Abstract
The purpose of this investigation is to examine the effect of coarse aggregate on the fracture process of concrete, by means of the observation of progressive microcracking in concrete specimens. Two kinds of coarse aggregates, Kiso river gravel and artificial lightweight aggregate, were used to examine the effect of material properties of aggregate. The observation of microcracking was carried out by the microphotograph. Brief of the results of this investigation was as follows : 1) Bond crack between coarse aggregate and mortar matrix caused the beginning of structural change of concrete, regardless of the kinds of aggregate and the compressive strength of concrete specimen. 2) For the river gravel concrete, the order of failure process was as follows : (1) beginning of bond crack, (2) appearance of longitudinal tensile crack in mortar matrix, and (3) local compressive failure of mortar matrix at the vicinity of coarse aggregate. 3) The order of failure process of lightweight aggregate concrete varied with the compressive strength of concrete specimen. The order of failure process of low compressive strength concrete was the same to the river gravel concrete, but the order of high compressive strength concrete was as follows : (1) beginning of bond crack, (2) simultaneous appearance and growth of tensile crack in mortar matrix and in coarse aggregate, (3) compressive failure of coarse aggregate and (4) compressive failure of mortar matrix.
