Improvement on engineering properties and volumetric stability of alkali-activated slag-based composite cementitious material with rice husk ash and magnesium oxide

Abstract

This study used rice husk ash (RHA) and magnesium oxide (MgO) to improve the engineering properties and volumetric stability of alkali-activated slag-based cementitious material. Experimental results found that when the amount of slag substituted by RHA increased from 0% to 20%, the initial setting time was extended from 15 to 20 min, and the final setting time was shortened from 35 to 30 min for the paste without MgO. The optimal substitution amount of RHA was 10%, which had the maximum compressive strengths at ages of 28 and 56 days to achieve 104.44 and 102.43 MPa for the paste without MgO, respectively. The drying shrinkage of paste without MgO increased with both the increase of RHA from 0% to 20% and ages from 3 to 56 days. With RHA, the drying shrinkage substantially decreased with the substitutions of MgO from 0% to 2.0% and almost remained steady after ages of 7 or 14 days. The optimal amount of RHA to replace slag was less than 10% and the optimal content of MgO was less than 1%, which can effectively improve the volumetric stability and reduce the heat of hydration of paste.