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Synopsis Effects of using recycled concrete of different qualities as coarse aggregate upon the strength and deformation of concrete are reported. Tests on the aggregates showed that the recycled concrete aggregates have lower specific gravity and higher absorption capacity than the original crushed granite aggregate. The resistance to mechanical actions such as impact, crushing and abrasion for the recycled concrete aggregates is also lower. The effects of using recycled concrete aggregates instead of natural aggregates in concrete are: reduction in compressive strength up to 25%; reduction in modulus of elasticity up to 30%; improvement in damping capacity up to 30%; and higher amounts of drying shrinkage and creep. Available methods of predicting the modulus of elasticity on the basis of compressive strength for conventional concrete overestimate the modulus of elasticity for recycled-aggregate concretes.

Synopsis The effects of using crushed concrete as coarse and fine aggregates upon strength and deformation of concrete are reported. The properties of recycled aggregates differ from those of natural aggregates due to the presence of a considerable proportion of mortar attached natural aggregate and loose mortar. For a medium strength concrete, the results show that strength and modulus of elasticity are reduced by about 10% and 35%, respectively, whereas drying shrinkage is nearly doubled when recycled aggregates are used instead of natural aggregates in comparable mixes. The efect of recycledfine aggregate on the deformational properties is less than that of coarse aggregate. Fresh concrete properties are only marginally affected by the use of recycled aggregates.

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