Dispersion mechanism in processing in cement paste

The effects of superplasticizers, sulfonated naphthalene formaldehyde condensate (SNF) and carboxylated acrylic ester (CAE) copolymers, upon rheological properties of cement pastes have been investigated. Two types of CAE were used in this study. CAE1 (AA1) had a lower number of side chains than CAE2 (Advaflow). In each case, there was a critical superplasticizer concentration (Phic) above which the rheological properties were observed to transition from strongly shear thinning to Newtonian flow behavior. The critical concentrations of SNF and CAE1 were approximately 0.8wt% at w/c ratios of 0.35 and 0.30, and approximately 1.25wt% at a w/c ratio of 0.25, whereas those of CAE2 were approximately 0.4wt% at all of those w/c ratios. The time-dependent flow properties of these pastes exhibited dramatic differences above and below Phic. Such changes were found to correlate with the respective abilities of these superplasticizer additives to retard cement hydration, as determined by Si-29 NMR spectroscopy.