Waterproof cements are used for water retaining structures such as tanks, reservoirs and swimming pools. The composition of the cement is such that it will not be affected by the presence of water.
Waterproof cement is produced by grinding Portland cement clinker with a film-forming substance such as sodium silicate, aluminium stearate or sugar, and a little gypsum. Grinding is done to obtain a uniform and intimate mixture of the film-forming substance throughout the mass of cement. The proportion of film forming substance added to the cement varies with manufacturers and ranges between 2% to 6%. This addition also makes waterproof cement more expensive than ordinary Portland cement.
Waterproof Cement – Precast Concrete Products: a guide on the use of waterproof cement
Waterproof cement is a precast concrete and masonry construction product that is used to prevent the passage of water through hydraulic structures and in the construction of water retaining structures.
It is applied to surfaces subject to hydrostatic pressure or to surfaces in contact with earth which is saturated with water or which may be covered by water when subjected to hydrostatic pressure as in the case of submerged foundations, retaining walls and swimming pools.
Waterproofing cement should also be used for bedding pipes carrying sewage and surface water, for forming channels and gullies in floors and laying manholes.
The use of waterproof cement may be necessary in circumstances where the structure to be concreted is likely to be subject to dampness, e.g. the construction of water retaining structures and basement floors.
It should be used with care because:
Where it is used in structural concrete, the water content must not exceed that required to obtain maximum density and this will generally be less than that used in conventional concrete.
The reduced water content gives a stiffer mix which may make placing more difficult.
Waterproof cement should not generally be used for mixing with aggregates when making mortar for pointing or rendering as one of its functions is to reduce the water penetration into porous masonry units such as brick and concrete block.
It is a commonly held misconception that waterproof cement can be used for cast-in-situ ground slabs, but there are no exceptions made in BS 8110 for waterproof cement.
Waterproof Concrete and Waterproof Cement.
The terms waterproof concrete and waterproof cement are misnomers as cement by itself is not waterproof. A concrete mix could be described as waterproof if it is impervious to the ingress of water.
Waterproofing can be achieved by using admixtures, or by using membranes or coatings.
In the case of admixtures, a super plasticizer or high range water reducer which has the ability to reduce the water content in a concrete mix without reducing workability, will produce a denser concrete than normal Portland cement alone. This type of admixture is also referred to as an air entrainment admixture and can be added during batching of the concrete.
In some cases, admixtures are used during batching to increase the density of concrete so that it becomes impermeable to water. In other cases, special aggregates are used in place of normal aggregates when producing concrete. Such aggregates are usually made up of very fine materials such as fly ash (a fine powder produced by burning pulverized coal in an electric power generation plant). The finer the particles are, the denser the resulting concrete will be.
The use of membranes or coatings to provide protection for precast products
Waterproof cement is used in the construction of water retaining structures such as tanks, reservoir, swimming pools and other structures where contact with water is inevitable. The use of waterproof cement is also recommended where the structure will be subjected to wetting and drying cycle. In this article, I shall focus on the type of cement that can be used for waterproofing both walls and slabs in concrete structures.
The main reason why we need a waterproof cement is because it helps to reduce the permeability of concrete structures. The use of a waterproofing agent such as acrylic latex helps to improve the quality of water-cement ratio (w/c) by reducing the surface tension of water which in turn reduces its ability to penetrate cracks. In addition to this, it has been observed that concrete with a low w/c ratio has higher compressive strength than those with high w/c ratio. Thus, using a waterproofing agent helps to improve the compressive strength of concrete.
Waterproof Cement is used for water retaining structures.
The cement and aggregates used in the manufacture of Waterproof Cement should be selected and proportioned so that the resulting concrete is suitable for its intended use. The quality of cement and aggregates should be checked as per relevant Indian Standard Specifications.
The more important properties are explained in this chapter.
Waterproof cement, often referred to as water resistant cement is a product that resists water ingress into the cement matrix and structure. There are two types of waterproof cement, Hydrophobic Cement and Crystalline waterproofing.
A hydrophobic cement is a cement which produces a mortar or concrete that is relatively impermeable to water. The first type of hydrophobic cement was developed by the Le Chatelier process in France. In this process large amounts of finely ground limestone were added to the clinker together with a small amount of gypsum. This required the use of high temperature rotary kilns which used more energy than ordinary Portland Cement (OPC). The process was later modified by using fine slag instead of limestone which reduced the energy consumption but still produced a weaker cement.
In the 1950’s Grasselli Chemicals patented what they called “Water Repellent Portland Cement”. This cement was produced by grinding OPC clinker with an oil to produce a finer grained and more reactive product which set more rapidly and had higher early strengths than OPC. This type of hydrophobic cement is now manufactured by many companies around the world but each manufacturer has