Water-repellent admixtures

These causes may be superimposed, and other causes may be involved as well. The following counter-measures are available changing to raw materials of different composition (in particular, a low alkali content) and using water-repellent admixtures in the clinker grinding mill, so that the cement is rendered "hydrophobic" and thus insensitive to moisture. 

Admixtures are sometimes used to reduce permeabiUty of concrete (80—82). These iaclude pore-filling materials such as chalk. Fuller s earth, or talc water repellents such as mineral oil, asphalt, or wax emulsions organic polymers (acryflc latexes, epoxies) and salts of fatty acids, especially stearates. 

Concrete dampproofers are integral admixtures that alter the concrete surface so that it becomes water repellent, or less wettable . This is illustrated in Fig. 4.1, which shows a close up of a water drop on a surface of a concrete that has had a dampproofer incorporated into it. This water repellency conferred on the concrete is only effective in preventing water from entering the surface when the applied pressure is small, e.g. rainfall in windy conditions, or capillary rise. The latter effect is shown in Fig. 4.2. In view of this, these materials are used normally for improving the quality of concrete pavers, tiles, bricks, blocks and cladding panels where the additional benefits of reduced efflorescence, the maintenance of clean surfaces and the more even drying out of adjacent bricks and panels are also obtained. 

Dampproofing admixtures are water-repelling materials such as wax emulsions, soaps and fatty acids which react with cement hydrates [84, 85]. The most widely used water-repelling materials are the calcium or ammonium salts of fatty acids such as stearates. Proprietary products are available both as dry powders and liquids. Usually, a stearate soap is blended with talc or fine silica sand and used at the prescribed dosage per weight or bag of cement. In commercial liquid preparations, the fatty-acid salt (soap) content is usually 20% or less, the balance of the solid material is made up of lime or CaCl2. Some proprietary admixtures combine two or more admixtures, e. 

Damp-proofing admixtures or water repellents can also be added to concrete. However, several researchers indicate that they offer little benefit to corrosion protection in good quality concrete [52,53]. Succinate type admixtures have been tested at the Universities of Connecticut and Massachusetts [54,55]. Good dampproofing and corrosion resistance properties were shown however, due to the extreme drying conditions and artificial cracks, it is not known if these materials raise the chloride threshold level at the reinforcing steel for corrosion initiation. 

These admixtures decrease water penetration across a hardened porous cement matrix, bnt cannot be used to eliminate water migration and the term damp-proofing is not correctly applied. They are used on concrete surfaces against rain and gronnd water penetration. The water repellents are produced on the basis of silicones, acrylic resins or petroleum products. 

They are applied on roofs, slabs on ground, basements, water-retaining structures, concrete blocks, and clay bricks. Waterproofing admixtures reduce the permeability of concrete. The dampproofing admixtures impart water repellency and reduce moisture migration by a capillary action. Examples of these admixtures are soaps and fatty acids which react with cement, conventional water reducers, methyl siliconates, etc. 

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