Rice husk ash for alkali activation binary blends (fly ash/blast furnace slag)

Alkali activated mortars made of class F fly ash and blast furnace slag were cast, in order to study the effect of an alternative source of silica on its properties of fluidity and compressive strength. Rice husk ash and sodium silicate solution, mixed with sodium hydroxide, were used for activation of mortars. The mineralogical and structural information of alkali activated systems was obtained by X-ray diffraction (XRD), while the analysis of fresh properties was carried out by means of fluidity test. The mechanical properties of mortars were assessed by 28 days compressive strength test. It was found that mortars activated with rice husk ash plus sodium hydroxide showed compressive strengths up to 25% higher that those activated with sodium silicate / sodium hydroxide. Finally, equations were proposed for the prediction of compressive strengths of mortars according to the type of activator. This study concludes that it is possible the use of rice husk ash as an alternative source of silica in alkaline activation process.