RESEARCH ON THE CHARACTERISTIC OF CONCRETE WITH RECYCLED AGGREGATES IN NUCLEAR POWER PLANTS (PART1): EFFECT OF THE CHARACTERISTIC OF HIGH-QUALITY RECYCLED AGGREGATE ON UNIT WATER CONTENT AND COMPRESSIVE STRENGTH

Recycled aggregates are classified into four types of quality (JIS A 5023, JIS A 5022, JIS A 5021, JASS 5N). Although there were many reports and studies on recycled aggregate and concrete, few reports focused on adhered mortar which were contained in high-quality recycled aggregate. In the previous paper we reported that the adhered mortar ratio of the recycled aggregate and mortar particle amount had a high correlation with the water absorption and the absolute dry density, and most of the mortar content was the weight of mortar particles. We are studying the properties of concrete using high-quality recycled aggregate from demolished concrete. This paper presents the effect of mortar particle amount on the unit water content, compressive strength, and the Young’s Modulus of concrete. (1) Regardless of the method for producing high-quality coarse aggregate, the larger the amount of mortar particle in recycled aggregate, the lower the unit water content of fresh concrete with the same slump. There is a negative correlation between the amount of mortar particles and the unit water content. Since the resistance between coarse aggregates was reduced by the rounded mortar particle and the shape of original gravel.(2) Regardless of the method of producing high-quality coarse aggregate, the compressive strength of concrete using recycled aggregate has a negative correlation with the amount of mortar particles, since mortar particles cause fragile parts in hardened concrete, so the compressive strength of concrete in the seal curing trend to be lower than in standard curing.(3) The compressive strength of concrete using high-quality recycled coarse aggregate concrete was about 20% lower than crushed stone. The ratio was increasing steadily in the case of the high strength concrete. It was due to the fragility of the mortar particles, as well as the different of surface structure on aggregate and shape of them between recycle aggregate and crushed stone.(4) The Young’s Modulus of recycled aggregate concrete decreases depending on the amount of mortar particles in recycled coarse aggregate, as well as the compressive strength. The relationship between the compressive strength and the Young’s Modulus of high-quality recycled coarse aggregate concrete can be evaluated by the formula of Architectural Institute of Japan.