Control of cracking caused by autogenous shrinkage in mass concrete

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Influences of cement type, mix proportion, temperature and specimen size on autogenous shrinkage of concrete were investigated. Influence of autogenous shrinkage on cracking of mass concrete was also investigated with restraining tests where temperature and stress histories of specimens were controlled. Main results of this research are as follows.(1) Influence of cement type on autogenous shrinkage can be setimated with mineral compositon and degree of hydration. Autogenous shrinkage increases by using blast furnace slag with 6000-8000 cm^2/g Blaine Fineness.(2) Predicting model for autogenous shrinkage strain of concrete was proposed. It is function of cement and admixture type, water-binder ratio and effective age. The proposed model is effective for concretes with ordinary Portland cement and with water-binder ratio between 0.2 and 0.56.(3) The rate of autogenous shrinkage increases with temperature of concrete within the range from 20 to 60 ﾟC.It is proved that this effect can be estimated with maturity concept. Autogenous shrinkage during the first 24 hours is lager for a specimen with lager dimensions.(4) Contribution of autogenous shrinkage to restrained stress is increased with decrease in water-cement ratio. For silica fume concrete with water-cement ratio of 0.20, tensile stress generates even when temperature is still increasing. This is because autogenous shrinkage overcomes expansion due to temperature rise.