| Concrete restoration | Concrete surface protection in traffic structures |
Deep impregnation
Preventive surface protection of
reinforced concrete structures
The information in this brochure represents the knowledge available to us at present and is based on many years of experience and comprehensive testing. The
information is intended to supplement the guidelines for application and technical data sheets. Due to the comprehensive scope of applications and techniques
involved, we are unable to guarantee the validity of the information in all instances. Our systems and products are subject to ongoing development and we
reserve the right to effect modifications for technical and legal reasons. Please refer to our internet site www.stocretec.de or your StoCretec systems consultant
for our latest technical information. This brochure will cease to apply upon publication of a new edition.
Contents
Reinforced concrete needs protection
Reviving ancient knowledge
4
Reinforced concrete and chlorides
A problematic relationship
6
Ecology and economy
Facts and figures
8
Deep impregnation of concrete in detail
Protection of concrete with the aid of chemistry
10
Planning and site execution
A method as simple as it is efficient
12
One step ahead
A forward-looking approach to protection
in Sweden
14
Reinforced concrete needs protection
Reviving ancient knowledge
Reinforced concrete is an excellent construction media, anything
but permanent – a fact underlined
by the current figures on damage
to buildings and the resultant
increase in repair measures.
Hydrophobization is not a modernday invention – it was used by the
Romans 2000 years ago. The Mayans
also knew that stone facades could
be made more durable by adding
natural fats and oils.
Ecologically and economically
acceptable preservation measures are
available, providing buildings with
sustained protection by means of
manageable technical processes. One
excellent method is through deep
impregnation of reinforced concrete
structures. This technical surface
treatment process has already been
carried out on many different buildings as a means of preventing the
capillary intake of aqueous saline
solutions, aggressive to concrete.
Successful practical experience over
12–15 years demonstrates the
effectiveness of this method.
Hydrophobization evolved into deep
impregnation, driven by the results of
modern research. Today, the deep
impregnation of cement-bound
building components represents one
of the most effective protective measures to prevent harmful
substances dissolved in water from
entering into the concrete surface
zone.
The master builders knew
how to protect their
buildings back in ancient
Roman times. As the
lasting results show ...
Reviving ancient knowledge with modern
chemistry: Surface protection for reinforced concrete structures.
4 | Reinforced concrete needs protection
Reinforced concrete needs protection | 5
Reinforced concrete and chlorides
A problematic relationship
6 | Reinforced concrete and chlorides
Once the chloride front
reaches the reinforcing
steel, rust forms.
The resultant increase in
volume causes the con-
Reinforced concrete structures
forming part of our infrastructure,
such as motorway and railway
bridges, are particularly exposed
to the most diverse environmental
influences. Sooner or later, these
take their toll in the form of
corrosive damage and a curtailed
service life.
Concrete is a porous material
produced from cement, aggregate
(e. g. sand or gravel), water and
sometimes other additives. Cement
reacts with water to form a hardened
paste which bonds the aggregate
content to produce the composite
material concrete. Cement-bound
materials have a highly ramified pore
system which is able to take up
fluids quickly and in large quantities
by means of capillary action. The
so-called concrete surface zone
(up to 3 cm from the surface) differs
markedly from the core concrete. In
addition to higher porosity, this outer
zone is also more permeable to gas
and water.
crete covering the steel to
flake off and reinforced
concrete components
threaten to lose their
load-bearing capacity.
According to the ambient conditions
and the form of use, chlorides – from
de-icing salt solutions or sea water,
for example – are transported via the
capillary pores of the hardened
cement paste into the concrete
surface zone. When a critical chloride
level is exceeded in the reinforced
concrete and appropriate reactants
are present (e.g. sufficient supply of
oxygen and appropriate moisture
conditions), reinforcement corrosion
occurs.
This causes the covering concrete
to flake off, exposing the reinforcing
steel.
Cement crust
Core concrete
Many damage mechanisms, such
as chloride-induced reinforcement
corrosion, are associated with the
transport of water in the concrete
surface zone.
Concrete surface zone
Mortar surface zone
Reinforced concrete and chlorides | 7
Technological aspects
For repair purposes, the defective
boundary-zone concrete needs to be
removed down to the reinforcement.
The steel has to be cleaned and
provided with a corrosion-proofing
agent. The existing concrete is then
reprofiled. The application of new
concrete to old concrete results in a
new interface. If the two materials
are not perfectly matched, practical
experience shows that damage may
recur after only a few years.
Economical aspects
Studies have shown that the cost of
repairing such bridge piers is many
times higher than the original cost
of producing the pier. The direct cost
of repairing a pier stands at around
€ 30,000. The traffic control costs
can amount to around € 100,000
to € 120,000. This figure does not
include the indirect congestion costs
(e. g. additional fuel consumption,
extended journey times and the
negative consequences for the
economy).
Ecological aspects
In addition to the high financial costs,
repair measures are generally of a
highly energy- and resource-intensive
nature. As a result, they sometimes
have a significant ecological impact.
It has been established that a repair
measure may involve three times the
environmental impact pertaining to
original production of the structural
component concerned (e. g. pier).
Comparison of repair and deep impregnation
by reference to the example of a bridge structure, service period 25 years
100
Relative ecological impact (%)
Central supports on bridges built over
motorways are an example of structural components facing a particularly
high level of risk. These central supports are exposed to splash water
containing de-icing salt which leads
to high chloride loads in the winter
months. These high chloride loads
consequently induce severe corrosion
damage in the reinforced concrete in
the shortest of time. Extensive and
costly repair measures entailing a
high level of environmental impact
then become necessary.
80
60
40
20
11%
1%
Energy
4%
Greenhouse
effect
1%
Soil
acidification
Repair
Smog
formation
Ecotoxicity
Deep impregnation
Ultra-high-pressure water jet treatment
Sand-blasting and corrosion-proofing
Shotcreting incl. subsequent treatment
8 | Reinforced concrete and chlorides
1%
Deep impregnation incl.
product manufacture
Environmental impact of
long-term degradation
Release of ethanol during
film formation
An example
A bridge construction originally
designed for 100 years of use without
repairs needs to be repaired after 25
years. The attendant environmental
impact has been assessed in an ecological balance (see graph on page 8).
The environmental impact of deep
impregnation is shown in the same
graph for the purposes of comparison. These figures show that deep
impregnation can be carried out up
to nine times before the ecological
consequences of the two measures
(smog formation) attain comparable
levels. This means that when carrying
out repair after 25 years, deep
impregnation would have to remain
effective for a minimum period of
around 3 years in order to attain
ecological viability. In actual fact according to information currently available, deep impregnation remains
effective for around 15 to 20 years.
This has economical consequences. If
the structure had undergone effective
deep impregnation at regular intervals from the time of its original completion, the damage could have been
avoided. A comparison of the repair
costs with the investment required for
effective preventive deep impregnation enables an assessment of the
minimum period of effectiveness
required for a waterproofing measure, in order to render it economically viable.
The interest on the capital invested in
repair and deep impregnation respectively must also be considered. The
minimum required period of effectiveness for a deep impregnation measure can be determined from the
comparison of the respective levels of
capital expenditure on the basis of
different interest rates. At interest
rates from 4 to 6 %, carrying out
deep impregnation every 7 to 11
years is more than economical if, as a
result, the need to carry out repair
after 25 years can be avoided.
35 years
Minimum required effectiveness
of deep impregnation
Preventive surface protection by
means of deep impregnation provides
an effective means of preventing such
damage from the outset.
11 years
7 years
4%
6%
8%
Interest rate
Reinforced concrete and chlorides | 9
Deep impregnation in detail
Protection with the aid of chemistry
Deep impregnation involves
impregnating a mineral building
material to render it waterrepellent. In order to classify the
levels of stress to which reinforced
concrete structures are exposed
and the necessary protective measures, a three-level concept has
been evolved on the basis of the
“effective penetration depth”. This
value represents the thickness of
the concrete surface zone in which
the active content in the waterrepellent agent is sufficient to
completely prevent capillary water
absorption.
For practical purposes, the three-level
concept is applied to assess the stress
situation and the relevant waterproofing requirements. Suitable products
are then selected on the basis of this
classification:
Level 1 u Priming
When using surface protection systems (OS 2) the substrate is primed
with a waterproofing agent. The
products employed for this purpose
attain an effective penetration depth
of approx. 1-1.5 mm. Either so-called
silicone microemulsion concentrates
(StoCryl GW 100) or solvent-diluted
systems with an active content level of
< 20 % (StoCryl HP 100) are used.
10 | Deep impregnation in detail
Level 2 u Mist zone
This level first and foremost covers
building elements which are exposed
to high levels of chloride, such as
bridge abutments. Examples of products employed for this level include
highly viscous water-based emulsions
such as StoCryl HC 100 or low-viscosity silanes applied in several coatings
with a concentration of active constituents in the order of 100 %, such
as StoCryl HP 200.
Level 3 u Splash zone
In the case of building elements
which are exposed to very high levels
of chlorides, as in the areas of buildings in coastal regions subject to
water cycles or the central supports
of bridges over motorways, the effective penetration depth should be over
6.0 mm. This is referred to as »deep
impregnation«, employing highviscosity, non-water-based systems,
such as StoCryl HG 200.
Modern waterproofing agents are
based on silanes.
The concrete technical specifications and information on the products contained in the Technical Data Sheets and approvals must be observed.
OR
OR
Similar to siloxanes, silicones and
silicone resins, silanes belong to the
chemical group of organosilicone
compounds. After application, these
compounds are transported via
capillary suction into the concrete
surface zone.
OR
Si
OR
R*
Si
Silane
Silane
OR
During the transport process a chemical reaction takes place in the inner
walls of the pores between the silane
and the water absorbed. This gives
rise to a thin, water-repellent film of
silicone resin on the inner walls of the
pores. The transport of water vapour
between the inside of the building
material and the external environment remains possible. The transport
of substances dissolved in water
which are aggressive to concrete is
however prevented.
OH
Si
R*
OH
OR
OR
OR
Silane
Si
Si
OR
OH
HO
HO
R*
O
Si
R*
Si
OH
Si
Si
Si
O
Si
Si
Si
Si
Concrete
The concrete technical specifications and information on the products contained in the Technical Data Sheets and approvals must be observed.
Si
O
Si
OH
O
H2OO H
O
Si
Si
R*
Concrete
O
R*
O
Si
R*
Si
Si
Si
OH
Water splits off from
these silanol molecules,
which
establish
bonds
O
H2O
with the concrete. This
results in a silicone resin
film with a water-repellent
effect on the inner
Si
walls of the pores.
Si
R*
Si
O
R*
OH
O
Si
Concrete
O
Si
R*
R*
Si
R*
Si
Si
O
OH
H2O
OH
R*
O
HO
Si
R*
Si
Si
O
O
Ethanol
R*
Si
Si
R*
Concrete
O
Si
Si
+3 ROH
R*
R*
OH
R*
R*
Ethanol
Silanol
O OH
H2O
Si
Si
Si
Si
OH
OH
The effectiveness and durability of
these measures depend, among other
things, on the chemistry of the
silanes.
As a result of capillary
suction in the concrete
surface zone, a chemical
reaction takes place between the silane and the
water absorbed in the
inner walls of the pores.
In the course of this reaction, ethanol is split off
producing reactive silanol.
+3 ROH
R*
OH
Reaction
with pore water
R*
R*
R*
Si
Si
OH
OH
Silanol
Reaction
with pore water
OH
R*
Silane
HO
Chemical structure of
silanes, which belong to
the versatile organosilicon
compounds, as used in
the deep impregnation of
concrete structures.
OR
OR
OR
R*
Si
O
Si
Si
Aqueous solutions (e. g.
chloride-contaminated
water) on concrete surfaces can no longer be
absorbed by capillary
suction. The minimal
thickness of the film
means that the capillaries
do not become blocked,
however, and the transportation of water vapour
remains possible.
Deep impregnation in detail | 11
Planning and site execution
A method as simple as it is efficient
Swift and straightforward
application of the waterproofing agent.
12 | Planning and site execution
The concrete technical specifications and information on the products contained in the Technical Data Sheets and approvals must be observed.
In the laboratory, core
samples reveal the
carbonation depth of the
construction element.
The high viscosity of the
active agents ensures that
they penetrate slowly
into the concrete.
Attainment of the specified
layer thickness is to be
checked continually during
application.
To ensure the success of “deep
impregnation” as a preventive
protection measure, various steps
need to be observed before,
during and after the waterproofing process.
The effectiveness and durability of the
measure are to a very large extent
dependent on this effective penetration depth. The effective penetration
depth defines the thickness of the
concrete surface zone in which water
absorption is completely prevented.
An advantage when carrying out
on-site monitoring is the use of the
high-viscosity waterproofing agents,
the so-called creams (StoCryl HC 100)
and gels (StoCryl HG 200). These
products remain on the surface for
some time after application. Using a
so-called wet film layer thickness
meter it is possible to ascertain the
applied quantities, check these
against the stipulated requirements
and document the results in the construction diary.
Planning
Cores of at least 70 mm in diameter
are extracted from the building component to be protected. These cores
are then examined at the laboratory
to determine the carbonation depth,
porosity, chloride content and effective penetration depth.
In determining the carbonation
depth, the progressive development
of the carbonation process must be
assessed in order to estimate the
resultant corrosion risk with regard to
the »residual service life«.
The porosity of the building structure
also plays a crucial role in determining
the durability of reinforced concrete
structures. It is also of importance
with regard to the option of deep
impregnation as a surface protection
measure. The capillary porosity of
building structures is established by
dipping and weighing core samples.
The water absorption results serve to
determine the effective penetration
depth of the water-repellent agent as
a reference sample.
The distribution of chloride ions in the
building structure and the chloride
penetration depth are also of significance to the durability of concrete.
Once the chloride front reaches the
reinforcement steel, subsequent surface protection measures will no
longer be effective.
Accomplishment
When all the conditions for deep
impregnation apply, the »effective
penetration depth« and the »minimum active content« are determined.
The results can be stipulated as a
requirement in the invitation to tender and provide the basis for subsequent quality control.
To ensure that the protective measure
remains effective on a sustained
basis, compliance with the stipulated
requirements must be verified at the
construction site. Associated information, including weather conditions
during application and the areas
covered each day, is documented in
the construction diary.
The concrete technical specifications and information on the products contained in the Technical Data Sheets and approvals must be observed.
Quality control
Quality control after the completion
of deep impregnation is carried out in
three steps:
1.Verification that the impregnated
measures have been duly carried
out in the correct manner.
2.Extraction of cores from the
impregnated area.
3. Determination of the effective
penetration depth and the
minimum active content of the
water-repellent agent by means of
FT IR spectroscopy.
Planning and site execution | 13
One step ahead
A forward-looking approach to protection in Sweden
In Sweden, deep impregnation
enjoys an excellent reputation as
a preventive protection measure
and has been in successful use
since the 1990s.
There, the high degree of acceptance
enjoyed by deep impregnation has
resulted in the process being used in
a very large number of building measures.
In order to determine the stability and
durability of deep impregnation, 28
bridge piers were examined in Stockholm on which in-depth waterproofing was carried out to a penetration depth of > 6 mm.
The following selection criteria
applied:
• The building structures were to be
exposed to heavy chloride stress.
• Where possible, the chloride content and carbonation were to have
been determined at the time of
deep impregnation on the selected
structures, so that comparison with
the current tests would reveal the
development of the level of contamination over time and thus
enable the effectiveness of the
measure to be assessed.
• In order to obtain indications as to
the duration of effectiveness, structures were selected which had
undergone in-depth waterproofing
2 to 15 years previously.
Cores were extracted from these
building structures and subsequently
scrutinised at the laboratory. The
examinations revealed that the deep
impregnation had prevented chloride
penetration on all the investigated
bridges and was still fully effective at
the time of testing.
Strömbron, bridge in Stockholm
14 | One step ahead
StoCretec GmbH
Gutenbergstrasse 6
65830 Kriftel
Germany
Head Office
Phone +49 6192 401-0
Fax
+49 6192 401-325
Technical Info Center
Phone +49 6192 401-104
Fax
+49 6192 401-105
[email protected]
Art.-no. 09661-052 rev.-no. 03/08.14 Printed in Germany
www.stocretec.de