Dampproofing admixtures

In water-retaining structures or basement concrete subject to high hydrostatic pressure, materials of this type are generally not beneficial. However, some dampproofing admixtures do contain water-reducing admixtures and will result in a reduction in permeability under an applied hydrostatic head. In addition, the reduced capillary size and quantity will increase the hydrostatic pressure required to enter the concrete surface (see later). 

This type of dampproofing admixture is widely used in the concrete products industry, in particular the calcium and aluminium stearates. The calcium stearates can be produced by grinding stearic acid with lime or cement to produce a material containing 10-30% calcium stearate. 

There is not a great deal of published data on the effect that dampproofing admixtures have on cement pastes in the way that water-reducing and air entraining agents have been studied, but some observations can be made. 

It is believed that in the presence of dampproofing admixtures, the surfaces of the concrete, and the internal surfaces of the pores become coated with either a layer of molecules in the case of stearic acid and other fatty acids (Fig. 4.5b) or a layer of coalesced or separate particles of material in the case of waxes and bitumens, etc. (Fig. 4.5c). The end result in both cases is the production of hydrophobic surfaces exhibiting high contact angles to water, as shown in Fig. 4.6. 

Fig. 4.5 The molecules or particles of the dampproofing admixture line the capillaries with a hydrophobic sheath.

Dampproofing admixtures are formulated to affect the properties of the hardened concrete, and not those of concrete in its plastic state. In the case of materials based solely on calcium and aluminum stearates, stearic acid in solid or emulsion form, bitumens and hydrocarbon resins, there will be no effect on the properties of the plastic concrete with regard to air content, workability, mix design parameters, etc. When water-reducing admixtures or accelerators are included in the formulation, the effect on the concrete will be a function of the particular type of material used (see relevant section). The wax emulsions do appear to have an effect on the properties of the plastic concrete because of the lubrication effect of the very small... 

The presence of the dampproofing admixture at higher levels completely inhibits disfiguring algal growth. 

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. 

The dampproofing admixtures will, therefore, improve the aesthetic qualities of concrete in terms of maintenance of a clean appearance over a prolonged period of time without adverse effects on other properties, and in the areas of freeze-thaw resistance, shrinkage under wet-dry cycling and reinforcement protection, may contribute beneficially. 

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. 

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. 

Fig. 4.7The freeze-thaw resistance of plain concrete and concrete dampproofed with a wax emsulsion type of admixture. 

Uses Cement admixture elastomeric textile thread adhesives (cold-sealable pkg., selfsealing envelopes, leather/tile adhesives, pressure-sensitive) binder for tufted carpet anchor coatings, flock attachment, nonwoven fabrics carpet foam backings dampproofing formulations latex dipping compds. (gloves, contraceptives, balloons) molded latex foam natural rubber castings rubberized hair prods. in food-pkg. adhesives and pressure-sensitive adhesives... 

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. 

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