超硬練り貧配合コンクリートの圧縮および引張強度に関する実験的考察

Abstract

Prismatic concrete specimens were manufactured by surface vibrating compaction and cube test pieces cut from its upper and lower parts were prepared. The compressive and tensile strengths of the pieces were measured by applying load parallel or perpendicular to the placing direction. Furthermore, compaction mechanism was examined on the basis of the mix analysis test results and the compaction process observed through a transparent side panel of the specimen mould, and the maximum depth of voids contacted with upside and underside of each coarse aggregate was measured.The same tendency was observed on the relation between compaction time and compressive strength regardless of loading direction. At the time of 15 seconds, the strength in the upper part was considerably higher than that in the lower part, because the upper part was changed into relatively dense by sharp subsidence of specimen surface coincided with commecing compaction while the other was in the porous state as yet. Subsequently the strength increased and reached the maximum at the time of 120∼180 seconds. At this stage, air bubbles were dissipated and the voids were filled up by cement paste transfered downward. If compaction was continued moreover, the strength decreased. This resulted from the effect that the transfer direction was turned to upward.The relation between compaction time and tensile strength showed the same tendency as that observed on compressive strength. But, the ratio of cube strength to standard strength was lower than that of compressive strength on the whole, and the tensile strength loaded in parallel to the placing direction was higher than the others in case that crushed stones were used. It was thought that these resulted from the effects of void and bond property between coarse aggregate and mortar.