Hydration characteristics of Portland cement – Electric arc furnace slag blends

Utilization of electric arc furnace slag (EAF slag) as blending material for Portland cement has been examined. This was done via the investigation of the hydration characteristic of EAF slag – Portland cement blended mixtures. Various ratios of EAF slag were used namely; 5, 10 and 20 wt% of solid mix. The hydration properties investigated for the various mixtures were; compressive strength, chemically combined water and free lime contents as a function of hydration times. The hydration ages were; 1, 3, 7, 28 and 90 days. In addition, phase composition of the formed hydrates was examined using XRD technique as well as differential thermal analysis (DTA) for some selected samples. The results showed that as the ratio of EAF slag increases the values of compressive strength decrease at all the hydration ages. Hydration kinetics of the investigated mixes was followed by determining the variation of free lime and chemically combined water contents with time of hydration. It was observed that hydration proceeds in four different stages. The values of chemically combined water of the cement pastes blended with EAF slag were less than those of the neat Portland cement paste at all hydration ages. The mode of variation of free lime content with time was nearly similar to that of combined water content. The results of chemically combined water, free lime, XRD analysis as well as thermal analysis were correlated well with those of compressive strength. All these results indicate that the used EAF slag has no significant pozzolanic reactivity.