Quality of Concrete containing Recycled Aggregate

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In search of ways to utilize waste concrete which is increasing year after year, a study was conducted on the quality of concrete in which recycled aggregate manufactured from crushed concrete was mixed as a part of the coarse aggregate. In this study the properties of the fresh and hardened concrete were examined experimentally with varying physical properties and proportions of the recycled aggregate.The Recycled aggregate showed differences in specific gravity, water absorption, and crushing values when compared with normal crushed stone. However, it was found that recycled aggregate can be used satisfactorily, if the proportions are carefully selected for the required quality and uses of the concrete. The results of the experiments showed that the use of up to 30% recycled aggregate causes no problem, unless high strength or high durability is required of the concrete. Within this range the concrete can be handled in the same manner as normal concrete. It was also revealed that the use of recycled aggregate for reinforced concrete members produces little adverse effect on the crack initiation load and the ultimate strength, if the concrete is proportioned to provide the same strength level as normal concrete.However, the foreign materials and excess mortar in the recycled aggregate could adversely affect the quality of concrete. Studies are planned for methods of removing foreign materials and mortar and for improved methods of crushing used concrete. Since waste concrete is anticipated to continue increasing, it should be regarded as a potential resource and be utilized efficiently, also for the sake of overloaded waste disposal grounds.