Hydration and Engineering Properties of Mechanically-Activated Composite Cement from Processed Steel Slag and Limestone

The aim of the present research work is to evaluate the feasibility of processing and utilizing steel slag in binary and ternary cement blends with limestone. The physical and microstructural properties of binary and ternary composite cements produced by inter-grinding mixtures of ordinary Portland cement clinker, processed steel slag and limestone in a laboratory ball mill with replacement levels varying from 0 wt.% to 30 wt.% were studied. The effects of processed steel slag and limestone incorporation on density of dry cement mixes and water consistency, setting time and volume stability of fresh and hardened cement pastes were investigated. Also, density, water absorption, total open pore volume (%) and compressive strength of cement mortars were measured. The mix with 15 wt.% limestone and 15 wt.% processed steel slag was selected as a typical ternary cement mix for complementary studies including X-ray diffractometry, thermal gravimetry, Fourier-transform infrared spectroscopy, and scanning electron microscopy analyses. The results show that removal of relatively high metallic content of steel slag increases its grindability for mechanical activation and improves its hydraulic properties effectively and makes it suitable for being recycled in cement industry. The results show that mechanical activation of the cement mixes enhances the poor hydraulic activity of the processed steel slag and compensates the strength loss to some extent. The physical and chemical properties of all studied composite cement mixes comply with ASTM standard specifications, except the compressive strength of the cement mixes at 28-days containing 20 wt.% or higher amounts of limestone ground to the relatively low Blaine specific surface area of about 3000 cm2/g.