Use of Recycled Coarse Aggregate for Prepacked and Postpacked Concrete

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The summary of research results on above mentioned title is as follows.1) Two types of original concrete were used and the strength levels were 250 and 570 kgf/cm^2. The first crush was done by a jaw crusher and the grading of the recycled coarse aggregate was adjusted to 15 to 40mm and 10 to 40mm. The physical properties of the recycled coarse aggregate A and B which were produced from the normal and high strength original concrete were classified into grade 2 and 3 respectively and were equivalent to low quality aggregate.2) The chemical admixtures for the grout mortar of replaced aggregate concrete was used, and the sand-cementitious material ratio of the mortar was 0.8 when the water-cementitious material ratio and mineral admixture-cementitious material ratio were 50 and 20% respectively and the flow time range was 16 to 20 seconds. Even if 5% of unit sand content was replaced by the 0.15mm under dust produced during crushing the original concrete, the flow time, bleeding ratio, expansion and compressive strength of the mortar were the same as the case of the non-dust mortar.3) The core test specimens were sampled from large scaled concrete block by a new purchased core boring machine. The compressive strength of the prepacked and postpacked concrete using recycled coarse aggregate was almost the same as the case of using gravel. The strength was not reduced by using the mortar with the dust and by changing the grading of the recycled coarse aggregate. The higher the strength level of an original concrete, the higher the compressive strength and dynamic Young's modulus of both concretes using recycled coarse aggregate.4) It was clarified that there was an every possibility of using the low quality recycled coarse aggregate and the dust produced by the low cursing energy for the prepacked and postpacked concrete.