Accelerated Early Age Hydration of Cement Pastes Blended with Sulphoaluminate Expansive Agent

Abstract

Addition of sulphoaluminate expansive agent could be one useful method to reduce the shrinkage crack destruction of shotcrete. While the setting and hardening behavior and early age mechanical strength of cement pastes containing liquid setting accelerators may be influenced by the introduction of sulphoaluminate expansive agent (SEA). Therefore, in this work, the early age hydration behavior of different accelerated cement pastes with SEA was investigated via setting times measurement, early age mechanical strength test, isothermal calorimeter, mineralogical composition, thermal gravimetric analysis (TGA) and scanning electron microscope with EDS detection. Results showed that the ability of liquid setting accelerators on shortening the setting times of cement pastes could be enhanced by the addition of SEA, especially for alkali-free type accelerator due to the prompted formation of massive rod-like ettringite phase. In addition, the further hydration extent of C3S phase in accelerated cement pastes was advanced by more dissipative portlandite phase to form such massive rod-like ettringite, thus improving the initial mechanical strength.