Physico-chemical characteristics of blended cement pastes containing electric arc furnace slag with and without silica fume

Filled-pozzolanic cement pastes were made by different replacements of OPC by electric arc furnace slag (EAFS) with silica fume (SF) at water/cement ratio of 0.27. The pastes were hydrated up to 90 days. At each time interval, the physico-chemical characteristics of the hardened cement pastes were studied and related to the structure of the hardened pastes and the role of EAFS replacement as a filler in the hardened OPC-EAFS pastes. It was found that the optimum replacement of OPC by EAFS for the improvement in hydraulic properties of filled cement pastes is 6%. High replacement of OPC by EAFS (10% or 15%) causes a notable deterioration in the compressive strength at all ages of hydration. The replacement of EAFS in Mix (90% OPC + 10% EAFS) by 4% SF causes a marked improvement in the mechanical properties for the hardened pastes of Mix (90% OPC + 6% EAFS + 4% SF). The DSC thermograms for all pastes indicated the formation of nearly amorphous calcium silicate hydrates, calcium sulphoaluminate hydrates, calcium aluminate hydrates and portlandite. The SEM micrographs showed that the partial substitution of OPC by EAFS and/or SF leads to more dense structures as compared to the neat OPC paste.