A Study on Strength of Gypsum

Abstract

Ii freshly mixed plaster is allowed to set, a part of water, which is it excess of the theoretical amount requuired to bring about the chemical change, evaporates.The set mass attains the maximum strengtn, when the mixed plster has dried completely. It is inevitable that the set mass becomes incompact to some extent. The maximum hardness and strength attained after setting, however, depends mainly upon the compactness of the set mass and, therefore, varies inversely with the proportion of water used.If compressed, the cracked set mass slips along the slip plan. If more water is used in maxing, the set mass will be more incompact and slips easily. Therfore, its strength is abated.I tried to set forth this relation of stregth and compactness of strength and compactness of gypsum in formulae. In woaking out the formulae, it was assumed that the set mass is homogeneous, has no air bubbles in it and that the volume does not change in the process of setting.The theoretical formulae are given as follows:logσx1/σx0=n logρ1/ρ0 or logσx1=n logρ1-logσx0/ρ0nWhere σx1 &ρ1: compressive strength and apparent specific gravity of set massn: experimental constantσx0 & ρ0: compressive strength and apparent specific gravity of the ideal set mass for which only the theoretical amount of water required to bring about the chemical change is used.apparent gravity=weight of specimen/volume of specimenSpecimen were tested after seven days. The theoretical formulae indicate a straight line. The logρ1-logσx1 curves obtained from the experiments endorsed this anticipation.It is concluded that n is affected by conditions of crystallization of plaster. Therefore, qualities of plaster is detrmined by the value of this constant.