Performance of portland/silica fume cement concrete produced with recycled concrete aggregate

The use of recycled aggregate in concrete industry has a great potential to reduce demand for natural aggregate and the amount of solid waste dumped at landfill sites. The main objective of this study is to design a concrete made with different proportions of coarse recycled concrete aggregate (RCA) having a similar 28-day design strength to corresponding natural aggregate concrete. Recycled coarse aggregates, obtained by crushing concrete debris from various sources, were used in three proportions of 30, 50, and 100% (by weight) to produce concrete with various water-cement ratios (w/c) and different compressive strength grades. The key mechanical properties and durability performance of concrete produced with portland silica fume (PSF) and RCA were investigated. The RCA used showed inferior mechanical properties (crushing and impact values) than the natural aggregates (NA) and, hence, RCA concrete exhibited slightly lower performance than NA concrete. The results showed that up to 30% coarse RCA had no major effect on the compressive strength of concrete and, thereafter, a gradual reduction in strength with an increase in RCA content was observed. Reducing the w/c of concrete treated with the RCA has led to an enhanced compressive strength, higher resistance to carbonation, and chloride ion ingress. It was also found that, when properly designed, portland cement silica fume (PC-SF) concrete made with different proportions of coarse RCA as substitute of NA may contribute to enhance the durability performance of concrete.