Abstract
The influences of polycarboxylate (PCE) superplasticizer on pore structure of hardened cement pastes (HCPs) and impermeability of hardened mortars were investigated. Cement pastes and mortars with different water to cement ratios (W/Cs) and varied superplasticizer dosages were prepared and cured for 7 days and 28 days respectively. Mercury intrusion porosimetry and alternating current impedance (ACI) were employed to characterize the pore structure of HCPs and the impermeability of hardened mortars. Results show that PCE significantly affects the pore structure of HCPs due to its impacts on the dispersion of cement grains in fresh cement pastes. The effects of superplasticizer on the pore structure are associated with W/C and curing age of cement pastes. At W/C of 0.29, increasing superplasticizer dosage results in obvious declines in total pore volume at early ages and reduces pore connectivity. By contrast, increases in total pore volume and higher pore connectivity are found when PCE is incorporated in the paste at W/C of 0.4. ACI reveals that the inclusion of PCE brings about a denser structure and enhanced impermeability of hardened mortars. It is believed that the enhanced impermeability is related to the reduced interfacial heterogeneity and the compacted interfacial zone when PCE is added.
