The effects of rice husk ash (RHA) and fume silica (SF) in both binary and ternary systems on the properties of cement pastes and the compressive strength of concretes were studied. The amount of cement replacement in both systems was 15%. The free calcium hydroxide (Ca(OH)(2)) content was analyzed using XRD and TG/DTA for the hardened cement pastes. The results showed that the amount of Ca(OH)(2) decreased significantly the curing ages for all blended cement pastes. At 28 days, the amount of Ca(OH)(2) in OPC is 17.31%, 8.18% in RHA and 6.43% in SF replacements, respectively. The ternary system similarly indicates a significant reduction of Ca(OH)(2) content. The compressive strength of concretes was improved significantly by blending the aforementioned materials in both systems. In the ternary system, the concretes containing 7.5% SF and 7.5% RHA gave remarkable improvement in the compressive strength. For example after 90 days curing, the strength is 57.8 MPa whilst only 47.5 MPa for OPC. Therefore, the application of proper ratios of RHA and SF in a ternary system is able to increase the properties of the concrete.

Keywords: Ternary system; Ca(OH)(2); Blended cement; Silica fume; Rice husk ash