Mechanical properties and mechanism of nano-CaCO3 enhanced sulphoaluminate cement-based reactive powder concrete

This paper investigated the properties of sulphoaluminate cement-based reactive powder concrete (RPC) incorporated with nano-CaCO3 (NC), including setting time, fluidity, strength, hydration, and microstructure. The results showed that the addition of NC shortened the setting time and reduced the fluidity of RPC mortar. The rate of heat flow and the cumulative heat of hydration increased along with the increased NC content, and reached the maximum when the NC content was 2.5%. Moreover, the addition of NC enhanced the compressive and flexural strengths of RPC. When the NC content was 2.5%, the experimental group's 90d compressive and flexural strength increased by 25.8% and 19.9%, respectively, compared with the blank group. The results of XRD, TG, ICP and isothermal calorimetry had a good consistency and revealed the mechanism of NC promotes the hydration process of RPC, i.e., more hydration products, such as AFt and AH(3), were formed owing to the sufficient ion exchange in earlier ages, which filled the pores and made the RPC microstructure more compact and the mechanical properties better.