Retardation effect and corrosion detection of blended cement pastes

Different blended cement pastes were prepared from OPC + 10%, 20% and 30% slag (air cooled) by using a water/solid ratio (W/S) of 0.25 (by weight). The hydration was conducted for various time intervals at 1, 3, 7, 28 and 90 days. Each hardened cement paste was tested for its physico-chemical and mechanical characteristics under normal curing conditions. In addition, the phase compositions of the formed hydration products were identified by means of X-ray diffraction (XRD). Moreover, the electrical conductivity and corrosion detection measurements were also carried out for all the previous blended cements under investigation. The results showed that the combined water contents increase gradually with hydration time for all hardened cement pastes and the partial replacement of OPC by slag cause a notable drop in the combined water content for all blend pastes. The compressive strength values obtained for the hardened blended cement pastes is less than that of neat OPC pastes at all ages of hydration up to 90 days but the sample with 30% slag + 70% OPC had the highest compressive strength. The electrical conductivity of the studied blended cement pasts was lower than that of OPC due to less alkali hydroxides when cement is diluted by the added slag. The significance of low potentials of steel bars in these pastes indicates inhibition of corrosion. As a result, it can be concluded that the mineral admixtures retards the hydration and inhibit the corrosion for cement pastes