Chryso for watertight concrete with crack-healing properties
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
