Abstract
The purpose of this investigation is to explain fundamental behavior of cylindrical mortar specimens, when they were subjected to dynamic compressive force by a drop-hammer impacting apparatus, and to obtain the comparative test method of dynamic compressive strength of concrete materials. This report consists of three experiments. (Experiment-I) examinated the relations between dynamic stress and dynamic strain of three kinds of mortar specimens when subjected to dynamic compressive force. (Experiment-II) examinated the relation between dynamic energy and dynamic compressive stress under the dynamic compressive force. (Experiment-III) examinated the effect of shape or size of mortar specimens under the dynamic compressive force. Brief of the results of this investigation was as follows. (1) Dynamic compressive stress σ_D of motar specimen is in proportion to a square root of dynamic energy √<U_D> until the mortar specimens were just broken. That is σ_D=α√<U_D> If this relation and the drop-height just when mortar specimens were broken were applied as a factor of strength, dynamic compressive strength of mortar specimens can be presume. (2) Dynamic compressive strength of mortar specimens is 1.8〜2.3 times as static compressive strength. Maximum dynamic strain is 3.0〜4.0×10^-3 as large as maximum static strain independent of impact velocity and weight of a drop-hammer. (3) Dynamic compressive strength of mortar specimen feels the effect of shape or size of specimens as well as static compressive strength. That is, as ratio of the height to the diameter of mortar specimens h/d grow large, dynamic compressive strength becomes smaller. Even if h/d=constant, as the size of mortar specimens grow large, that become smaller.
