CONCRETE RE-CYCLED. CRUSHED CONCRETE AS AGGREGATE

The author discusses the need for recycled concrete giving examples of Dutch practice where replacement of 20 per cent coarse aggregate giving C45 strengths is allowed. This amount does not affect the properties of fresh and hardened concrete. Replacement of up to 100 per cent should give strengths up to C25 and cause no problems in concrete with minor constructive requirements. Environmental factors and large increases in the cost of waste disposal has led to investigations into the re-use of material and more efficient methods of disposal. Materials are separated at the demolition stage and rubble is produced from used concrete and masonry. Research has led to regulations for the requirements of the materials; crushed concrete aggregate must contain more than 95 per cent of the material and crushed mortar must contain at least 65 per cent. Not more than one per cent may be of glass, wood, paper, textile etc. Several gradings are defined, the most common being 4mm to 32mm. The properties of the recycled aggregates are examined together with those of the fresh and hardened concrete mixes. The crushed mixed aggregates absorb more water than crushed concrete.