Properties of Locally-Sourced Rice Husk Ash (RHA)-Blended Mortar

The present study is aimed to investigate the effects of different proportions of locally sourced RHA in Vietnam on the mechanical properties, microstructure and porosity of cement mortar. RHA is a material that was used to replace the original Portland cement (OPC). Prisms of dimensions of 40x40x160mm were cast and cured in water to determine the flexural and compressive strengths at 7 days and 28 days. The porosity was studied by Mercury Intrusion Porosimetry (MIP), while the microstructure of RHA mortar was determined by Scanning Electron Microscope (SEM). The results show that RHA reduces the workability of fresh mortar unless water reducing admixture is added, due to the porosity of RHA leading to an increase in the surface area of RHA. The locally-sourced RHA reduces the strengths at 7 and 28 days; however, the strength improves with age due to the latent pozzolanic reaction between RHA and Ca(OH) 2 . In addition, 5% and 20% RHA both increase the effective porosity and cumulative intruded volume, while 10% RHA reduces those properties at both 7 days and 28 days. Keywords: mortar, rice husk ash, strength, microstructure, porosity.