An entire concrete structure can be transformed into an
internationally accepted watertight barrier, with the use of the crystalline
permeability-reducing admixture CHRYSO® CWA 10, from CHRYSO Southern Africa.
Brenton Brouard, technical manager: concrete at CHRYSO
Southern Africa, says that internationally accepted penetration depths are used
to describe the degree of watertightness – or impermeability – of concrete.
The standard stipulates the depth of penetration of water
under pressure, to evaluate the watertightness of concrete to liquid. A 50-mm
penetration depth is classified as being “impermeable with respect to potable
water” and a 30-mm depth as being impermeable with respect to water containing
aggressive substances.
Brouard says this test has been frequently used in South
Africa to evaluate the effectiveness of crystalline permeability-reducing
admixtures. He cautions that these products do not waterproof concrete, but
rather reduce the concrete’s level of permeability and watertightness to
internationally accepted levels; some penetration of liquid under pressure is possible.
Waterproofing of concrete eliminates any penetration of
water into the concrete. This is effected using various 100% waterproof
membranes, which are applied in the form of surface coatings of various
thicknesses.
Whether positive or negative permeability needs to be reduced,
this admixture is ideal for concrete exposed to harsh conditions. By reducing
the permeability of concrete, CHRYSO® CWA 10 protects it against chemicals,
chlorides, sea water and corrosive ground water.
The permeability of a concrete is directly linked to the
continuity of its capillary network. The greater the levels of watertightness effected
in concrete using CHRYSO® CWA 10, the greater the level of discontinuity
induced in the capillary network. This is because its active ingredients react
in the presence of moisture, forming a dendritic crystalline structure
throughout the entire concrete’s pore – or capillary – network. This means less
chance of carbonation, alkali-aggregate reaction or corrosion of the concrete
and its reinforcing steel. Being protected in this way from waterborne soluble
salts, enhances the durability of the concrete and the structure itself.
“Given the right conditions in the presence of moisture, CHRYSO®
CWA 10 can even seal hairline cracks up to 0,4 mm wide.” In the absence of
moisture, CHRYSO® CWA 10 will lie dormant. However, it will reactivate as
soon as it encounters moisture. As long as moisture is present, crystals
continue to grow within the concrete.
The dendritic crystalline formations take place within the existing
crystalline structure of the concrete, so it is an integral system with no risk
of debonding. The reduced permeability – as well as the corresponding
improvement in chemical resistant properties – that can be effected by CHRYSO® CWA
10, will remain even if the concrete surface has been damaged.
Brouard says watertight concrete ( impermeable concrete) is
vital for structures retaining liquid under pressure. “The value of CHRYSO® CWA
10 is that it can reduce the ingress of liquid under pressure to
internationally accepted levels. The concrete becomes a watertight barrier,
with lasting integral permeability-reducing properties.”
“When used as
recommended, CHRYSO® CWA 10 is compatible with all portland cements and their commonly
associated SCMs, as well as most CHRYSO admixtures and a.b.e. products,” says
Brouard. “In addition, it does not adversely affect the slump, strength, air
entrainment or workability of the concrete.”
More information from Elrene Smuts, Tel: +27 11 395
9700 / elrene@chrysosa-abe.co.za /www.za.chryso.com
