Effect of fly ash-gypsum blend on porosity and pore size distribution of cement pastes

This paper reports results on the porosity and pore size distribution (PSD) of cement paste containing simulated desulphurised waste (SDW). The SDW was chosen due to the variability in chemical composition of real desulphurised waste. The SDW is a combination of fly ash and gypsum. The content of fly ash in the SDW changed from 0 to 100% by weight. The water to binder ratio was 0.5. The binder consists of cement and SDW. Cement in the pastes was partially replaced with 25 wt-% SDW. The porosity and PSD of cement pastes at 28 days of curing is reported. Increasing amount of gypsum does not seem to greatly change the pore volume; however, there is tendency of obtaining coarser pore structure in the presence of gypsum. The compressive strength increases with increasing amounts of gypsum. Correlation between strength and PSD is conducted.