Synergistic effect of branched polymer/nano silica on the microstructures of cement paste and their rheological behaviors

Various branched polymers as superplasticizer containing nano silica were synthesized via in situ solution polymerization. The molecular structures of the branched polymers were characterized using 1HNMR and GPC methods. The interactions between the prepared polymers and nano silica were also investigated using TGA methods. After the neutralization and ultra sonication of the resulting nano suspensions possessing different amounts of nano particles, the size of the aggregated nano silica and branched polymers and their dispersion behavior were studied using DLS and SEM methods. The SEM results showed that the cement paste microstructure and morphology were different in the presence of the branched polymers and nano particles. The branched polymers influenced the cement microstructure and morphology of the hydrated calcium silicate crystals. In addition, the distribution of nano silica particles examined using EDAX method. The rheological properties of the cement pastes were examined at different water to cement ratios and pHs. The viscosity of the cement suspension was different depending on the concentration of the branched polymers as the superplasticizer and nano silica state. The branched polymer was desorbed from nano silica surface and then was adsorbed on the cement particle leading to decreasing the cement suspension viscosity and improving dispersion behavior of the cement particles.