Effects of Municipal Solid Waste Incinerator Fly Ash Slag on the Strength and Porosity of Slag-Blended Cement Pastes

This study investigates the relationship between porosity and compressive strength of slag-blended cement pastes and mathematical models that describe this relationship with different water-to-binder (w/b) ratio for different hydration ages. The strength and porosity of cement pastes containing fly ash slag from municipal solid waste incinerators (MSWIs) were compared to ordinary Portland cement pastes blended using different w/b ratios. Different percentages of OMIT MSWI fly ash/slag were utilized to determine the effects of slag content on the strength-porosity relationship. A low fly ash slag replacement ratio reduces compressive strength for up to 28 days. The cement pastes with slag with a low w/b ratio and low fly ash slag replacement ratio had a high compressive strength. The positive effect of incorporating slag into blended pastes is that the volume of fine pores increases as curing duration increases. A positive correlation exists between the development of compressive strength and porosity. The strength-porosity equation for the cement paste with slag is best explained using an exponential function (Ryshkevitch) with a correlation coefficient of 0.85. Compressive strength and porosity at different curing ages depend on fly ash slag content and the w/b ratio of the paste.