Abstract
This study was conducted to investigate certain characteristics of tuff and volcanic ash quarried from Mt. Elgon and Mt. Rwenzori in Uganda that may render the materials beneficial for use in industrial applications as pozzolans. Both tuff and volcanic ash materials were ground and blended with Portland cement at varied replacement levels and tested for several properties. It was found that incorporation of 20 to 25% volcanic ash gave the highest compressive strength and substantially reduced alkali-silica reac-tivity. The ash met ASTM requirements for ‘Class N’ pozzolans. This study suggests that the volcanic ash, when ground to 506 m2/kg Blaine fineness develops high quali-ties for potential use as a mineral admixture in cement and concrete. Conversely, the use of tuff was found to significantly increase alkali-silica reaction. This reiterates the possible harmful effects of some pozzolans to concrete if used without precaution, dis-cretion or thorough understanding of their characteristics.