ARCHITECTURE Low-carbon concrete
Affordable, low-carbon concrete is
now a reality
Article by Jennifer Wagner, Vice President of Sustainability CarbonCure Technologies
M
ost people have heard that concrete has a relatively high carbon footprint. This applies
to all types of concrete, which includes concrete masonry, precast and ready mix. With
mounting pressure from end users to reduce concrete’s carbon footprint, the entire concrete
industry is now responding and is looking for new strategies to reduce its footprint. These strategies
can include new materials, technologies and processes to minimise CO2 emissions during production
or approaches to actually absorb CO 2 into the material. Let’s start by discussing the source of carbon
emissions in the industry, and then address some of the solutions.
You might be wondering what the major sources of CO 2 are in the cement and concrete industry.
The majority of the carbon footprint of concrete is actually attributed to CO 2 produced during cement
production. Cement acts as the glue that holds concrete together, and is a critical ingredient in
concrete. The production of one tonne of cement creates up to 0.8 tonne of CO 2, making the carbon
intensity of cement production the biggest environmental impediment for the concrete industry.
There are two main sources of CO 2 emissions associated with cement production: 1. Fuel combustion – required to heat the raw materials of cement to high temperatures, and
2. Calcination – CO 2 is released during a chemical reaction that takes place during cement
production.
For the chemistry buffs out there, here is the science behind the reaction:
Jennifer Wagner
1. When cement is produced, the raw material (limestone) is heated to produce lime (CaO), a precursor to cement – this reaction is
known as calcination and releases a molecule of CO 2
CaCO 3 (limestone)
CaO (lime) + CO 2
Cement production is ultimately responsible for about 5 percent of global carbon dioxide emissions. These emissions might not be
a problem if there wasn’t so much cement and concrete manufactured globally. According to the IMF database world economic outlook,
worldwide cement consumption reached a record estimated 3.6 billion tonnes in 2012. Future forecasts show that production will increase
even higher owing to growing demand in developing markets. This also translates into increased demand for concrete. In fact, concrete is
the world’s most widely used building material with about one tonne of concrete used per person every year.
The good news is that strategies are available to reduce the CO 2 footprint of concrete. In fact, a recently published paper [1] by Licht and
colleagues in Chemical Communications entitled “STEP cement: Solar Thermal Electrochemical Production of CaO without CO 2 Emission”
hints of a future where cement can be produced with zero carbon emissions [2] and therefore potentially yield carbon negative concrete
products. This would be an important development for the industry and for the environment, given that cement and concrete production
is on the rise.
Here are some of the options available today to make lower-carbon concrete products; most of the efforts have been in developing
lower-carbon cement, which in turn would yield concrete products with a lower carbon footprint. The cement industry has three realistic
avenues to reduce the carbon intensity of cement (and thereby improve the sustainability profile of concrete):
1. Thermal and electrical efficiency - Deploy best available technology in new cement plants (while pursuing retrofits where
economically viable) to lower the energy requirements for producing cement,
2. Alternative fuels - Use less carbon-intensive fuels and/or alternate fuels to supply the energy for cement production, and
3. Clinker substitution - Substitute clinker (a precursor to cement) with other low carbon materials with “cementitious” (i.e. cementlike) properties, for example fly ash or slag.
To contextualize these efforts, currently clinker substitution can help achieve LEED points since it contributes to the recycled content credit.
Other cement and concrete industry carbon intensity levers currently do not provide additional LEED points. Luckily, future versions of
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Low-carbon concrete ARCHITECTURE
LEED (such as the upcoming LEED v4) are likely
to reward environmental efforts within the
cement and concrete industry by issuing points
for manufacturers who provide Environmental
Product Declarations (EPDs). EPDs are tools
used to measure the environmental impact
of a produc t throughout its entire life
cycle.
A unique idea developed by Canadian
innovator CarbonCure Technologies involves
taking waste carbon dioxide (CO2) and injecting
it into concrete during production. The concept
is to use a new mineral carbonation technology
for beneficially reusing waste CO 2 in the
concrete products’ manufacturing process –
or simply put, recycling waste CO 2 to make
greener concrete. The company was founded
in 2007 by Robert Niven, who put his chemistry
and engineering background to work when he
developed the technology and brought the
idea out of the lab and into the real world. Niven’s idea of using sequestering CO 2 in concrete production to make concrete stronger and
greener was developed from the understanding of earlier uses of CO 2 in concrete production in the 1940s. CO 2 was used in the early days
primarily to protect against freeze-thaw and efflorescence, and the mechanism is well understood. Niven simply developed a technology
that overcame some of the engineering challenges associated with early technologies that used CO 2.
The success to date of CarbonCure can be attributed to Niven’s strong team and extensive list of industry partners. Niven’s ultimate
goal is to work with other material and technology innovators to eventually bring affordable low-carbon concrete products to market. Since
then, the company has built durable industry partnerships with leading concrete products manufacturers across North America, including
Shaw Group, the largest concrete products company in Atlantic Canada that has been working with CarbonCure for the past five years.
There are several environmental advantages to using CarbonCure’s technology in the manufacturing process. CarbonCure’s technology
delivers waste CO 2 into concrete masonry products while it’s being manufactured. The CO2 gas undergoes a chemical reaction and is
converted into a solid - calcium carbonate – within the concrete. This means that CO 2 - which would have otherwise become a harmful
greenhouse gas - now becomes safely and permanently embedded in the concrete. The introduction of CO 2 can also create other material
advantages for the manufacturer, such as higher early strength of the concrete. This higher early strength can translate into lower cement
and energy requirements, reduced defects (solid waste) and other manufacturing benefits. The best part is that the products don’t have
a significant cost premium – CarbonCure products cost about the same as regular concrete products. The products also meet all required
ASTM and CSA standards. The bottom line is that products made with CarbonCure’s technology are green without the tradeoffs.
CarbonCure works with concrete products manufacturers to introduce
its CO 2-injecting technology into their plants. CarbonCure is currently working
with several manufacturers across North America to bring low-carbon concrete
products to market. Current manufacturing partners include Shaw Group
(Eastern Canada), Atlas Block (Ontario), Northfield Block (Illinois) and Basalite
(Northern California). CarbonCure also engages with end users to encourage
adoption of green concrete in the market. Several architects, engineers and
construction firms (AECs) have already specified CarbonCure products for
construction projects. The designers wanted sustainable products that meet
all performance criteria and specified CarbonCure concrete masonry across
all construction projects at their firms.
The building sector will continue to push the limits on green, with the
emergence of LEED v4, the Living Building Challenge and Architecture 2030.
For instance, Architecture 2030 is challenging manufacturers to reduce their
product’s carbon footprint by 50 percent by the year 2030. By combining several innovative approaches such as CarbonCure’s technology,
the concrete industry will be well positioned to meet the growing demand for low-carbon building materials.
Moving forward, CarbonCure is looking for partners to help transform the built environment by manufacturing and building with
low-carbon concrete wherever possible. Imagine a future where concrete absorbs more CO 2 than was emitted during its production. While
we aren’t there yet, we certainly are headed in the right direction. With a commitment to continued innovation, this technology is the
company’s first step towards integrating and developing affordable regenerative concrete at scale. For more information, email Jennifer
Wagner at [email protected] or visit www.carboncure.com.
[1] http://pubs.rsc.org/en/content/articlelanding/2012/CC/C2CC31341C#!divAbstract
[2] http://phys.org/news/2012-04-solar-thermal-cement-carbon-dioxide.html
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