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Fosroc manufactures a variety of admixtures, used in almost all major projects.
Waterproof concrete is often confused with water-repellent concrete. However, the two are quite different in design and function.
Water repellency can be defined as resistance to surface water that is not under pressure and this can be achieved by reducing the capillary attraction within concrete. Waterproof concrete can be defined as "concrete that prevents the ingress of water that is under a significant pressure, typically arising from static head in water storage vessels''.
Water repellency is useful for the reduction of surface staining or discoloration and is often applied to decorative or ornamental concrete where the aesthetic appearance is of significant appearance. It can be achieved by coating the pores with a hydrophobic material such as a stearate or a silane-based chemical. Many solutions for achieving water repellency involve the surface applications of clear coatings containing silane solutions or silicones.
Waterproof concrete is a much more challenging proposition and the degree of "waterproofness" required is very important. To achieve a good waterproof concrete, it is essential to consider both the design of the concrete and the workmanship associated with its placement and after-care. The best design is quite useless without adequate workmanship.
Design parameters
BS 8110:1985 and specifically BS 8007:1987 address the issues associated with design and good practice. The most recent of these specifications is now 15 years old and concrete technology has moved on considerably since they were compiled. BS 8007 speaks about a minimum cement content of 325 kg/cu m and a maximum water/cement ratio of 0.5 but largely ignores the use of admixtures with the exception of a general reference in BS 8110 clause 6.1.5.
It is possible to make waterproof concrete without admixtures but it is much easier to achieve the desired results reliably with the inclusion of admixtures to reduce the water/cement ratio and thereby reduce permeability.
The constituents of a good waterproof concrete are as follows:
Superplasticisers such as melamines, napthalenes and poly carboxylates can be used to reduce the water demand by 20 per cent-plus and can render the resultant concrete even more impervious and act as very efficient waterproofers indeed. There are hybrid admixtures that act as both pore blockers and water reducers but the efficiency of such a dual approach is beyond the scope of this brief article.
Cautionary note
The temptation to use admixtures to overdesign the concrete performance should be resisted as other problems may arise. Too much cement equates to an increased shrinkage potential and cracked concrete is not waterproof.
With some of the powerful superplasticisers, it is possible to reduce the water so much that any significant failing in the curing regime may lead to desiccation and localised drying shrinkage.
Workmanship
The best concrete mix design is never enough - workmanship associated with construction of leakproof formwork, good access to the concrete formwork, accurate and efficient vibration and conscientious curing all add dramatically to the waterproof integrity of the structure as cast.
In summary, the concrete function should be defined clearly and either water repellency or waterproof construction design specified. Confusion of the definition can result in some very unfortunate failures. Fosroc can offer assistance in the design of waterproof concrete.
