Microstructural InvestigationI of Portland Cement Mortars Containing Varying Dosages Polynaphthalene Sulfonate Superplasticizer

The effect of varying dosages of a polynapthalene sulfonate (PNS) superplasticizer on the microstructure of a portland cement paste, and on the microstructural and transition zone characteristics of a portland cement mortar, was investigated using AC impedance spectroscopy. Interpretation of the impedance and resistivity data was carried out in conjunction with data from mercury intrusion porosimetry, scanning electron microscopy, and other techniques. The addition of the PNS superplasticizer influences both the cement paste/sand interfacial region and the bulk paste component in the mortar. The transition zone was more porous at early hydration (around 4 hours) for mortars with high dosages of superplasticizer. The dosage levels also influence the morphology of the hydrates. Larger high frequency arcs and higher electrical resistance values were obtained for all the superplasticized mortars at one day and beyond. This suggests a modification in the pore structure and porosity of both the transition zone and the bulk paste due to presence of the superplasticizer. Mercury porosimetry, thermogravimetry and conduction calorimetry measurements support the interpretation of the AC impedance spectra.