Effects of steel fibre and silica fume on impact behaviour of recycled aggregate concrete

Abstract

This paper presents the effects of silica fume and steel fiber on the mechanical properties and impact behavior of recycled aggregate concrete containing two types of recycled coarse aggregates (RCAs). In total, 20 series of concretes are considered and they are divided into 4 groups. The first group consisted of 1 control concrete containing natural coarse aggregate and 4 control recycled aggregates concretes containing 50 and 100% RCA of two types (A and B). The second and third series are similar to the first series in every aspect except the former contained 8% silica fume as partial replacement of ordinary Portland cement and the latter contained 1% steel fiber by volume. In the fourth series, both 8% silica fume and 1% steel fiber are used. Compressive and split tensile strengths of all concretes are measured in terms of mechanical properties evaluation and low velocity impact hammer test is conducted to evaluate the impact behavior of all concretes. Results show that the concrete containing RCA obtained from high strength parent concrete exhibited better mechanical properties than that containing RCA made low strength concrete. The addition of silica fume improved the split tensile and compressive strengths of recycled aggregate concretes containing both types of coarse aggregates. The addition of steel fibers significantly increased the compressive and split tensile strengths of all concretes, especially recycled aggregate concretes. The simultaneous use of silica fume and steel fibers had a significant effect on the compressive and split tensile strengths of all recycled aggregate concretes, probably due to better bond of steel fibers with mortar containing silica fume as well as improved ITZ between RCA and mortar. The addition of 100% RCA of both types significantly reduced the impact resistance of recycled aggregate concretes. The same is also true even when silica fume is added. The addition of steel fibers significantly improved the impact behavior of recycled aggregate concretes. The addition of silica fume, however, did not show any significant improvement in impact resistance of steel fiber-reinforced recycled aggregate concretes.