International Concrete Abstracts Portal

This paper presents the results of an investigation to determine the performance characteristics of concrete made with recycled coarse aggregate from a plant. Slump and air content of fresh recycled aggregate concrete are studied. The compressive strength, drying shrinkage and resistance to freezing and thawing were investigated experimentally when the types and combinations of coarse aggregate, admixture, air content and so on were varied. It was found that the recycled aggregate concrete decreased the compressive strength at 7 to 28 days as compared with those properties of the control concrete. The decrease in strength can be suppressed low by partial use of recycled coarse aggregate. Drying shrinkage of recycled aggregate concrete showed larger value than conventional crushed aggregate concrete. The use of shrinkage reducing agent can reduce the drying shrinkage of recycled aggregate concrete. The resistance to freezing and thawing of recycled aggregate concrete was lower than that of control concrete of similar composition. The decrease in resistance to freezing and thawing can be suppressed low by partial use of recycled aggregate, reducing W/C and increasing entraining air.

The void diameter and the internal surface area of porous concrete (PoC), prepared with crushed stone and glass balls of differing diameters as aggregate, were determined by slicing off the central cross section, cutting it into pieces at constant intervals and making an image analysis of those sections to examine the effect of the analytical results on the physical properties of the porous concrete and the growth of plants. The results indicated that the mean void diameter of the porous concrete is approximately 0.22 to 0.24 times the particle diameter of the aggregate packed with 30% binder and that the interconnected void, approximately 3 mm in mean diameter, is appropriate for grass-planting concrete.

Green Concrete is a concrete on which plants such as grasses and bushes directly grow up. It is expected to utilize for increasing the amount of the green around buildings and civil structures. It consists of no-fines concrete, water retentive material in the void and thin soil layer sprayed on the surface. The no-fines concrete is made of single sized crushed stone and low alkaline cement paste. Chopped peat moss which retain water and fertilizer is filled in the void. Seeds mixed with the soil germinate, take roots into the void and grow up. In this paper the results on the relation between the strength and the void ratio of concrete, and the effects of cement types on the alkalinity leached from hardened cement are presented. Plants growing performance of the Green Concrete is also presented based on planting tests by using lawns and actual application. The optimum void ratio of concrete was approximately 2530% when the compressive strength was approximately 10-15 N/mm’. In this condition of concrete it is demonstrated that herbaceous plants and some kind of trees sufficiently grow on the Green Concrete.

It is anticipated that coal-tired thermal power stations will increase in Japan and that the discharged amount of coal ashes, which are industrial by-products, will rapidly increase in the future. In order to effectively use the bottom ash discharged from coal-fired thermal power stations, concrete which substitutes bottom ash from 0 to 40 percent in volume for fine aggregate was investigated in this study. The compressive strength, tensile strength, freezing and thawing resistance, and abrasion resistance of the concrete were examined. The results of the concrete strength tests indicate that the compressive strength and tensile strength of bottom ash concrete generally increases with the increase of replacement ratio of fine aggregate and curing age. The freezing and thawing resistance of concrete using bottom ash is lower than that of ordinary concrete and the abrasion resistance of bottom ash concrete is higher than that of ordinary concrete. The use of bottom ash in amounts of 10 to 40 percent as replacement for fine aggregate is effective in improving the concrete properties except for the freezing and thawing resistance.

new method of producing high-strength porous concrete has recently been developed in Japan. In this method, porous concrete is produced by coating the coarse aggregates with a high-strength mortar, then applying vibration to fuse them. Porous concrete produced bythis method has the following properties. It has a continuous void system with a volumeko-total-void ratio exceeding 85% and a compressive strength of 20 MPa or greater when water permeability is 2 crnkc. The porous concrete produced exhibited good durability in freezing and thawing tests (ASTM C666, Procedure B) and while the amount of drying shrinkage is about 60%, or smaller than that of conventional concrete, such shrinkage occuring very rapidly.