Pozzolanas react with lime in Portland cement, resulting in cements that not only require less production energy but also have higher strength and elasticity. Twenty to Thirty per cent fossil meal may be mixed in. In calcined clay/Portland cement, clay is mixed in, in a proportion of 25-40%.
Industrial pozzolanas can also be used. For the production of blast furnace slag/Portland cement; the slag is granulated and ground with Portland cement in a proportion of 1-85%. So-called Trief-cement consists of 60% slag, 30% Portland cement and 2% cooking salt. It is usually recommended to use far less slag - preferably under 15%. Fly ash/Portland cement has about 30% ground in fly ash. The same proportions are used if mixing with industrial silica dust, microsilica. Ground recycled glass is also a potential pozzolana (Pereira etal., 2007). New methods of grinding Portland and pozzolana extra finely together in a vibrating grinder allows the proportion of pozzolana to be increased, for example up to 60% fly ash (Ronin et al., 2004).
Blast furnace slag often slightly increases radioactive radiation from the material. Particles of poisonous beryllium can be emitted from fly ash, and easily soluble sulphates can leach out from waste and pollute the ground water.
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