Corrosion society preprufe article
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14 MATERIALS PERFORMANCE December 2012 NACE International, Vol. 51, No. 12
Material Matters
Adhesive waterproof membrane protects reinforced concrete from water ingress
the concrete’s porous surface.
Structures built on the sea-
front or on nearby reclaimed
land are exposed to high levels
of sulfates and chlorides
through saline groundwater
conditions and aggressive at-
mospheric conditions. Corro-
sion of reinforcing steel oc-
curs when chloride ions from
seawater or airborne salts
diffuse into the concrete build-
ing foundations and base-
ments through cracks and
pores and reach the steel. The
chloride ions accumulate to
the level where the steel’s pro-
tective Ålm is compromised
and it begins to corrode. The
additional volume of corro-
sion products on the steel ex-
erts tensile stress on the con-
crete, causing it to crack
further and create more paths
that allow the ingress of con-
taminants. The aggressive
nature of coastal groundwater
can negatively impact the du-
rability of structural concrete
and, consequently, the dura-
bility of the overall structure.
The adhesive waterproof membrane was
used to protect the substructure of
Vodafone Village, a €300 million
high-rise office building complex in
Milan, Italy. Photo courtesy of Grace
Construction Products. Concrete is a durable
and robust compos-
ite material used to
build a variety of
structures. Its in-
herent nature—a fluid mix-
ture of aggregate, cement, and
water that hardens into a
permeable solid—makes it
susceptible to cracking due to
shrinkage as it sets and ma-
tures, as well as vulnerable to
groundwater and atmospheric
contaminants that penetrate
NACE International, Vol. 51, No. 12 December 2012 MATERIALS PERFORMANCE 15
Information on corrosion control and prevention
External waterprooÅng membranes are
widely used to prevent water from penetrat-
ing below-grade steel-reinforced concrete
slab structures and protect them from the
ingress of chlorides and sulfates from
groundwater or moisture in the soil. During
construction, the membrane is Åtted against
the forms and the concrete is cast against
it, explains NACE International member
John P. BroomÅeld, FNACE, consulting
engineer with Broomfield Consultants
(Surrey, United Kingdom) and a NACE-
certiÅed Corrosion Specialist.
“The membrane must seal against all
piles supporting the basement. In a large
building there can be hundreds of piles. Site
practice does not lead to precision engineer-
ing and leaks are common,” BroomÅeld
explains. “Also, any minor tears or defects
in the membrane will allow water behind it
where it can then ‘look’ for cracks or con-
struction joints. This often results in a sig-
niÅcant hydrostatic head of water behind
the leaks in the deep basements,” he adds.
Once a membrane is breached, the
whole concrete foundation is vulnerable to
the presence of migrating groundwater,
which can also lead to corrosion of the re-
inforcing steel if chlorides are present in the
groundwater. When a leak becomes visible,
it is often a considerable distance from the
actual source, which makes leak detection
challenging and remediation expensive.
The concrete may have been exposed to
chloride-contaminated groundwater for
some time before the leak is detected and
repaired. The presence of groundwater in
a basement structure also can be damaging
to the building’s plant components as well
as its fabric, which compromises the build-
ing’s full use.
To address the issue of water leaking
and migrating between a waterproof
membrane and the concrete structure it’s
Continued on page 16
16 MATERIALS PERFORMANCE December 2012 NACE International, Vol. 51, No. 12
M A T E R I A L M A T T E R SM A T E R I A L M A T T E R S
installed to protect, Grace Construction
Products (Berkshire, United Kingdom)
developed a composite membrane with a
synthetic adhesive that permanently
bonds with poured concrete. The 1.2-
mm thick membrane is a composite sheet
that consists of three layers: a 0.8-mm
thick high-density polyethylene (HDPE)
backing; a malleable, pressure-sensitive
adhesive layer; and a weather-resistant,
microporous top layer that provides a
surface suitable for foot trafÅc.
Designed for use when constructing
structures such as basements, foundations,
underground parking garages, tunnels,
and underpasses, the waterproof compos-
ite membrane is laid on top of the concrete
blinding or mud slab layer, with the
HDPE side facing down, before the struc-
ture’s concrete foundation is poured. The
membrane, provided in 1.2-m wide rolls,
has one self-adhesive selvedge that enables
one strip of the membrane to be fully
sealed to the next strip when overlapped
Continued from page 15
so the continuous bond to the concrete is
maintained. Before the concrete is poured,
any tears seen in the membrane can be
repaired using an adhesive tape that in-
corporates the same composite layers that
comprise the membrane.
Steel reinforcement is then installed
on top of the membrane’s surface layer.
According to Kevin O’Gorman, Grace
Construction Products’ global projects
leader for European Middle East, Africa,
and India, as the structural concrete is
poured directly onto the membrane, it
passes through the microporous surface
layer to reach the underlying adhesive
layer. As the concrete hardens, mechan-
ical and adhesive forces combine at the
concrete/membrane interface to create
a permanent, continuous bond and seal
that prevents water migration and re-
duces risks of leaks. The bond enables the
membrane to remain sealed to the con-
crete even if the ground settles.
The bonded HDPE membrane pro-
vides an isolation layer between the build-
ing’s foundation or basement and the sur-
rounding grounds and groundwater, and
acts as a physical barrier against most
chemicals, including sulfates and chlorides.
If there is a puncture or other damage that
allows water to get through the HDPE
membrane, the bond between the concrete
and the adhesive layer prohibits the water
from tracking above the membrane and
Ånding a way into the concrete, explains
O’Gorman. He notes that a loose mem-
brane, which is not bonded to the structural
concrete, can allow water to migrate be-
tween the membrane and structural con-
crete if it is punctured, and penetrate into
cracks and defects in all areas of the struc-
tural concrete. By eliminating water migra-
tion, the membrane mitigates corrosion of
the reinforcing steel and enhances the
structure’s long-term structural perfor-
mance and durability.
Contact Grace Construction Products—e-mail: