Study on High-degree Recycled Aggregate for Concrete

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This report presents the results of series of studies conducted to determine the quality of high degree recycled aggregate made with heating & grinding method and its effects on normal and self-compacting concrete.High-degree recycled aggregates, made with heating and grinding method and free of adhered mortar on aggregate particles, satisfied the requirements for normal aggregates of Japanese Architectural Standard Specification JASS 5 for Reinforced Concrete work. Recycled aggregates, made with mechanical grinding method did not meet with the requirement of JASS 5 for normal aggregate, oven dry specific gravity being less than 2.4g/cm^3 and water absorption being higher than 4.0%due to adhered mortar, which causes deteriorating effects on drying shrinkage and durability of concrete. The allowable maximum value of adhered mortar content was found to be 15% for the specified oven dry specific gravity of 2.5g/cm^3 and water absorption of 3.0%. Concrete containing high-degree recycled ag … More gregates with higher percentage of solid volume as much as river gravel has the equivalent strength and durability as those with crushed stone. And water content and drying shrinkage were lower and modulus of elasticity of concrete was higher than those of crushed stone concrete. High-degree recycled aggregate was found to be applicable for self-compacting concrete, with higher fluidity, lower binder content, lower dosage of super-plasicizer, lower drying shrinkage and higher modulus of elasticity than those of crushed stone concrete. By-product powder with the fineness of 400m^2/kg generated in the process of heating & and grinding can be applicable as additives for self-compacting concrete without significant adverce effects on concrete quality.Series of experimental studies were carried out to determine the properties of concrete containing high quality recycled aggregates on normal concrete and super-plasticized high-performance concrete. High quality recycled aggregate concretes showed lower water content than those with crushed stone of the same slump. Compressive strengths were equivalent to those with river gravel of the same water cement ratio and were 10% lower than those with crushed stone. Tensile strengths and moduli of elasticity were higher and drying shrinkage were lower than those with crushed stone. Less