Effect of silica fume on recycled aggregate concrete

The ever increasing concrete usage has raised concerns over its environmental impact because when reaching the end of the design life, concrete waste usually ends up as landfill. This creates a significant problem because of the difficulties associated with managing the increased volume of concrete waste. As a result, use of recycled concrete to replace the coarse aggregate has attracted attention as it can reduce the amount of landfill as well as requirement of virgin aggregate. Past studies have indicated some bonding issues of recycled concrete aggregate (RCA) at the interfacial transition zone (ITZ) preventing usage of material in structural concrete applications. The main objective of this investigation was to determine whether compression and flexural strength improvements could be gained with the addition of silica fume in the concrete mix. It was hypothesised that silica fume's fine particles reduced the porosity of the RCA which should result in an increased modulus of elasticity and improve the bond at the ITZ. This paper presents an experimental investigation into the effect of replacement of virgin aggregate with recycled concrete aggregate (RCA) with the addition of silica fume on the compressive and flexural strength of a blended cement concrete. Varying amounts of silica fume was used in addition to 100% coarse aggregate replacement. The investigation indicated that favourable strength results are achieved with the addition of 10% silica fume in RCA.