抄録
In building works, the premature cracks of concrete are often observed soon after the concrete has been placed. The cause of crack occurrence of this nature, however, has not yet exactly known. The author has been studying the field data on extraordinary phenomena during concrete setting, including the false set. In the course of study, the author has noticed that some of factors underlying the phenomena of premature cracks may be same as those for the extraordinary sets of concrete, that is, contrary to the wide-spread concept that the cause of premature crack has the direct relation to the fineness of cement or the rapid desiccation, this phenomenon is caused by the slight tendency of the cement itself to make false setting. In the present paper the correlation between above two phenomena is discussed based on field data and, then, experimental results are presented on the nature of initial setting and the initial rate of shrinkage of the cements.
