Evaluation of residual rice husk ash reactivity

Rice husk ash (RHA) produced without burning control presents atomic arrangements characteristic of quartz and cristobalite, and amorphous silica structure which interact with calcium hydroxide (CH) to form calcium silicate hydrate (C-S-H). The depolymerisation of amorphous silica and the following precipitation of hydrated compounds depend on the pH of the aqueous solution, controlled by the dissolution of CH. The use of RHA in the production of pozzolanic cement requires prior understanding regarding the interaction of pozzolan with CH without the presence of Portland cement. This system establishes the maximum consumption of lime per amorphous unit of RHA. In this work, mixtures simulating 15% and 25% partial replacement of Portland cement by RHA were investigated. The evolution of the pozzolanic activity up to 182 days was measured and indicates the existence of remaining CH in both pozzolanic systems, regardless of the RHA content. However, the reaction rate of the pozzolan was higher in the system with higher CH content. Lime fixed by pozzolanic activity is not dependent on the ratio between CH and pozzolan.