ABSTRACT
Hardening of calcium hydroxide and calcium silicate binders composed of cement, rice husk ash (RHA) and lime in different compositions were studied with mortars using thermal analysis, mechanical strength and SEM. When cement is partially replaced with RHA and lime, hardening occurs as a result of combined hydration, pozzolanic reaction and carbonation reaction. While hydration of cement contributes to the early strength development of the mortars, carbonation is much more pronounced at later stage with the decrease in the cement content and increase in the porosity of the mortars. RHA-cement mortars indicated a long-term strength development, which is lower than that of the reference cement mortar. This was attributed to their higher porosity due to the high water demand of the porous RHA grains. Strength reduction was recorded at the very early stage for RHA-cement-lime mortars containing 10%-wt cement as well as RHA-lime mortars. This has been explained with the insufficient cement content, destructive effect of the calcium carbonate phases on the initially hydrated cement phases and partial carbonation of the initially hydrated phases. This decrease can also be related to the presence of excess RHA in the matrix as excess silica can react with the initially formed C-S-H phase, which can lead to the formation of polymerized C-S-H phase.
