess suitability, quality and variability (for established or
previously used materials this may already be available);
–– review the feasibility of any on site source and requirements of
meeting legislated waste protocols if transporting materials to
the site;
–– obtain agreement of client, contractor and concrete supplier;
–– explore the economics;
–– allow the producer to perform concrete trials to establish mix
designs and provide assurance of required properties;
The Institution of Structural Engineers | Sustainability Briefings 21
The Structural Engineer 88 (15/16) 3 August 2010
There are already mechanisms including aggregate levy and
landfill tax to provide economic incentives to the construction
industry to use recycled aggregates. The role of the structural
engineer is to ensure the appropriate use of both recycled and
secondary aggregates. A limited percentage replacement is
usually permitted under BS 8500.
The UK produces about 70Mt of RCA each year, and it is used in
a wide variety of building and infrastructure applications. Recycled
aggregates are already in use partly as a result of the landfill tax
and aggregate levy influencing the supply industry to increase
its use, but also due to client demand for so-called ‘sustainable
construction’. The overall use of RSA in the UK is well above the
European average3.
Briefing Note 11
In considering the use of recycled and secondary aggregates, the structural engineer should
consider the issues set out in this briefing
–– prepare the specification (‘Recycled aggregates shall be used’
is not sufficient).
These requirements can be significant and currently a potential
barrier to use. As familiarity with the material and supply
options increases, this issue should become less of a problem.
In all projects the benefits of meeting technical performance
requirements effectively and economically will probably be central.
There is also a need for careful planning if material is to be
retained and reused on site, and on constrained sites it may not
be practicable.
Principles
Requirement of recycled and secondary aggregates should be
considered for any project following the principles set out below.
–– RA can be a highly variable and is generally suitable only for
use in low grade concrete; it is not recommended for use in
structural concrete.
–– RCA should only be used if it is locally available (within roughly
30 miles) or would otherwise go to landfill. Long distance road
transport of RCA is to be discouraged.
–– The deployment of RCA to replace primary aggregates in
situations where both fine and coarse portions can be used
(e.g. as fill) should be given preference to deployment in
structural concrete.
–– Secondary aggregates can be transported a significant
distance by rail or water if they would otherwise be treated as
a waste. In the UK there are secondary aggregates available
to some locations, but not all, which would otherwise be
stockpiled or treated as waste.
The primary aggregate replacement level should be chosen
to ensure that the Portland Cement content is not significantly
raised.
Project examples
The prestigious office development at One Coleman Street in the
City of London is recognised as the first major use of china clay
stent coarse aggregate in concrete outside the South West of the
UK5. The stent was used to completely replace the normal primary
coarse aggregate in pile-caps, floor slabs and the structural
frame. China clay sand was not used because of its increased
cement demand.
China clay stent is also being used, alongside a small proportion
of ground glass sand, to meet the stringent recycled/secondary
content requirement for concrete in the 2012 London Olympics
construction. The proportion of stent aggregate in this case varies
with the strength class of the concrete.
Air-cooled blastfurnace slag from Port Talbot is routinely being
supplied into structural quality concrete by at least three readymixed concrete plants in the Cardiff and Swansea area and
has recently become available in the London area. At least one
concrete supplier is meeting customer demand for RSA content
through the use of spent railway ballast.
Drawbacks
Natural aggregates are still cheap and plentiful in most areas with
a well developed commercial supply infrastructure. There are
few commercial sources of recycled or secondary aggregates
although that situation is slowly changing as demand grows.
22 The Institution of Structural Engineers | Sustainability Briefings
Sources of secondary materials are, in some cases, far from
centres of construction activity (e.g. china clay waste in Cornwall
and slate waste in Wales). Use of RSA may carry a cost penalty
until their use becomes more widespread or greater incentives
are provided by governments or the waste producers. Some RSA
may carry a need for increased rates of testing and, possibly,
increased cement content which can potentially offset any
sustainable advantage of the RSA.
The British Standard for Concrete2 excludes the use of coarse
RCA in concrete for exposure conditions that include chlorides,
significant freeze-thaw or aggressive ground conditions unless
suitability in such uses has been demonstrated. No guidance at all
is provided on the use of RA or fine RCA.
Potentially longer supply distances can increase the transport
impacts of moving materials. Although aggregates contribute a
small proportion of overall concrete eCO2, RSA can increase mix
eCO2 through increased transport distances and if the cement
demands are increased to ensure performance.
Academic research tends to be optimistic about the properties
of concrete made with secondary aggregates from some unlikely
sources (e.g. sewage sludge ash and periwinkle shells). It is
therefore essential to be sure materials are appropriate for general
application within the established supply chains.
In summary, RSA should be considered by following the
principles set out above in order to ensure that the best practical
environmental option is achieved.
References
1. BS 8500-1: Concrete – Complementary British Standard to
BS EN 206-1 – Part 1: Method of specifying and guidance for
the specifier, BSI, 2006
2. BS 8500-2: Concrete – Complementary British Standard to
BS EN 206-1 – Part 2: Specification for constituent materials
and concrete, BSI, 2006
3. Sustainable Development Report
Quarry Products Association, 2007
4. EN 12620:2002 + A1:2008: Aggregates for concrete,
European Committee for Standardisation, CEN, 2008
5. Marsh, B. K.: ‘One Coleman Street – a case study in the use
of secondary materials in concrete’, The Structural Engineer,
85/9, 1 May 2007, p 35-37
Comment from reader
I recall that as a member of the Hawkins committee dealing with
minimisation of alkali-silica reaction we included the following in
the 3rd edition of the Concrete Society report.
“The classification of recycled aggregates (including crushed
concrete and other demolition waste) as high reactivity is a
precautionary measure pending further knowledge about their
long-term behaviour. Reclaimed aggregates, which are natural
aggregates from fresh concrete, should be treated on the basis of
the reactivity class of the original aggregate.”
This was in 1999. I would be grateful if this could be brought
to the attention of those dealing with the briefing. It would be
interesting to know if the situation has changed since the issue of
Concrete Society report.
Response from Panel
The current and most up to date guidance is in BRE Digest 330,
2004 Edition. In particular see page 5 of BRE Digest 330 Part 2.
Recycled concrete aggregate (RCA) is defined as crushed
concrete with not more than 5% masonry, and if the original
concrete did not contain a highly or extremely reactive aggregate
then the RCA is not classed as highly or extremely reactive. A
nominal contribution to the alkali content of the concrete from the
RCA should be included.
All other recycled aggregate should be assessed on a case by
case basis as the potential composition can be so wide, and the
recommendation is that it should be classified as high reactivity.
The position with respect to reclaimed aggregates appears to
be the same, they should be classified in terms of reactivity of
the original aggregate type or combination. The mixing of low
reactivity aggregate with high reactivity aggregate means that it
would all be classified as high reactivity.
The Institution of Structural Engineers | Sustainability Briefings 23
Carbon trading
Briefing Note 12
Reduction in carbon emissions is central to the negotiations at
the UN COP meetings. Following Copenhagen (COP 15) (see
sustainability briefing in The Structural Engineer 88/2, 19 January
2010), the negotiations will resume later in 2010 at Cancün in
Mexico. This note, on carbon trading, has been prepared to
help structural engineers in understanding this complex topic,
to encourage them in following reports and to enable them in
contributing to discussions.
The Structural Engineer 88 (18) 21 September 2010
In a world where there is an obligation to reduce carbon
emissions, Governments could issue an instruction to all carbon
emitters that they must reduce emissions by a certain amount.
This system of command and control makes no distinction,
between carbon emitting companies, of the cost of cutting
carbon.
What is emissions trading?
Emissions trading is a mechanism devised to regulate and control
carbon emissions. There are two types of market-driven schemes
which create forces to incentivise reduced carbon emissions.
‘Price instrument’ using a tax, levied at a fixed price, with the
quantity of emissions allowed to float. A carbon tax increases
the competitiveness of non-carbon technologies compared to
the traditional burning of fossil fuels, thus helping to protect the
environment while raising revenues.
‘Quantity instrument’ using a fixed quantity allowance and floating
price. In this system a value is created for carbon emissions,
which are then either exchanged or traded. Government
progressively reduces the size of the fixed quantity allowance,
maintaining and increasing the value of carbon credits. This is
‘emissions trading’.
Emissions trading should ensure that emissions reductions are
made at least cost to industry. Such a system is attractive to
Governments, which need to maintain competitiveness of their
countries. This is in contrast to a command and central control
mechanism, where emissions might be reduced by mandate,
regardless of cost to the company. It is also more attractive than
a taxation system, which requires detailed Government invention
and operation; in contrast a trading scheme, once operating,
requires minimal Government intervention.
The effect of incentivising efficient carbon reduction, through least
cost to industry, is demonstrated by the example in Table 2.
In this example, Company A and Company B are both required
by law, through an emissions allocation, to either reduce
emissions by 20% or to trade emissions to an equivalent emission
reduction. Under the command and control system (Table 1), both
companies cut emissions – this costs company A more than it
costs Company B and the combined cost is €3400. Under an
emissions trading system, companies are allowed to buy from the
Start
Cost of
End
Carbon Cost of
emissions reduction emissions cost/
reduction
credit
Company 100t
€100/t
80t
–
A
€2000
Company 100t
€70/t
80t
–
B
Total
20 x 100 =
20 x 70 =
€1400
200t
160t
€3400
Table 1 Command and control – Government issues an instruction, enforced by
fines, that all emitters of carbon should produce a 20% cut in emissions
24 The Institution of Structural Engineers | Sustainability Briefings
market if their own emissions cut is insufficient or to sell surplus
emissions to the market if their cut exceeds their allocation.
The ability to trade carbon between the companies provides an
incentive to the company that can cut carbon more cheaply (in
this case Company B). Both companies are required to show
a saving of 20t of carbon. The cut is enforced by fines which,
to be effective, must cost the company more than reduction in
emissions. Company A reduces its emissions by 10t and buys the
other 10t on the market, at €80/t. Company B cuts its emissions
by 30t and sells its surplus of 10t of carbon into the market and
receives €800. Thus, through emissions trading, the saving in
carbon is achieved at an overall lower cost (€3100) than a blanket
cut of 20t per company.
For the market to be effective in driving lower carbon emissions,
there needs to be a shortage of carbon. Shortage drives the price
of carbon credits up, incentivising reduction. Such Government
measures introduced to reduce carbon and to drive up the cost
of carbon credits are called ‘cap and trade’. The cap is an agreed
enforceable limit on emission and trade is the activity of the
carbon market. To make sure this shortage exists, the allowances
under the trading scheme must be less than a ‘business as usual
scenario’.
History
The Kyoto Protocol, which was set to operate in the period 20082012, was introduced to achieve ‘stabilisation of greenhouse gas
concentrations in the atmosphere at a level that would prevent
dangerous anthropogenic interference with the climate system’.
It quantified greenhouse gas emissions targets for ‘Annex 1’
parties (developed countries and countries in transition) and this
led to the EUETS (European Union Emissions Trading System),
the largest multi-national trading scheme in the world and a major
pillar of EU climate policy
The EUETS
The EUETS currently covers more than 12000 installations in
the energy and industrialised sectors, which together account
for more than half of the EU’s emissions of CO2 and 45% of its
greenhouse gas emissions. This is the largest trading scheme in
the world and so it is discussed in some detail.
The EUETS creates a market for carbon emissions, which allows
trading to take place. The trading unit is one unit of carbon dioxide
emitted or 1t CO2e – this is called an EU allowance (EUA). Thus
‘price of carbon’ is the cost of an EUA on the market. Incidentally,
the molecular weight of carbon is 12, that of oxygen is 16 and so
1t of carbon dioxide (molecular weight 44) contains around 1/4t of
carbon.
Start
Cost of
End
Carbon Cost of
emissions reduction emissions cost/
reduction
credit
Company 100t
€100/t
85t
A
+5 x
15 x 100
60
+ 300 =
€1800
Company 100t
€70/t
75t
B
Total
200t
–5 x
25 x 70
60
– 300 =
€1450
160t
1600 + 1500
= €3100
Table 2 Emission trading – Assuming carbon price of €80/t
Start
Cost of
End
Carbon Cost of
emissions reduction emissions cost/
reduction
Start
Cost of
End
Carbon Cost of
emissions reduction emissions cost/
reduction
credit
credit
Company 100t
€100/t
85t
A
15 x 100 +
300 =
€1800
Company 100t
€70/t
75t
B
Total
+5 x
60
-5 x 60 25 x 70 300 =
€1450
200t
160t
1600 +
1500 =
€3100
Company 100t
€100/t
100t
A
Company 100t
€70/t
100t
B
Total
200t
+20 x
1200 =
60
€1200
+20 x
1200 =
60
€1200
200t
= €2400
Table 3 Emission trading fails to operate – Assuming carbon price of €60/t – no
incentive for Company B
Table 4 Emission Trading fails to reduce carbon emissions – assuming carbon
price of €60/t and excess of credits in the system
The key to success of the European trading system is setting the
cap on emissions. The cap is set in the National Allocation Plan
(NAP), which is submitted by each Member State and approved
(or not) by the European Commission. Clearly in the market the
cap determines the price of carbon, which determines investment
in the technology, which leads to an efficient reduction in carbon
emissions. Setting the cap too high leads to a price of carbon too
low to justify investment to motivate emission reductions.
Applies to specified industry sectors only. At present these include
power, some building materials, oil and gas, iron and steel, pulp
and paper and ‘other combustion’ but not transport.
Features of the EUETS
–– Allowances operated through NAPs and distributed through
–– Phase I – 2005-2007 – learning period;
–– Phase II – 2008-2012 – Kyoto period;
–– Phase III – 2013-2020.
–– Applies to CO2 only;
A guide to terminology and acronyms in carbon trading
Cap and trade
The principle behind carbon trading. Limit (cap) the amount of emissions legally permitted and allow countries/
operators to buy (trade) certified emissions generated by others. The value of the certified emissions is important. If
certified emissions (carbon credits) are worth too little, there is little incentive for their creation.
Contraction and
convergence
The industrially developed world generates too many emissions. The industrially under-developed world would like
to generate more. Total emissions should reduce thus the developed world’s emissions should contract and the
combined emissions of the developed and under-developed nations should converge on a total that is less than the
present.
EUETS
European Union Emissions
Trading Scheme
Largest multi-national emissions trading scheme in the world.
NAP
National Allocation Plan
National emissions cap for EU member state under the EUETS. For the scheme
work in cutting emissions, the allocation must be less than what would have been
emitted in ‘business as usual’.
EUA
EU emissions Allowance
A carbon credit (allowance) under the EUETS to emit 1t of CO2 equivalent.
Jl
Joint Implementation
Defined in Kyoto Protocol. This produces the ERU.
ERU
Emissions Reduction Unit
Under the Jl, one ERU is the successful emissions reduction equivalent to 1t of
carbon dioxide equivalent.
CDM
Clean Development Mechanism
Defined in Kyoto Protocol. This sets down the Kyoto mechanism for certifying
emissions reductions. CERs are issued under the CDM.
CER
Certified Emissions Reductions
Under the CDM, one CER is the certified emissions reduction equivalent to one
tonne of carbon dioxide equivalent. CERs can be bought from the primary market
(from the party making the reduction) or from the secondary market (resold in
marketplace). These are a form of ‘climate credit’ or ‘carbon credit’ and are used
by countries or by operators to show compliance with obligations under the
EUETS.
CDM/Jl
VER
The mechanisms that define trading under the Kyoto Protocol.
Voluntary Emissions Reductions
Carbon credits developed by carbon offset providers, which are not certified.
The Institution of Structural Engineers | Sustainability Briefings 25
free allocation and auctions;
–– Auction volumes limited to 5% in Phase I and 10% in Phase II;
–– Not all governments auction in Phase II;
–– 100% auction for power section in Phase III.
The EUETS currently covers 2bn t of CO2 per annum. Power
generation accounts for around 30% of EU CO2 emissions and
65% of emissions covered by the scheme.
EUETS and the rest of the world
EUETS is not a closed loop scheme. Installations can set off
emissions by purchasing credits from other countries. The limits to
the amount of trading is set by the Kyoto mechanisms, which are
defined in the Clean Development Mechanism (CDM) and Joint
Implementation (Jl).
Under EUETS, a carbon credit is an ‘allowance’ to emit one tonne
of CO2, hence there is an EU Allowance (EAU). Under CDM/Jl, a
carbon credit is a guarantee that emissions have been reduced
below a ‘business-as-usual’ level. This leads to Certified Emission
Reductions (CERs), Emissions Reduction Units (ERUs) and
Voluntary Emission Reductions (VERs).
Savings in carbon on a CDM registered project in a developing
country can be transferred to an EU emitter, in exchange for
money paid into the developing country.
Summary
Positives:
–– Supports ‘polluter pays’ principle;
The example in Table 2 used a carbon credit price of €80/t. If the
value of carbon credits falls to less than the cost to Company B
of reducing emissions, Company B has no incentive to sell credits
onto the market. Table 3 shows that it costs Company B more to
cut emissions than it receives in trading its surplus on the market.
It would be cheaper for both companies to buy credits on the
market.
The emissions trading market was created by allocations of
carbon credits. Due to the reduced demand for energy caused
by the recession, the market can operate with an imbalance in
carbon credits – credits bought do not have to equal credits
created by emissions cuts. Table 4 shows how the trading
scheme can create a situation where credits are bought in
preference to emissions reductions.
If the emissions trading scheme is to be effective, Government
must intervene to tighten the cap and reduce the availability of
carbon credits. Alternatively they could wait for an increase in
energy demand to drive up the price of emissions. Some say
that the emissions trading scheme is discredited as an effective
mechanism and carbon taxation should be introduced.
Whatever emissions controls are introduced, the structural
engineer will feel the impact of carbon indirectly. If carbon
emissions trading is successful, high carbon emitting operators
will be penalised by having to purchase expensive credits. This will
lead to a continuous reduction in carbon emissions and, in due
course, ‘a low carbon economy’. In a low carbon environment,
high emission products (generally high-embodied carbon
products) will be expensive and the structural engineer will be
deterred from their use through the normal process of economic
forces.
–– Takes in a large number of operators;
–– Secondary market in carbon developing;
–– Phase II price helps continuity of CDM investment;
–– EU companies have gained advantage over competitors in
other countries and have developed links with developing
countries through CDM.
Negatives:
–– Phase I allocations too high and there was a price crash in
carbon in 2006 and 2007 (from €30/t in 2004 to €0.03 in
December 2007);
–– The free allocation led to excess profits and competitive
distortions;
–– Current price collapse, due to recession (€30.53 on 1 July
2008 to €8 in March 2009 to settle to around €15 during the
first half of 2010) could delay investment in clean technology;
–– Carbon trading only relates to supply – it does nothing
directly to incentivise energy reduction by the user. If it leads
to increase in energy prices, this clearly encourages energy
conservation but this is an indirect effect;
–– If the carbon price is too low the incentive towards carbon
reduction is lost – it is cheaper to buy carbon credits than to
cut carbon emissions.
26 The Institution of Structural Engineers | Sustainability Briefings
Post publication comment
Readers are advised that the term ‘Contraction and convergence’
explained in the table A guide to terminology and acronyms in
carbon trading is protected to GCI by IPR and ETS. The term
relates to a specific model of future emissions that was introduced
to the United Nations Framework Convention on Climate
Change (UNFCCC) in 1996 by GCI for the purposes of achieving
UNFCCC-compliance. A full explanation and Definition Statement
for Contraction and Convergence is available at:
http://www.gci.org.uk/briefings.html. Extensive information about
the international acknowledgement of the origin of Contraction
and Convergence and the support for it can be found at
http://www.gci.org.uk.
The reuse of structural components and materials
Figure 2 Dwelling
constructed in
the former Abbey
of St Edmunds,
Suffolk
It may be prudent to clarify what is meant by the reuse of
structural materials as opposed to recycling them. Figure 1 gives
an annotated version of the material use hierarchy agreed by the
EU in directive 2008/98/EC2.
Examples, with estimated UK reclamation volumes where known3
include:
–– Hot rolled and cold formed steel sections – 20000t/y
–– Structural timber, timber sheet products and studwork –
50000t/y
–– masonry (brick and stone) – 1400000t/y
–– precast concrete units
–– sheet piling
–– entire portal frame buildings
–– foundations
There are also many opportunities to reuse structure in situ – not
a modern idea – as indicated in Figure 2, a ‘modern’ dwelling
constructed in a former arch of the 12th century abbey of St
Edmunds.
Currently the reclaimed structural components market is small
and poorly integrated into supplier networks. However, with
perseverance, it is possible to specify and procure these items.
The Beddington Zero Energy Development (BedZED) design team
procured and reused a number of materials including structural
steel beams and columns4 (see Figure 3). In addition, a project
was undertaken in Berlin where precast concrete elements from
a former apartment block were reclaimed and reused in the
construction of a new house5 (Figure 4).
It is also possible to avoid the need to go to a market and instead
identify components that may be directly used onsite. If a new
building is to be constructed on the site of an existing structure,
or perhaps within close proximity, an alternative approach may
Prevention
Avoidance of
excessive materials
via efficient design
pholosophy e.g. via
structural repitition
Reuse
Recovery and direct
reuse of a component
in an application of
equal quality or value
to the source e.g. a
brick reused as a brick
be to consider how the old structural components could be
integrated or reused in the new structure. In other words, instead
of designing a structure and procuring the materials, consider
identifying reusable components first and then developing a
design to make use of them. This is particularly relevant in urban
centres where there is a constant level of renewal of the building
stock. This principle is exemplified in the Reuse of Foundations for
Urban Sites (RuFUS) project, which has produced a best practice
handbook to aid designers6.
By reusing components and materials the structural engineer
can directly achieve a reduction in the embodied energy of the
structure, and possibly the financial cost, as well as additional
advantages associated with a reduced demand on finite
resources.
Challenges facing an increase in the reuse of structural
components include the lack of a mature secondary market,
health and safety issues surrounding the dismantling of buildings,
as well as problems with the processing and assurance of the
components before reuse. In addition, UK and EU legislation has
tended to place more emphasis on the recycling of materials
rather than component reuse which has further hampered
the development of this market. Guidance in designing for
deconstruction as well as research and guidance on the
properties of reclaimed materials will greatly assist in addressing
these challenges. A forthcoming sustainability briefing will set out
Recycle
Recovery and
remanufacture of a
material into a
component of equal
quality to the source
e.g. structural steel
melted and reformed
into structural steel
Other Recovery /
Energy Recovery
Other forms of
recovery may be
possible e.g. burning,
composting
Safe Disposal
Disposal of
non-recoverable
materials with a
minimum negative
impact on human
health or the
environment
Figure 1 Material use hierarchy (with annotations)
The Institution of Structural Engineers | Sustainability Briefings 27
The Structural Engineer 89 (1) 4 January 2011
For the structural engineer, arguably, the greatest scope to
influence the sustainability of a scheme is found in the choice and
specification of the structural components and materials. Which
materials then, can a structural engineer specify as reused?
Briefing Note 13
The construction industry disposes of 120Mt1 of construction
‘waste’ per year, though it is often possible to recover these
materials for reuse and recycling. Much progress has been made
in the recycling of construction materials and this will be dealt with
in separate sustainability briefings. This briefing however, is aimed
at providing an overview of the reuse of structural materials and
what it means to structural engineers.
Figure 3 BedZED steelwork
Figure 4 Precast panels of the Berlin house
the principles of designing for deconstruction.
Bibliography
Despite the challenges to reuse, it is possible to procure and use
reclaimed structural components in new projects, and there are
clear environmental, and possibly financial, benefits in doing so.
It is hoped that engineers reading this briefing sheet may wish
to consider if there are reuse opportunities within their projects
and an increased demand can be created in this sector. WRAP
have prepared a ‘Reclaimed Building Products Guide’4 which
offers further information as to the procurement of reused building
components.
http://www.wrap.org.uk/construction/index.html
References
1. WRAP, 2009. Time for a New Age: Halving waste to landfill,
Waste Resources Action Plan, London, UK
2. Directive 2008/098 European Parliament 32008L0098
http://www.bioregional.com
http://www.salvo.co.uk/
–– Addis, B. and Schouten, J. 2004. Principles of Design for
Deconstruction to Facilitate Reuse and Recycling, CIRIA.
London, UK
–– Addis, B. 2006. Building with Reclaimed Components and
Materials. Earthscan. London, UK
–– BERR, 2008. Sustainable Construction Strategy. Department
for Business, Enterprise and Regulatory Reform. London, UK
3. BigREc Survey, 2007. A survey of the UK reclamation and
salvage trade, Construction Resources & Waste Platform
–– Hobbs, G. and Hurley, J. 2001. Deconstruction and the reuse
of construction materials, Building Research Establishment,
Watford, UK
4. WRAP. 2008. Reclaimed building products guide, Waste
Resources Action Plan. London, UK
–– Howard, N. 2000. Sustainable Construction – the Data,
Building Research Establishment, Watford, UK
5. Charlson, A. 2008. ‘Recycling and reuse of waste in the
construction industry,’ The Structural Engineer, 86/4, 19
February, 2008, London, UK
6. Butcher, A. P. et al. 2006. Reuse of Foundations for Urban
Sites – A Best Practice Handbook, IHS BRE Press, Berkshire,
UK
28 The Institution of Structural Engineers | Sustainability Briefings
Wales and its steps towards zero carbon buildings
The Welsh Assembly Government (WAG) as an executive body of
the National Assembly for Wales takes responsibility for the dayto–day issues of the populace of Wales which includes, of course,
the economy and the environment. The role of WAG includes
making, developing and implementing policy, making sub-ordinate
regulations and proposing Welsh laws.
In May 2009 the WAG set sustainable development as a
cornerstone principle for its work by publishing its document One
Wales; One Planet1 which outlines its Sustainable Development
Scheme and it has supported this strategy by firm commitments
to sustainability that are more advanced than other UK and
European governments.
The contribution that construction can make in achieving its goals
has been acknowledged by the Assembly Government and has
resulted in it setting challenging standards to reduce carbon
emissions and for the diversion of waste from landfill. These efforts
include commitments to set standards for the environmental
performance and resource efficiency standards for new buildings.
The Welsh Assembly Government’s aspiration is for all the
construction projects it directly procures, provides financial
support to, or is in collaboration with to be ‘zero carbon’ by
2011. The same can also be said for projects that are built on
land owned or leased by the WAG. However it appreciates that
a supportive and collaborative ‘step by step’ approach must be
undertaken in order to achieve its goals. WAG is also committed
to reduce greenhouse gases in Wales by 3% a year from 2011 in
areas of its devolved competence.
Working in partnership with the Design Commission for Wales (the
Welsh equivalent of the Commission for Architecture and the Built
Environment) and the Sustainable Development Commission for
Wales, WAG has assembled a working group, the Hub, consisting
of key members of the building industry and housing and
voluntary sectors to lead Wales as a nation in reaching its carbon
emissions reduction target.
‘The Hub’ provides leadership to:
–– deliver a cut in emissions from all buildings;
–– promote commercial opportunities from low carbon building;
–– investigate the skills and training needed in the construction
industry to achieve the goals.
A Green Building Charter2 has been drafted and currently 53
organisations from across Wales have signed up to the Charter.
At present the Assembly Government requires the environmental
impact of developments where it has an influence to be
considered and reduced as much as possible.
The WAG has currently set foundation standards from which it will
continue to develop more stringent and well publicised guidelines.
Currently all new buildings promoted or supported by the Welsh
Assembly Government in the manner described previously are to
comply with the following:
–– Non-residential developments to achieve British Research
Establishment Environmental Assessment Method (BREEAM)
or equivalent ‘Excellent’; and
–– A minimum of 10% (by value) of recycled materials to be used
in all new buildings.
–– The CEEQUAL4 scheme which is the assessment and awards
scheme for improving sustainability in civil engineering and
public realm projects is committed to for site development
and infrastructure projects.
–– The Waste and Resources Action Programme5 (WRAP) is
funded in Wales by the Assembly Government. The WRAP
tools are currently being used on Assembly Government
projects.
The definition of ‘zero carbon’ for new non-domestic buildings is
being developed and WAG has confirmed that Wales will adopt
the definition put forward in England following completion of the
consultation over the document issued by the CLG.
WAG is currently using the attainment of the UK’s Code of
Sustainable Homes3 Level 5 as the indicator of the achievement of
‘zero carbon’ on domestic projects.
WAG is consolidating its efforts to realise its ‘zero carbon’
aspirations by 2011 by encouraging the minimisation of energy
demand, the optimum use of on and near-site renewables whilst
recognising that there needs to be a level playing-field for small
and large developers.
WAG and its partners through the Hub are continuing to support
the industry by developing web-based guidance in the form
of standard details suitable for use on housing, grade A office,
industrial, retail and education projects.
A number of pilot projects are currently being undertaken to
demonstrate how the requirements can be achieved and to obtain
information on buildability, costs and issues which can be shared
across the industry.
In order to share information across the construction industry a
web portal will be created which will be hosted by Constructing
Excellence Wales providing a single point of reference for clients,
designers, builders, suppliers and manufacturers. This will provide
the direction and guidance required to respond to queries.
Legislation has been passed which will transfer building
regulations powers to Wales on 31 December 2011 and WAG
has committed to implement changes to the building regulations
to move towards zero carbon, the first step of which will be a 55%
improvement over the 2006 building regulations. The Assembly
Government also aims to bring forward detailed proposals for
consultation during 2012 with a view to implementation in 2013.
How does this affect me as a structural engineer?
Those structural engineers working in Wales on public sector
projects need to be aware of these initiatives and embrace them
and be involved in the process led by the Hub and WAG.
The Institution of Structural Engineers | Sustainability Briefings 29
The Structural Engineer 89 (3) 1 February 2011
WAG has set very clear goals to enhance the economic, social
and environmental well-being of people and communities within
Wales and in doing so it recognises the important contribution
that sustainable development makes to achieving their goal.
–– Residential developments to achieve as a minimum the Code
for Sustainable Homes3 Level 3;
Briefing Note 14
Wales is a world leader in sustainable development and reducing carbon emissions. Other regions
and nations can learn from the various initiatives outlined in this briefing
Although the attainment of the standards set by WAG’s policies
can be achieved with little or no change in the approach to
structural design that we have been used to over the last decade
there is no reason why we shouldn’t as a profession embrace the
philosophy behind the WAG’s initiatives and make more effort to
design more sustainable structural solutions.
References
1. One Wales: One Planet, a new Sustainable Development
Scheme for Wales, available at: http://wales.gov.
uk/topics/sustainabledevelopment/publications/
onewalesoneplanet/?lang=en
2. Green Building Charter, available at: http://wales.gov.uk/docs/
carbonfootprint/policy/090206greencharter.pdf
3. Communities and Local Government, Code for Sustainable
Homes: A stepchange in sustainable home building practice,
2006, available at: http://www.planningportal.gov.uk/uploads/
code_for_sust_homes.pdf
4. The assessment and awards scheme for improving
sustainability in civil engineering and the public realm, available
at: http://www.ceequal.com/
5. Waste & Resources Action Programme, available at:
http://www.wrap.org.uk/
30 The Institution of Structural Engineers | Sustainability Briefings
Design for deconstruction
Design for deconstruction (DfD) means considering end of use
scenarios during initial design. Design which incorporates re-use
of deconstructed elements is a closely allied but different subject,
and is not covered in this briefing. DfD means ensuring that the
element has some intrinsic value, once deconstructed. End of
life outcomes should be considered in a hierarchy of decreasing
desirability, namely:
–– re-use in situ
–– re-use in a different setting
sold on easily. Otherwise recycling, or other disposal options, will
be the most cost effective.
This shows that it is not sufficient to limit design effort to the
de-mountability of elements. There are simple steps that can be
taken now to improve the potential end of life outcomes.
Information, design for
buildability, loose fit, use
of simple principles
Immediate, medium and
long term value to client
–– energy recovery
–– disposal
This briefing will concentrate on design to facilitate re-use. To be
successful the designer needs to consider the full lifecycle of the
element, as well as end of life. A common misconception is that
DfD is the process of designing de-mountable components. This
is only a small part of the process.
Formal assessment, e.g. Extra service, higher cost
detailed deconstruction
less tangible long term
plan
value to client
Figure 1 Two approaches to design for deconstruction
DfD checklist
What are the positive benefits of design for deconstruction?
–– Plan buildability and deconstruction
The application of DfD principles of considering buildability,
appropriate life, loose fit, easy maintenance, and improved
information will generally prove a low cost, high value part of the
design.
–– Separability - recognise life span and replacement hierarchy
(loose fit)
DfD will reduce waste, reduce the down-grading of materials
and thus avoid resource depletion. Depending on the energy
needed to extract and rework the element into a new setting,
it may reduce energy use. However this is not always the case
as deconstruction, transportation and reprocessing may take
significant energy.
These benefits are increasingly being recognised by the UK
Government. Planning constraints, taxation and building
regulations are used to create market value. Supplier take-back
regulations are already in place in some industries. So, within the
life cycle of most buildings, the value of a building designed with
deconstruction in mind will certainly rise.
How can structural engineers design for deconstruction?
Figure 1 shows the two approaches that are available. A thorough
review and application of DfD will take time and represents an
additional design service. However there are some low/no cost
actions that can be taken by all.
Design for re-cyclability is an easier target to assess and
demonstrate and will lead to different solutions. Current demolition
techniques can, and do, generate high yields of re-cyclate. A clear
hierarchy of outcomes for different elements of the building should
be identified early in the design process.
The key issue in design for deconstruction is ensuring that an
element has value when no longer required in its planned setting.
To understand this it is important to understand the modern
demolition industry and consider how it will operate in future. The
modern demolition industry is highly sophisticated and skilled at
extracting value, in the shortest possible time from an existing
building. Health and safety considerations are a key driving force
and the move away from slow and dangerous hand techniques is
continuous. Demolition is planned and the potential value which
can be realised will be assessed in advance. Investment in time,
plant and storage space will only be made if an element can be
–– Specify appropriate quality
–– Elements will be desirable/re-usable, available in sufficient
quantity and with minimum re-processing
–– Elements will be maintainable
–– Information trail passed with the building (e.g. in O&M folder
and the H&S file)
–– Standardisation
–– Fixings (minimum number removable, aim for mechanical not
chemical)
–– Simplicity – clear load paths, simple connections
For structural engineers the following may prove more successful
than trying to plan for full and complete deconstruction of a
conventional building structure:
–– Provide information about materials and construction
sequence to allow future designers flexibility to provide new
design solutions
–– Use modular construction with mechanical connections
–– Plan for re-use of compound elements, rather than single
ones, to allow selective demolition techniques such as
pancaking
–– Plan for a combination of re-cycling and re-use
How can structural engineers demonstrate and assess DfD?
The formal assessment of the future deconstruction stage of
a current new design is challenging and few precedents exist.
Tools, such as a demolition audit, the ICE demolition protocol,
or reference to existing building material exchange web sites
could be used to form an assessment. There will be energy and
cost involved in reprocessing elements and designing into a new
setting, or re-cycling. This can be assessed based on current
market figures and compared to the energy and impacts of the
use of virgin materials. The comparison may not be favourable.
The Institution of Structural Engineers | Sustainability Briefings 31
The Structural Engineer 89 (4) 15 February 2011
–– recycling
Briefing Note 15
What is design for deconstruction?
This is borne out by the lack of a market for some re-used
building elements. However the estimate will be conservative.
The costs and programme implications of future dis-assembly
rather than demolition may be very high indeed. Reference to
studies of re-used building components is recommended in order
to assess an appropriate module size. These are detailed in a
companion Institution briefing note titled ‘Re-use of structural
components and materials’ (see The Structural Engineer, 89/1
2011).
Summary
Structural engineers can identify low cost actions which will
greatly increase the value of the building components at the end
of their useful life in the building. Structural engineers can, and
should, present these to the client and design team as part of
sustainable design. These can form part of standard practice. For
example structural engineers’ standard specifications can place
a requirement for identification and improved information about
elements.
To provide full consideration of DfD involves additional design
services and research.
Bibliography
–– CIRIA guide C607 Designing for Deconstruction: Principles of
design to facilitate reuse and recycling, 2004
–– TG39 Deconstruction: Deconstruction and Materials Reuse
An International Overview, CIB Publication No. 300, 2005
–– Bio-regional.com free guide Reclamation led approach to
demolition
–– Deconstruction and reuse of construction materials, BRE
Hurley, J & others http://www.reuse-steel.org/
32 The Institution of Structural Engineers | Sustainability Briefings
Sustainability for bridge engineers – Part 1
Briefing Note 16
The Structural Engineer 89 (5) 1 March 2011
Figure 1 The Green Bridge, Mile End Road, London, designed by Mott MacDonald. It was constructed to reconnect public open spaces previously dissected by
roads and railways. The bridge carries park landscaping across a four-lane highway, providing a safe and uninterrupted pedestrian route as part of a 3km linear park
Introduction
Information on sustainability has largely been focussed on
environmental issues and reduction in carbon which has rightly
targeted transport and building operation. Currently sustainability
does not appear to form a major part of the day to day work of
a bridge engineer in the UK. This briefing note aims to illustrate
what engineers are already doing and how they might improve.
Knowledge of the subject is essential in order to provide good
advice to clients and provide a full professional service.
Bridge engineers are currently applying sustainability principles
within efforts to comply with CDM, design efficient structures and
minimise costs and disruption. They may not recognise all the
sustainable impacts or benefits of various options or understand
the issues that are particularly important and relevant to bridge
schemes. Applying sustainability principles will not change the
way work is carried out but will better inform decision making. For
bridge engineers the challenge is to learn a new language and
principles and to modify current practice rather than significantly
change it.
This briefing note is split into two parts. Part 1 gives a general
discussion and includes a list of issues to consider at project
inception. Part 2 gives lists of issues to consider at all other stages
of a project lifecycle. Reference to other briefing notes in this
series1 is recommended to understand the general principles.
What we are already doing
A significant majority of projects will already be subject to
environmental assessment, particularly if they are for Highways
Agency work. The environment is just one of the three pillars of
sustainability and environmental specialists cannot be expected to
address social and economic issues. The following points show
how current practice in bridge engineering already addresses
sustainability:
–– Application of CDM covers some social aspects
–– A design that minimises disruption to traffic results in savings
in fuel costs as well as social benefits
–– Minimising costs can also drive significant sustainable
benefits if it results in use of fewer raw materials. Minimising
interventions by strengthening or accepting load restrictions
rather than rebuilding a structure is also beneficial
–– Civil engineering applications already account for the majority
of recycled aggregates
–– Highways Agency area agents are already measuring carbon
on schemes and some are completing sustainability registers
–– Most major projects are subject to full sustainability
assessment which is tracked throughout the life of the
scheme through to construction and should be followed up
during operation and use
Measurement of environmental impact
Decision making in relation to sustainable choices will always rely
on judgement to balance social, economic and environmental
effects of any scheme. A number of measurement tools are
available. The relative merits of different measurements will
vary by location (the ratio of use of water: use of carbon will
have a different balance where water is scarce). Carbon and
sustainability measurement tools can be used to compare
options to inform decision making but should not be taken as
absolute measurements and results using different tools cannot
be compared. Some research is recommended before selecting a
The Institution of Structural Engineers | Sustainability Briefings 33
calculation tool because each will have limitations. Tools currently
available are:
–– Life cycle assessment2
–– ASPIRE, ICE (A Sustainability Poverty and Infrastructure
Routine for Evaluation)
–– CEEQUAL (Civil Engineering Environmental Quality
Assessment and Award Scheme)
–– Embodied energy and lifecycle tools (Environment Agency
calculator, Highways Agency)
–– CapIT & CESMM3 carbon price book
Engineering approach
The form of construction chosen has a significant impact on
how well a structure meets sustainability aims. The priorities for
a bridge engineer must always be to ensure that the structure is
safe to carry loads, serviceable for the intended use, durable for
the design life, and robust enough to accommodate damage and
the effects of maintenance and strengthening operations.
Engineers are ideally placed to manage the decision making
process for construction schemes. They must understand all
the issues within the sustainability agenda and the impacts and
benefits of alternative options, in order to provide comprehensive
advice to their clients and make reasoned decisions.
The increasingly litigious nature of society is leading to
conservatism and avoidance of risk which is working against
the aims for improving sustainability. The application of some
principles (e.g. arching action for bridge slabs) will involve more
design effort so the implications of this must be clearly explained
to the client.
It is often not appropriate to carry out a sustainability assessment
for minor bridge schemes but engineers should be recording
design decisions as they affect sustainable benefits and impacts,
possibly in a similar way to that used to record design decisions
for CDM.
Sustainability should be considered at every phase of a
development: planning, design, construction, maintenance,
change of use and demolition. The first and arguably the most
influential stage, planning or ‘project inception’ is expanded
below. Part 2 of this briefing note covers the remaining phases.
Project inception
Many key decisions are taken at an early stage and, since
bridges are generally very strategic structures with a long life,
a good understanding of sustainable issues is desirable. The
whole scheme lifecycle including modification and end of life or
replacement strategies should receive full consideration, both in
the brief and initial response.
At project inception consideration of sustainability should include:
–– the strategic contribution of the bridge to the locality
–– design and construction strategies
For significant schemes an overall contract strategy including
sustainability should be defined including reference to
performance specifications derived from an initial strategy and
needs assessment3. This stage is where much of the social and
economic impacts and benefits are determined.
34 The Institution of Structural Engineers | Sustainability Briefings
The following list includes references which illustrate examples of
good practice to address the two key points above. It is given as
a set of examples and should not be taken to be a comprehensive
checklist of all aspects of sustainability:
–– Guided public involvement in decisions4, public consultations
and presentations enhance local support
–– Provisions to inform travellers may reduce congestion and
objections
–– Provision for safety and operation of major bridges in extreme
wind, fog and ice particularly for users going underneath (e.g.
closures due to falling ice)
–– Resilience against severe damage and progressive collapse
of long crossings against accidental, natural and vandalism
damage
–– Resilience for climate change extreme weather events
–– The form of structure and method of construction should be
selected to minimise construction disturbance noise and dust.
–– Combining operations on a stretch of highway and avoiding
public events will minimise disruption
–– Combined use will enhance benefits e.g. utilisation of space
under a structure3; use of railway arches; green bridges (Fig
1); tunnels and cuttings may reduce noise and pollution
–– Selection of location to minimise environmental impact,
disruption and to maximise benefits. A good location will
minimise foundation size, span lengths and embankment
heights and will avoid sensitive sites and minimise land take
–– Improved transport links and the provision of integrated foot
and cycle provision are a benefit; foot and cycle bridges
encourage non-motorised use and new links can reduce
journey lengths
–– Plan the solution for the whole serviceable life including future
change or increase in use to suit need but avoid over design
–– Build in maintenance provision including access and
upgrading facility2
–– Detailed geotechnical investigations will facilitate efficient
design of foundations. Design can provide for some
foundation movements to minimise their size5
–– Early contractor involvement (ECI) can result in significant
benefits: buildability; waste management and reuse of
materials; minimisation of disruption
–– Building in a reduction in severance for wildlife by providing
green links, otter ledges etc
Part 2 of this briefing note provides detailed guidance for
consideration at the remaining stages of a project lifecycle.
References
1. IStructE Sustainable Construction Panel (2010) Sustainability
Briefing Notes 1-12. Available at http://www.istructe.org/
sustainability-briefing-notes (Accessed: 13 January 2011)
[Reprinted from The Structural Engineer 2008-2010]
2. Steele, Kristian: (2004) ‘Environmental sustainability in bridge
management’. BRE Information Paper IP14/04. Watford: BRE
Bookshop
3. IABSE. (1999) IABSE Symposium Rio De Janeiro 1999.
Structures for the future the search for quality. IABSE reports
v.83. Zurich: IABSE. [Keynote lecture & various papers on
sustainability]
4. Martin, A. J.: (2004) ‘Concrete bridges in sustainable
development’, Proc. Institution of Civil Engineers: Engineering
Sustainability, 157/4, p 219-230
5. Rowson, J.: (2009) ‘Thread lightly’, New Concrete Engineering
(Supplement to New Civil Engineer, October 22) October, p
22-23. [David Kreitzer Bridge, Lake Hodges, San Diego, USA]
The Institution of Structural Engineers | Sustainability Briefings 35
Sustainability for bridge engineers – Part 2
Briefing Note 17
Bridge scheme lifecycle
Sustainability should be considered at every phase of a
development: planning, design, construction, maintenance,
change of use (modification), and end of life (demolition) or
replacement. The first planning or ‘project inception’ stage is
discussed in Part 1 of this briefing and the rest of the stages
discussed below.
The Structural Engineer 89 (5) 1 March 2011
This briefing illustrates different approaches to meet sustainability
objectives at each stage of the project lifecycle. The points
covered here should be treated as ideas for consideration rather
than a comprehensive checklist. A full assessment is the only way
to understand the trade-offs and significance of each idea within
the context of a particular project.
The life cycle of a bridge as discussed below can be seen in the
context of CO2 emissions and global warming potential over its
life. In-use emissions associated with the design choices are traffic
diversions during maintenance, maintenance itself and finally,
demolition. Bridges have a long design life with relatively little
lifetime intervention so the initial impacts of the materials represent
a major proportion of the total lifecycle emissions. Therefore the
focus of design must be on providing a durable structure with
minimum initial impacts and minimum maintenance requirements.
Design
Anticipated impacts from every stage of the project need to be
considered during design:
Materials: A sustainable approach to materials will include
efficiency, responsible sourcing, design to minimise impacts,
healthy materials and consideration of end of life.
Efficiency: The materials used determine the amount of embodied
energy in a structure so raw construction materials and energy
should be minimised. This includes fabrication, transport and
construction energy. It has been shown that in general longer
span solutions for structures have higher material costs as well as
higher embodied energy1. ‘Architectural’ solutions which are not in
harmony with the structural form tend towards higher embodied
energy.
The quantity of raw materials can be minimised by using a
structural form with direct force transfer e.g. elements in pure
compression or tension, such as arch or stress ribbon bridges1, 2.
The use of compressive membrane action will minimise the steel
required in concrete decks (BD87/02). Use of reinforced soil in
place of RC walls minimises concrete volumes.
Use of innovative materials and forms can reduce the weight
of a structure. Lightweight structures minimise foundation size
and cost. For example: fibre composite materials3; engineered
cementitious composites4; bridge in a backpack5, timber and
rope6.
Strategies to minimise waste involve: design for reuse and
recovery, offsite construction, materials optimisation, waste
efficient procurement, deconstruction and flexibility7. Realistic
specification, repetitive details, good information and early input
from suppliers and contractor will make a significant contribution.
Balancing cut and fill increases material efficiency and reduces
construction impacts.
Responsible sourcing: Responsibly sourced materials are available
to the bridge engineer8. Recycled and secondary materials such
as aggregates, Portland cement replacements and tyre bales for
36 The Institution of Structural Engineers | Sustainability Briefings
embankment fill should be considered but balanced against
additional transport distances and technical requirements. (For
more information refer to previous sustainability briefings on
responsible sourcing, aggregate and a forthcoming briefing on
cementitious materials).
Design to minimise impacts: Optimisation on weight is not always
the most sustainable option. The material choice should be
evaluated against a full set of design constraints including cost,
environmental impact and durability. Very high strength concrete
can reduce material use9, however calculation is needed to show
that the weight saving offsets the increased embodied CO2 of
the material. Traditional methods such as masonry construction
can be more reliable when using local workforce. Options can be
compared using tools discussed in Part 1 of this briefing note.
Design for the full life cycle and health: Durable materials such
as concrete, galvanised steel, FRP and weathering steel avoid
the need to use coatings. An added benefit of the longer life
before maintenance of durable structures is the reduction in traffic
disruption and congestion.
In terms of longevity of a bridge, the capacity and condition of
bridge substructure will determine if a bridge life can be extended
through bridge deck replacement. The design requirements
for future proofing balanced against initial impacts merit careful
consideration. For elements of the bridge with a shorter design
life, use of materials or components that are easily recycled, such
as metal parapets, or reused, such as Bailey bridge components,
is an end of use benefit.
Material summary: Issues to consider are:
–– Avoid overdesign but not at the expense of future proofing
–– Prioritise the use of local raw resources and construction
methods
–– Minimise transport distances and consider suitable size of
elements for delivery to the site
–– Responsible sourcing for concrete and timber
–– Design for balanced earthworks cut and fill
Water and pollution: Water should be addressed at the design
stage and in particular the use of water should be minimised as a
resource. The designer should also consider drainage provision,
water attenuation and catchment and groundwater resources. A
sustainable scheme will enhance catchment and minimise runoff
to reduce flood risk.
Construction
Early contractor involvement in design (ECI) provides an
opportunity to reduce construction impacts. Contractor and
supplier input can help develop realistic specifications particularly
if extreme exposure and workability is required. The designer can
consider ease of access with possible advance enabling works to
avoid overrun and delays. Protection from groundwater pollution
during construction and in use can be achieved by installing reed
beds or petrol interceptors.
ECI will facilitate early discussion of a site waste management
plan for waste reduction10. The contractor can avoid waste
by ordering pre-cut or prefabricated elements and deploying
reusable shuttering or slipforming. This also helps to minimise
construction time and improve quality. Quality assurance and
control procedures are important tools. Close site supervision
will avoid mistakes and rework together with proper storage and
site control to avoid damage. Good survey information leads to
accurate setting out. Good information for estimating and ordering
materials for site helps avoid oversupply and facilitates the design
of elements to fit without need for cutting.
Maintenance and use
Congestion has a very high sustainability cost directly in fuel
use but also in social and economic terms. This can influence
the choice on whether to replace or strengthen a structure. The
following list provides examples of how this can be minimised at
initial design stage:
–– Provision of access for maintenance without disruption to
traffic or services
–– Define emergency procedures for major crossings
–– Provision for replacement of limited life elements. Easy
removal will allow remedial works to a better quality offsite,
e.g. provision of jacking points for bearing replacement
–– Design to allow replacement, widening or strengthening
while maintaining the structure in service. Steel structures are
generally easier to strengthen
–– Design for robustness or provide generous headroom to
avoid damage particularly for steel beams which are more
vulnerable to impact damage. Provision of protection or
warnings to prevent damage
–– Minimise future maintenance requirements: integral bridges
with no joints or bearings; good detailing to avoid problems
(water path)
Once the bridge is in-use the following examples demonstrate
material efficient approaches to maintenance:
–– Innovative testing methods to prove structural adequacy or
provide accurate estimate of remaining life. Proof load testing11
–– Relaxed assessment criteria, an accepted departure from
standard such as load restrictions or use of less conservative
analysis methods, reduce or avoid the need to strengthen or
replace. For example, compressive membrane action can be
utilised to improve capacity of slab decks BD44/95
–– Regular preventive maintenance
–– Innovative repair or strengthening options e.g. carbon fibre or
heat straightening12
Demolition
Demolition should be considered carefully for temporary
structures, and a Sustainability Briefing on Design for
deconstruction published in The Structural Engineer, 89/4, gives
more information on this. Use of materials or components that are
easily recycled or reused, such as aluminium parapets and bridge
components, is an end of use benefit, e.g. Bailey bridges have
significant reusable elements.
References
1. Long, A. E. et al.: ‘Sustainable bridges construction through
innovative advances’. Proc. ICE – Bridge Engineering, 161/4,
December 2008, p. 183–188
4. Chandler, R. F.: ‘Life-cycle cost model for evaluating the
sustainability of bridge decks’. Report No. CSS04-06 2004.
University of Michigan Center for Sustainable Systems
5. Bridge in a Backpack, Advanced Infrastructure Technologies
6. McGlade, D.: Carrick-a-Rede rope bridge, The Structural
Engineer, 87/14, 21 July 2009, p. 21–26
7. WRAP web site ‘Designing out waste in civil engineering’ tools
and guidance
8. BRE Environmental & Sustainability Standard. BES 6001:
ISSUE 2.0 Framework Standard for the Responsible Sourcing
of Construction Products
9. Martin, A. J.: ‘Concrete bridges in sustainable development,
Proc. ICE – Engineering Sustainability, 157/4, December
2004, p. 219–230
10.Wrap web site ‘site waste management’ tools and guidance,
available at: http://www.wrap.org.uk/construction/tools_and_
guidance/site_waste_management_planning/index.html
11.Clubley, S. K. et al.: ‘Load distribution of bridge parapet
supports in southern England: Re-evaluation, testing and
analysis’. Engineering Failure Analysis 14, 2007
12.Clubley, S. K., Winter, S. N., Turner, K. W.: ‘Heat straightening
repairs to a steel road bridge’, Proc. ICE – Bridge
Engineering,159/1, March 2006, p. 35–42
Bibliography
–– Collings, D.: (2006). ‘An environmental comparison of bridge
forms’. Proc. Institution of Civil Engineers, Bridge Engineering,
159/4, p. 163-168
–– Daniel, R. A.: ‘Environmental considerations to structural
material selection for a bridge’. European Bridge Engineering
Conf. Lightweight Bridge Decks, Rotterdam, Netherlands,
2003
–– Itoh, Y. and Kitagawa, T.: (2003). ‘Using CO2 emission
quantities in bridge lifecycle analysis’. Engineering Structures,
25/5, p. 565-577
–– Pacheco, P., Adao da Fonseca, A. P., Resende, A. and
Campos, R.: (2010). ‘Sustainability in bridge construction
processes’. Clean Technology and Environmental Policy, 12,
p. 75-82
–– Steele, K., Cole, G., Parke, G., Clarke, B. and Harding, J.:
(2003b). ‘Highway bridges and environment – sustainable
perspective’. Proc. ICE, Civil Engineering, 156/4, p. 176-182
–– Willetts, R., Burdon, J., Glass, J. and Frost, M.: (2010).
‘Fostering sustainability in infrastructure development
schemes. Proc. ICE, Engineering Sustainability, 163/3, p.
159-166
–– Zhang, C.: (2010). ‘Delivering sustainable bridges to help
tackle climate change’. Proc. ICE, Engineering Sustainability,
163/2, p. 89-95
2. Agrawal, R.: ‘Stress ribbon bridges’, The Structural Engineer,
87/22, 17 Nov 2009, p.22–27
3. Head, P. C.: ‘New bridge technology for sustainable
development’, Proc. ICE, Bridge Engineering, 157/4,
December 2004, p.19–202
The Institution of Structural Engineers | Sustainability Briefings 37
Cementitious materials
Briefing Note 18
The Structural Engineer 89 (9) 3 May 2011
In the context of the need to consider whole life performance and
the interdependence of operational and embodied carbon dioxide
(ECO2), there is increasing pressure on structural engineers
to specify materials in a manner that minimises environmental
impacts even if those materials are abundant. This briefing note
seeks to give guidance on how this can be achieved with cements
and combinations whilst avoiding unforeseen consequences
which lead to a less sustainable outcome. Cements are single
powders supplied to concrete producers containing, for example,
Portland cement and fly ash. Combinations are formed where
concrete producers mix Portland cement with, for example, fly
ash in a concrete mixer.
Background
The materials commonly used with Portland cement are ground
granulated blastfurnace slag (GGBS), siliceous fly ash, silica fume
(all industrial by-products from other industries) and limestone.
Durability of concretes can be improved by the use of these
materials and this benefit is recognised in codes of practice.
Common proportions of GGBS, fly ash, silica fume and limestone
fines used in UK-produced combinations are 50%, 30%, 10%
and 6-10% by mass of total cementitious content respectively,
and the use of these pre-dated the current sustainability agenda
due to cost and performance credentials.
For most applications and construction scenarios, BS 8500-11
allows considerable specification flexibility in terms of cement or
combination type used. Permitted Portland cement replacement
ranges, by mass, are 6-10% (silica fume), 6-20% (limestone),
6- 55% (fly ash) and 6-80% (GGBS). The British Standard
table A.6 in BS 8500-1:2006 provides details of the cement
and combination types recommended for UK structures where
selected exposure classes, intended working life and nominal
cover to normal reinforcement have been identified.
The British Standard does not give specific guidance on the
relative merits of cements and combinations in terms of their
associated performance (apart from that relating to exposure) and
environmental impacts. This briefing provides initial guidance on
these matters.
Concrete
Concrete
type
ECO2 (kgCO2/m3)
CEM1
30%
concrete fly ash
concrete
50%
GGBS
concrete
173
124
98
184
142
109
318
266
201
315
261
187
RC40
Structural:
in situ floors,
70mm
superstructure, walls,
basements
372
317
236
High strength
concrete
436
356
275
Blinding, mass fill,
strip footings, mass
foundations
GEN1
Trench foundations
GEN1
70mm
120mm
Reinforced
foundations
RC30
Ground floors
RC35
70mm
70mm
RC50
70mm
Table 1 ECO2 for different concretes (Data source: www.concretecentre.com)
38 The Institution of Structural Engineers | Sustainability Briefings
Embodied carbon and recycled content
Use of fly ash, GGBS and silica fume, by-products/waste from
other industries, contributes to the recycled content of the final
concrete. Also their use will directly reduce the ECO2 of the final
concrete. Table 1 shows the ECO2 for different concretes based
on UK production. (Note CEM1 is the designation for 100%
Portland cement).
When designating or designing concrete to BS 8500-1:2006,
close attention should be given to all of the strength classes
and cement/combination types permitted for selected
minimum working lives, exposure classes and nominal covers
to normal reinforcement. Giving preference to options with low
recommended minimum cement contents and permitted cement/
combination types with the highest levels of Portland cement
replacement will directly reduce values of ECO2 of the concrete
and increase recycled contents.
It is important to note that ECO2 or recycled content values for
concrete should not be considered or specified in isolation.
Adopting holistic approaches to sustainability-related decision
making is always advisable, given the significant impact of
cement/combination type and content on a range of key concrete
properties given below.
Early strength development/heat development
For a given value of 28 day strength, concrete containing
additions such as fly ash and GGBS will exhibit lower relative early
age strengths and lower heat development, than those containing
Portland cement only. This is because concrete’s early strength is
dependent, primarily, on its Portland cement content. However it
is likely that some level of additions will be possible in most cases.
Recognised routes to address low early strength gain for low
ECO2 concretes are available. To help reduce formwork striking
times, for instance, technologies such as accelerating admixtures
can be combined with increased insulating effectiveness of
formwork and accelerated application of curing.
Equally, established methods2,3,4 for more accurately determining
in situ early age concrete strengths and/or formwork striking times
are available. These include the use of maturity methods using
site specific or predicted input data; on site cured or temperaturematched test cubes; and penetration, pull-out or break-off tests.
Contractors are able to erect concrete structures, such as framed
buildings, conventionally (to programme and budget) using low
ECO2 concrete mixes. Indeed, using the established assessment
techniques described above, innovative construction teams are
presently erecting high rise structures year round using average
to high Portland cement replacement levels with additions such
as fly ash and GGBS. In the UK further details may be sourced
from CONSTRUCT and British Ready Mixed Concrete Association
members.
Reduced heat development is an advantage for large cross
section elements and can be achieved through the use of GGBS,
fly ash, limestone fines or silica fume thus reducing thermal
gradients and the risk of cracking.
Colour
The surface colour of concrete is dominated by its finest
particles, which typically includes the cement/combination
and sand particles smaller than around 63μm. The colour of
Portland cement varies, according to the materials from which
it is manufactured. The incorporation of additions such as fly
ash, GGBS and micro silica also has a major influence. GGBS
Figure 1 Pale off white finish of GGBS
Figure 2 Dark grey finish of fly ash
is off-white in colour (see Figure 1) and substantially lighter
than Portland cement due to its low iron content. Fly ash is
dark grey in colour (see Figure 2), resulting from a combination
of iron compounds present and carbon residues left after the
coal is burned as part of its manufacturing process, the shade
depending on the source of coal and the process plant used.
Where structural aesthetics are critical, the impact of cement/
combination type on concrete colour may dominate over
restrictions due to local availability or requirement for ECO2
content. Further guidance5,6 on cement/combination type and
concrete colour is available in the literature.
Availability
Fly ash and GGBS are widely available in the UK and transport
distances from the point of production to the point of use are
similar to that for Portland cement. At ready-mixed concrete
plants producers typically stock Portland cement and either
GGBS or fly ash. Limestone fines and silica fume may also be
available in a percentage of ready-mixed concrete plants, or
be made available given sufficient notice, but will not always be
available at all locations. As such, overly prescriptive specifications
that dictate a firm requirement for fly ash, GGBS, limestone
fines or silica fume may not lead to economical and/or more
sustainable solutions. Instead, the recommended approach is to
prepare specifications that allow flexibility and choice in terms of
materials, with, perhaps, caveats added to state justified material
preferences. Advice is given in the 4th edition of the UK National
Structural Concrete Specification7. Beyond the UK, advice with
respect to availability should be sought from relevant trade
associations or local concrete producers.
References
1. BS 8500-1:2006 Concrete – Complementary British Standard
to BS EN 206-1. Part 1: Method of specifying and guidance
for the specifier, BSI
2. A Decision Making Tool for the Striking of Formwork to
GGBS Concretes (a project report submitted for the award of
Diploma in Advanced Concrete Technology, The Institute of
Concrete Technology), John Reddy, 2007
3. Clear, C. A.: ‘Formwork striking times of ggbs concrete: test
and site results’, Proc. Inst. Civ. Eng., Structures & Buildings,
1994, 104, Nov., p 441-448
4. Formwork striking times – criteria, prediction and methods of
assessment, CIRIA Report 136, TA Harrison, 1995.
5. Architectural Insitu Concrete, RIBA Publishing, ISBN 978 1
85946 259 1, David Bennett, 2007
6. Plain formed concrete finishes, Technical report 52, The
Concrete Society, 1999
7. CONSTRUCT, National Structural Concrete Specification for
Building Construction 4th edition, April 2010, The Concrete
Centre, available at: http://www.construct.org.uk/media/
National_Structural_Concrete_Specification_for_Building_
Construction.pdf
The Institution of Structural Engineers | Sustainability Briefings 39
Climate change and wind speeds
The Structural Engineer 89 (10) 17 May 2011
The principal meteorological hazards in tropical and sub-tropical
regions are high winds, rainfall, wind-driven waves and storm
surge. The hazards of waves and storm surge are related to wind
speeds. With increases in speeds it is reasonable to conclude that
waves and storm surge will pose more intense threats in coming
years. These threats will be further amplified by rising sea levels.
Most of the economic activities of many tropical islands are
located in coastal areas. Therefore the issues of global warming,
rising sea levels, increased wave energy, more severe storm
surge and increased wind speeds are of critical importance to the
long-term sustainability of the economies of such regions. As a
consequence, structural engineers living and working on projects
in such regions have a vested interest in all efforts worldwide to
mitigate anthropological-induced climate change. Torrential rains
may be affected by climate change. However, this issue is not
associated with wind speeds.
Reference is made to the UK’s Technology Strategy Board report
‘Design for Future Climate – opportunities for adaptation in the
built environment’1. In it is mentioned the Association of British
Insurers recommendation that design codes for buildings in the
south east of the UK should incorporate increased wind speeds,
although the document indicates that the effect of climate change
on future wind loading is unclear.
Climate change
Hurricane Catarina made landfall in the north of Brazil on 27
March 2004. This was the first hurricane ever recorded in the
South Atlantic. Hurricane Ivan struck the island of Grenada on
7 September 2004 with peak gust winds of 135mph (60ms–1).
According to the USA National Hurricane Centre, Ivan was ‘...
the most intense hurricane ever recorded so close to the equator
in the North Atlantic’. On 30 August 2008 a new world surface
wind gust record for hurricanes was registered at the Paso Real
de San Diego meteorological station in Pinar del Rio (Cuba)
during Hurricane Gustav. The Dines pressure tube anemometer
recorded a gust of 211mph (94ms–1). Are these isolated incidents
or portents of future climate?
In 2008 the World Bank funded a multi-faceted project of which
one component was the investigation of the possible effects of
climate change on wind speeds for structural design in the island
of St Lucia in the Eastern Caribbean. The project was executed
by the Caribbean Community Centre for Climate Change and
the actual work was done by the International Code Council (a
wholly USA organisation) using the services of Georgia Institute
of Technology (principal researchers Judith Curry and Peter
Webster), Applied Research Associates Inc (principal researcher
Dr Peter J. Vickery) and Tony Gibbs.
Hurricane activity in the North Atlantic (including the Caribbean)
follows multi-decadal cycles. The current warm phase of the
Atlantic multi-decadal oscillation is expected to extend to the year
2025. By that time it is expected that the sea-surface
40 The Institution of Structural Engineers | Sustainability Briefings
16
14
28.5
Warm AMO
*
12
10
28
27.5
8
6
27
4
2
0
1945
1970
Year
1995
Sea Surface Temp. °C
Meteorological hazards and long-term sustainability
#Tropical Cyclones
Briefing Note 19
With basic wind speeds for conventional buildings in Saint Lucia increasing by about 12-14%
with a corresponding 25-30% increase in forces, national codes are being revised. This raises the
question of whether national codes in other countries may be based on out-of-date wind speeds
2020
Figure 1 North Atlantic Tropical Cyclones and SST – Decadal scale variations:
9-yr Hamming filter. (Courtesy of Judith Curry, Georgia Institute of Technology)
temperatures would have risen by 1°F (0.56°C). The region
experiences historically more hurricanes, and more severe
hurricanes, during warm phases of Atlantic multi-decadal
oscillations.
The number of tropical cyclones in the North Atlantic have
averaged 10/year in the past 50 years and 14/year in the past
decade, see Figure 1. This is projected to rise to 15-20/year
by 2025. The combination of greenhouse warming and natural
cyclical variability of the climate will produce unprecedented
tropical cyclone activity in the coming decades.
Historical background
During the past 50 years, the evolution of wind speeds for
structural design in the Commonwealth Caribbean (which consists
of 17 former (and current) British colonies in the Caribbean) is as
follows:
–– Early 1960s – CP3: Chapter V: Part 2:1952 (This did not
address hurricane force winds)
–– Mid to late 1960s – South Florida Building Code (The
procedures were very elementary.)
–– 1970 – the first Council of Caribbean Engineering
Organisations (CCEO) standard. (This followed the philosophy
of the then yet to-be published CP3: Chapter V: Part 2: 1972.
The meteorological work was done by Harold C Shellard,
formerly of the UK Meteorological Office and attached to the
Caribbean Meteorological Institute 1967-70.)
–– 1981 – Revision of the CCEO standard (It has since been
adopted as the Barbados standard BNS CP28. The
meteorological work was done by Basil Rocheford of the
Caribbean Meteorological Institute (now Caribbean Institute for
Meteorology and Hydrology).)
–– 1985 – Caribbean Uniform Building Code (CUBiC) Part
2: Section 2 (The meteorological work was done by Alan
Davenport, Dr David Surry and Dr Peter Giorgiou of the
Boundary Layer Wind Tunnel Laboratory, University of
Western Ontario.)
Increase in basic wind speed
Category II Buildings
Category III and IV Buildings
Figure 2 Percentage increase in basic wind speed in St. Lucia vs. percentage
increase in annual rates of Category 4 and 5 hurricanes. Based on work of Dr
Peter Vickery of Applied Research Associates
–– 2008 – Caribbean Basin Wind Hazard Study. (The principal
researcher was Peter Vickery with D Wadhera of Applied
Research Associates, Inc.) Tony Gibbs was directly involved
with all of the listed work from 1969-70 to the present.
Effects on wind speeds
For conventional buildings (i.e. Category II in the American Society
of Civil Engineers standard ASCE 7) the proposed Caribbean
standard (based on ASCE 7) will adopt a 700-year return period
wind speeds and for important buildings (i.e. Categories III and
IV in ASCE 7) the 1700-year return period wind speeds will be
adopted. (These return periods provide ‘ultimatep’ or failure wind
speeds.)
There could be an average of three to four Category 4 and 5
hurricanes per year by 2025 in the North Atlantic (note these
categories are of the Saffir-Simpson scale for hurricanes, not to be
confused with the building categories in ASCE 7). This incidence
of hurricanes represents a 210 to 280% (average 245%) increase
in the number of Category 4 and 5 hurricanes compared to
the long-term (1944-2007) average of 1.4 Category 4 and 5
hurricanes per year. If this turns out to be the case, the basic
wind speeds for conventional buildings in Saint Lucia would be
increased by about 12 to 14% (25 to 30% increase in forces), and
the basic wind speeds for important buildings would be increased
by about 10% (21% increase in forces). See Figure 2.
Although the studies were carried out specifically for St Lucia, the
results are probably valid for most of the Eastern Caribbean and
are generally indicative of what is in store for much of the North
Atlantic. This work carries an important message for all countries.
Serious consideration should now be given to modifying wind
speeds in other countries where national codes may be based on
out-of-date wind figures.
References
1. Technology Strategy Board, Design for Future
Climate – opportunities for adaptation in the built
environment, available at: https://www.innovateuk.org/
documents/1524978/1814018/Design+for+future+climate++opportunities+for+adaptation+in+the+built+environment/65a
eb874-12f2-46aa-a887-14e6f980c006
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