This cement is produced by grinding together a mixture of 80 to 60 percent of Portland cement and 20 to 40 percent of Pozzuolana . Pozzuolana may be a natural active material , such as volcanic ash or pumice or an artificial product such as burnt clay or shale containing silicious and aluminous mineral substances . The rate of development of strength is lower than that of normal Portland cement , especially at low temperatures .
Pozzuolana in optimum proportions with cement (20 to 30 percent of Pozzuolana ) improves the quality of concrete . it increases the workability , lowers heat of hydration and increases the water tightness . This cement has got greater resistance against sulphatic action and sea waters. Moreover it decreases the cost and is usefu; in the mass concreting works .
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