Characteristics of Portland blast-furnace slag cement containing cement kiln dust and active silica

This investigation dealt with the effect of active silica, silica fume (SF) or rice husk ash (RHA), on the mechanical and physico-chemical characteristics of the hardened blended cement pastes made of Portland blast-furnace slag cement (PSC) containing cement kiln dust (CKD) cured under normal conditions. Two blends made of PSC and CKD, improved by SF and two blends made of PSC and CKD improved by RHA were investigated. Hardened blended cement pastes were prepared from each cement blend by using water/cement ratio (W/C) of 0.30 by weight and hydrated for various curing ages of 1, 3, 7, 28 and 90 days at the normal curing conditions under tap water at room temperature. Each cement paste was tested for its physico-chemical and mechanical characteristics; these characteristics include: compressive strength and kinetics of hydration. The phase composition of the formed hydration products was identified using X-ray diffraction (XRD) and differential thermal analysis (DTA). It was found that the partial substitution of PSC by 10% and 15% of CKD is associated with an increase in the rate of hydration and a subsequent improvement of compressive strength of hardened PSC-CKD pastes. In addition, the replacement of PSC, in PSC-CKD blends, by 5% active silica was accompanied by further improvement of the physico-mechanical characteristics of the hardened PSC-CKD pastes.