Methods to Mitigate the Negative Effects on Durability of Recycled Aggregate Concrete

Inspite of the improved understanding of many of the common causes affecting durability of recycled aggregate concrete, material failures due to chemical and physical attack are still of great concern to building and construction industry. Many studies have shown that using recycled aggregate in concrete suffers from durability problems caused mainly due to relatively porous residual mortar adhered to the surface of aggregate grains resulting in high water absorption, increase in permeability and shrinkage. Also the weaker interfacial transition zone (ITZ) of about 20–50 µm thickness around the aggregate particles, plays important role in reducing the bond strength between recycled aggregate and fresh concrete. These drawbacks have direct relevance in developing lower compressive strength and durability in recycled concrete and govern the penetration of deleterious substances in concrete by molecular diffusion and other transport processes, allowing access to carbonation, chloride ingress and sulfate attack. These shortcomings and negative effects on durability of recycled concrete can be mitigated with the use of proper mixing techniques, (i) using two-stage mixing process (ii) using high range superplasticisers and (iii) substitution of supplementary cementitious materials like metakaolin, flyash, slags and silica fume in recycled concrete.