Properties of Cement and Cementing Materials
Use this handbook as a ready reference to the various types of cementing materials along with their chemical compositions and applications.
TABLE OF CONTENTS Properties of Cement and Cementing Materials
Gypsum Plaster
Gypsum occurs in nature as copper sulphate (CuSO 2.H 2O). Gypsum is a white crystalline salt prepared by precipitating a solution of calcium chloride with dilute sulphuric acid. It is sparingly soluble in water and its solubility increases with increase in temperatures up to 40 C and decreases thereafter. After heating, the monoclinic gypsum is first converted into the orthorhombic form without loss of water. When the temperature reaches 120 C, it loses 75% of its water of crystallization giving the semi hydrate gypsum or plaster of Paris. When heated to about 200 C, it loses all its water of crystallization. It does not recombine with water after this stage and is said to be dead burnt. Above 400 C, it decomposes into calcium oxide.
Plaster of Paris
Plaster of Paris is obtained by heating gypsum at 120 C in a kiln. If it is heated to more than 130 C, the setting properties of plaster of Paris are partly destroyed. Plaster of Paris is a white powder, which vigorously combines with water to form a plastic mass, with the release of heat. It quickly sets to a hard porous mass. This change occurs in two steps. The first step is called the setting step while the second step is called the hardening step. The final product is obtained after setting is plaster of Paris. While setting, a slight expansion of 1% in volume occurs so that it fills the mold completely and takes a sharp impression.
Uses
Plaster of Paris is...
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