Abstract
This paper is to follow the previous part 1 and 2, in which basic properties and responses to several conditions of the environment of Gypsum are studied. In this paper experimental results and some considerations on mechanical properties of cast Gypsum are explained and concluded as follows. The compressive strength of cast Gypsum which is made in the season when the monthly average temperature is lower than 18℃ or with the temperature arrangement, is possible to be attained constantly over 150kg/(cm)^2 under wet condition and over 300kg/cm^2 under dry condition. The young's modulus of cast Gypsum is around (10)^5kg/cm^2, almost half value of Cement Concrete, and decreases by absorbing water as in the case of the compressive strength. Cast Gypsum has very small bond strength between smooth surfaces like the round steel, but the bond strength over 10 percent of the compressive strength can be obtained by using deformed bars. The creep of cast Gypsum is prospected larger than Normal Portland Cement. By short time experiments the creep rate of cast Gypsum under dry condition becomes begger than 1 after 1 month loaded with 33 percent stress of the compressive strength. The tensile strength of cast Gypsum is from 3 to 10 percent of the compressive strength. It is sure that Gypsum is inferior to Cement Concrete in many mechanical properties mensioned above, but there are cirtain posibilities to use cast Gypsum as structural materials in buildings.
