Effect of sodium silicate as activator on the fresh and hardened properties of cement-slag blended paste

Abstract

Ground granulated blast-furnace slag (GGBS) is commonly used as partial cement replacement in concrete production. Although the use of GGBS has many advantages, it possesses a lower initial hydration rate that leads to lower early strength. Therefore, an attempt to use sodium silicate to activate the GGBS was carried out to promote the early strength of cement-GGBS blended paste. Based on experimental results, incorporation of 5 and 10% of sodium silicate slightly reduced the flowability and final setting time of blended paste. For hardened properties, the addition of sodium silicate reduced the strength at early age until 28 days. The modulus of elasticity of activated paste with sodium silicate was lower at early age, however at 28 days the result was comparable with the control specimen. The addition of sodium silicate decreased the ultrasonic pulse velocity (UPV) value at early age, however, at 28 days, 5% sodium silicate specimen had a higher UPV value than the control specimen. The different trend between UPV test and compressive strength test was suggested due to the inhomogeneous structure of activated blended paste that had a different mechanism during destructive test (compressive strength test) and non-destructive test (UPV test).