This paper presents the results of laboratory studies on the influences of concrete admixtures to the compressive strength, drying shrinkage and cracking tendency of concretes. Four agents were tested, two of which were air entraining agents and the rest were cement dispersing agents with set retarding effect. Test results show that these agents reduce the water requirement remarkably, although the reduced water content does not necessarily accompany improved properties of concrete. Water requirement was observed to be affected by the type of admixture as well as that of coarse aggregate. Both of two cement dispersing agents increased compressive strength and drying shrinkage but the prominent difference was observed between the effects of them. No significant influence was found to the cracking tendency of concrete by these admixtures. One of the air entraining agents decreased compressive strength of concrete considerably, while the strength of concrete with the other was almost equivalent to that of concrete without any admixture, Both of the two air entraining agents increased drying shrinkage and accelerated cracking tendency, the cause of which was considered attributable to the entrained air.
　These test results are considered to suggest the great significance of tests on concrete admixture before employment.