Yoshitake OGUCHI

Study on Shrinkage of Concrete Considering Properties of Aggregate

Takumi SHIMOMURA

Recently, it is reported that some kind of concrete shrinks so much beyond expectation. Shrinkage of aggregate is come up for one of possible causes. However, the shrinkage of concrete is mainly originated by the shrinkage of cement. Therefore, the role of aggregate in shrinkage of concrete is reconfirmed in this research.
First of all, effect of elastic modulus of aggregate is examined in autogenous shrinkage and drying shrinkage. Several artificial materials which are nonhygroscopic are used as coarse aggregate. These tests results clarified that "series mechanism" which expresses diluting effect by the existence of aggregate is dominant in drying shrinkage, while the contribution of "parallel mechanism" which expresses restraint effect of aggregate is not significant.In prior to drying shrinkage test of concrete specimen with natural rocks, the drying shrinkage of various rocks are measured. Then, typical rocks are selected from among that. Concrete specimens are made with these rocks and drying shrinkage is measured.
It is reconfirmed that there was no need to consider the shrinkage of aggregate to estimate the shrinkage of concrete when the shrinkage of aggregate is relaDrying shrinkage of concrete specimen is estimated with "complex model". Complex model is valid in many cases. But the model overestimates the shrinkage of concrete with some kinds of aggregates such as lime stone and chart. This result implies the existence of as-yet-unknown preventive mechanism against drying shrinkage.

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