Coarse recycled aggregates for use in new concrete

The results of a laboratory experimental programme aimed at examining the performance of Portland-cement concrete produced with natural (gravel and sand) and coarse recycled aggregates (RA) are reported in this paper. All concrete mixes were designed for equivalent 28-day compressive cube strengths of 20, 30 and 40 N/mm². The effects of up to 100% coarse RA on fresh, engineering and durability properties have been established and its suitability for use in a range of designated applications assessed. The results for the fresh concrete showed a reduction in workability of the concrete with increase in RA proportion beyond 30% in the mix, although the slump measurements remained within the allowable margins of ±25 mm. The mixes with high proportions of RA were found to be less cohesive and exhibited slight bleeding. Studies of hardened concrete properties, comprising bulk engineering properties (compressive cube strength, flexural strength, modulus of elasticity, drying shrinkage) and durability (initial surface absorption, carbonation rates, freeze–thaw in water and abrasion resistance) showed similar performance for RA and natural aggregate concrete mixes of equivalent strength.