Effects and mechanisms of incorporated nanoparticles on the rheological performance of cement pastes

Understanding the effects of nanoparticles (NPs) on rheological performance of cement pastes is of great importance to predict the hardened properties of concrete with NPs. In this study, several representative NPs, including nano silica (NS), nano titanium dioxide (NT), and nano zirconia (NZ), were employed to study the influences of their surface physicochemical characteristics (active and non-active, specific surface area (SSA), and lipophilic and hydrophilic) on the rheological parameters of cement pastes. The rheological behaviors of cement pastes were characterized by four rheological parameters including yield stress (& tau;0), flow index (n), minimum viscosity (& eta;min), and critical shear rate (& gamma;cri). H-B model was chosen to calculate the yield stress of the cement pastes with/without NPs. The results demonstrated that surface physicochemical characteristics of NPs can affect the rheological parameters of cement pastes. The minimum viscosities of cement pastes incorporating all types of NPs demonstrate a trend of decrease first and then increase with increasing shear rate. Cement pastes incorporating NS have the largest yield stresses and the minimum viscosities compared with those incorporating NT and incorporating NZ. Meanwhile, in terms of surface characteristics of NPs, cement pastes with lipophilic NS have lower yield stresses and minimum viscosities than those with hydrophilic NS. In addition, with the increasing NP dosage, the critical shear rate of cement pastes with active NS increases, while those of cement pastes incorporating non-active NT and NZ almost remain unchanged. A viscosity prediction model of cement pastes with NPs was established, which has higher accuracy and can predict the viscosity of cement pastes at low NP dosages compared with the modified classical viscosity prediction models. Furthermore, the water film thickness of NPs calculated using the established viscosity prediction model may provide guidance for internal curing of hardened concrete incorporating NPs.