RESEARCH ON THE RECYCLED AGGREGATES FOR CONCRETE IN NUCLEAR POWER PLANTS: Characteristics of high quality recycled coarse aggregates depending on manufacturing methods

Several Nuclear Power Plants established 5 decades ago have been faced on decommissioning process in Japan. The amount of concrete wastes generated from demolished Nuclear Power Plants are about 5 hundred thousand tons for a typical 1,100Mw class unit. Basically Nuclear Power Plants were used advanced and controlled concrete which met Architectural Standard Specification JASS 5N ”Reinforced Concrete Work at Nuclear Power plants”. Even if demolished concrete include quality controlled aggregates, they will be reclaimed without using for load material. Research and developing about recycle aggregate concrete started at 1974, first almost all of studies were connected to mix proportion and strength. But studies about quality controlled of recycle aggregates have increased in perspective of durability of concrete with recycled aggregate. Architectural Institute of Japan standardized the use of high quality recycle aggregate in Architectural Standard Specification, JASS 5 “Reinforced Concrete Work” in 2003, and Japanese Standards Association specified Japan Industrial Standard, JIS A 5021” Recycled Aggregate for Concrete Class H” in 2005. This paper presents that 5 high-quality recycled coarse aggregates were produced from two types of demolition concrete, and the characteristics of different methods and the effects of raw material were investigated through experimental studies. ・Five types of recycled coarse aggregate met to JASS 5N or JIS A 5021. ・The grain size distribution of recycled aggregate differs depending on the method, and the volume around 15 mm increased more than other sizes. ・Despite the ratio of adhered mortar was less than 20%, there was a strong correlation between the oven-dry density and the ratio of adhered mortar, between the ratio of water absorption and the ratio of adhered mortar. ・Only the mortar particles were contained in the recycled aggregate because the strong mortar particles were not destroyed and eventually generated mortar particles with friction surface. ・Measuring the amount of mortar particle was efficient and convenient to check the quality of recycled coarse aggregate in manufacturing process. ・Demolished concrete from Nuclear Power Plants was appropriate for raw material to produce high quality recycle aggregate due to confirm profile of original concrete and characteristic of original aggregate. The results were found to be acceptable for Nuclear Power Plants and the use of high quality recycled aggregates have been sp