Materials which react with cement hydration products

Materials which react with cement hydration products... 

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. 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

The thermal decomposition of limestone - which was reported by Cato in 184 bc -at about 900 °C produces calcium oxide (lime, technically called quicklime ) (CaCOj CO2 + CaO). This is an important basic step in glass and ceramics production, and quicklime in combination with clay is also a cheap essential raw material for the cement industry. For the estimated worldwide production of cement in 1994, the consumption of limestone was about 1420x10 (metric) tons. Quicklime reacts with water to calcium hydroxide Ca(OH)2. Hydrated lime is a dry calcium hydroxide powder, while slaked lime is an aqueous suspension of calcium hydroxide particles in water. Both forms are the cheapest industrial alkaline chemical and are frequently used together with limestone as a neutralizer for acids, for example in flue gas desulfurization (see below) (Oates 1998). The annual global production of lime and lime compounds is estimated to exceed 300x10 tons, with highest amounts in China, followed by the USA, the former Soviet Union, Germany, Japan, Mexico and Brazil (Oates 2002). 

Metakaolin reacts with lime to yield calcium silicate hydrate. Metakaolin may also be activated by other materials such as alkali metal hydroxides, water glass, etc. Activation leads to a polycondensation product with cementing properties. The t5q)e of MK, composition, temperature at which it is produced, surface area, etc., determine the strength development characteristics of the product. In conduction calorimetry, an exothermic peak results by the reaction of MK and the activator. A strong as5mimetric peak in calorimetry is associated with an amorphous inorganic... 

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