Abstract
The authors have studied on the gypsum admixing ratio to cement so as to prevent the shrinkage crack of concrete due to dring. The optimum gupsum admixing radio to cement is 3% by weight, in regardless of the types of cement or gypsum, and the kind of gypsum which showed the best, was gypsum anhydride gained by calcination of the residuum gypsum. On account of the properties more improvement, we prepared the special type cement admixed 5-15 °/wt ground lime stone to the above mentioned cement (SO_s 3°/wt), and tried to use at two building sites. The test concrete used this cement, in comporison with plain concrete, brought about good results of very few cracks. The theoretical expression for cracks creation formulized from measuring values and calculated factors, adapted to a degree with practice. This formura is showed as follow : S/a-(1+k)/E=f here, S=Coefficient of contraction E : Young's modulus k : creep a : Constant, defines by section f=Restrain factor of a building
