Clinker is anhydrous (without water) having come from a hot kiln. Cement powder is also anhydrous if we ignore the small amount of water in any gypsum added at the clinker grinding stage. The reaction with water is termed "hydration". This involves many different reactions, often occurring at the same time.

Waterproof cement is the name given to a portland cement to which a waterrepellent agent has been added. Hydrophobic cement is obtained by grinding portland cement clinker with a filmforming substance such as oleic acid in order to reduce the rate of deterioration when the cement is stored under unfavourable conditions.

The clinker is next ground to cement (perhaps after a drying stage). Here calcium sulfate is added to control set, in the form of a highpurity grade of gypsum or anhydrite . In some specifiions (not ASTM ), a small amount of titanium dioxide may be added to improve reflectance.

Another essential raw material is gypsum, some 5 percent of which is added to the burned cement clinker during grinding to control the setting time of the cement. Portland cement also can be made in a combined process with sulfuric acid using calcium sulfate or anhydrite in place of calcium carbonate.

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Jun 01, 2017 · CEM I of strength class was used in this research. The percentage of clinker and gypsum in the cement was 95– and 0–5% respectively, while the specific gravity and fineness of OPC was found to be and % (#200 sieve) according to ASTM C187 and ASTM C786 (ASTM, 2016d), respectively.