Shigemitsu Hatanaka

Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

Abstract To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0–135.0 MPa and 5 void ratios between 15%–35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm (Nos. 7, 6 and 5 according to JIS A 5001) were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.

STUDY ON IMPROVEMENT OF SMALL-DIAMETER DRILLING TESTER AND IT’S APPLICATION EXAMINATION FOR CONCRETE

A small-diameter drilling tester developed by the authors is one of the slight-destructive testers, with which the damage of materials tested can be very small. To apply the tester for checking the strength of compound materials e.g. Portland cement mortars, concretes etc., a series of experiments was carried out 1) to avoid the ill effect of cement powder discharged around a drill, 2) to avoid drilling coarse aggregates, and 3) to know the best magnitude of pressure for drilling. As a result, it is clarified that the testing method may be improved by considering the obtained data.

EXPERIMENTAL STUDY ON IMPROVEMENT OF SURFACE MICRO CRACK OF VACUUM PROCESSED CONCRETE SLAB

Very fine plastic shrinkage crack is often reported to occur on vacuum processed concrete slab, which is considered due to cement-richness of a surface layer. A shrinkage-reduction admixture is used in order to prevent such plastic shrinkage cracks. Although the cracks can be avoided by this method, white powders of CaCO3 sometimes appear on the surface. The effects of the admixture and curing condition were investigated on the amount of powders and the bond strength. It was found that appropriate addition of the admixture successfully reduces the plastic shrinkage cracks without producing powders on the surface.