Hardening of mortars made from cement, rice husk ash and lime

Hardening of mortars composed of cement, rice husk ash (RHA) and lime in varying compositions were studied using thermal analysis, mechanical strength and scanning electron microscope. When cement is partially replaced with RHA, hardening occurs as a result of combined cement hydration, pozzolanic reaction and carbonation reaction. Although cement hydration contributes to the early strength development of the mortars, carbonation is much more pronounced at later stages with the decrease in the cement content and increase in the porosity of the mortars. Cement-RHA mortars indicate a long-term strength development which was lower than that of the reference cement mortar due to their higher porosity resulted from high water demand of the RHA grains. Strength reduction is recorded at the very early stage for cement-RHA-lime mortars containing 10 wt.% cement. This has been explained as being due to insufficient cement content and carbonation of the existing calcium silicate hydrate (C-S-H) phase.