Effect of nano-metakaolin on the thixotropy of fresh cement paste

Abstract

• Nano-metakaolin increases the thixotropy of fresh cement paste. • The maximum thixotropy of cement pastes occurs in the temperature range of 25–30 °C. • The thixotropy of NMK cement pastes shows an increasing trend with the hydration time. • The thixotropy of NMK cement pastes increases linearly with the yield stress. Nano-metakaolin (NMK) was used to increase the viscosity of fresh cement pastes and the mechanical properties and durability of hardened cement-based materials. However, the effect of NMK on the thixotropy of fresh cement pastes was not systematically investigated. The paper investigates the thixotropy of NMK cement pastes, the effects of superplasticizer, NMK content, hydration time, and environmental temperature were considered. The size of the flocculation structures (flocs) of the NMK cement pastes was measured, and the hysteresis loop area of the NMK cement pastes was identified. The relationships between the hysteresis loops area and yield stress, packing density, and particles spacing of the NMK cement pastes were established. The results showed that the incorporation of NMK increased the thixotropy of fresh cement pastes with and without superplasticizer addition. NMK significantly increased the thixotropy of the cement pastes with superplasticizers addition. The thixotropy of NMK cement pastes firstly increased and then decreased within 10 – 45 °C, the maximum thixotropy appeared at around 25–30 °C. The thixotropy of the NMK cement pastes exhibited an increasing trend with the hydration time. The thixotropy of the NMK cement pastes linearly increased with the yield stress. The hysteresis loop area decreased with the increase of the packing density and particles spacing.