Suitability of recycled concrete aggregate for use in BS 5328 designated mixes

The paper describes a study undertaken to examine the suitability of recycled concrete aggregate (RCA) for use in BS 5328 designated mixes. The results for the aggregate characteristics showed that plain as well as reinforced demolished concrete debris can be crushed using existing plant to provide RCA of physical properties that satisfy the current BS 882 requirements. The density of both fine and coarse RCA was found to be lower than that of natural aggregate (NA) and water absorption was three to six times higher. The results showed that original strength of the recycled concrete had a negligible effect on the fresh properties of the designated concrete mixes produced. Those mixes with high proportions of RCA were found to be harsh or less cohesive and exhibited higher bleeding, but this could be overcome using a filler material, such as coarse PFA, The test results also indicated that up to 30% coarse or 20% fine RCA had no effect on the strength of concrete, but thereafter there was a gradual reduction in strength with increase in RCA content. A method for taking account of strength reductions with RCA concrete was proposed, which involved simple adjustment to the water/cement ratio. Studies of concrete durability, comprising (i) near surface absorption, (ii) carbonation rates, (iii) sulphate resistance tin nonaggressive conditions), (iv) freeze/thaw in mater and (v) abrasion resistance showed similar performance for RCA and NA concrete mixes of equivalent strength, The practical implications of the study for the construction industry are also considered.