This study investigated the effects of using unprocessed rice husk ash (RHA) and silica fume as partial replacements for cement in concrete. Cylinders and cubes were cast with RHA and silica fume replacing cement at levels from 10-25%. Testing found that RHA increased splitting tensile strength by up to 14% at 15% replacement, while silica fume increased strength by 17% at 20% replacement. Combining RHA and silica fume did not significantly improve strength over the control mix. The results indicate that RHA and silica fume can be used individually as supplementary cementitious materials in concrete to increase strength.