Strength, permeability and microstructure of self-compacting concrete containing rice husk ash

Abstract

Self-compacting concrete (SCC) is characterized by deformability and segregation resistance. It flows under its own weight while remaining homogeneous in composition. This study presents the effect of replacing cement content with rice husk ash (RHA) as supplementary cementitious materials (SCM's) in SCC and observing fresh flow (slump flow, V-Funnel, U-box, L-Flow), mechanical strength (compressive and split tensile) and durability properties (porosity and rapid chloride permeability test) at 7, 28 and 56 d. Concrete specimens were prepared with 0, 10, 15 and 20% RHA replacing cement. 20% RHA replacement showed minimum specified workability. An increase of about 25% strength at 7 d, 33% at 28 d and 36% at 56 d was observed with RHA content of 15% RHA when compared to control mix. Maximum split tensile strength was 3.8 N mm−2 at 28 d and 4.0 N mm−2 at 56 d for 15% RHA replacement. The inclusion of RHA as partial replacement to cement improved the strength properties and durability properties that remained within limits up to 20% replacement. All the mixes were less porous as compared to the control mix at all ages and showed “low range” to “very low range” chloride penetration also. Microstructure (scanning electron microscopy, SEM and X-ray diffraction, XRD) analysis of 15% RHA replacement showed dense formation of C-S-H gel which is the root cause of the increase in strength.