To overcome performance deficiencies of the raw mordenite-rich tuff in the partial replacement of Portland cement in cement paste, the material was subjected to different treatments: calcination at 300 °C and 500 °C, grinding to very high specific surface areas, co-grinding with Portland cement, and separate or co-grinding with granulate blast furnace slag. The resulting materials were examined by tracking changes in density, particle shapes, and size distributions. The blended cement pastes were examined by monitoring the water demand, setting time, hydration process by isothermal microcalorimetry, degree of hydration, non-evaporable water content and free Ca(OH)2 by TGA-DSC analysis. The findings provide clear evidence that with the activation techniques, the performance of the raw mordenite-rich tuff is improved.