Corrosion society preprufe article

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:

[email protected].