Effects of different cementitious materials and accelerators on the flexural and compressive behaviors of SUHPC

The combination of various cementitious materials can effectively mitigate early-age cracking and flowability issues in concrete that arise from the use of accelerators during the spraying process of sprayed ultra-high-performance concrete (SUHPC). Flexural and compressive strengths serve as critical indicators for evaluating the mechanical performance of SUHPC. This study investigates the effects of various types of cementitious materials, including Portland cement, calcium aluminate cement (CAC), and gypsum (CaSO₄·2H₂O, abbreviated as C$), as well as alkali-free accelerators, on the flexural and compressive properties of SUHPC. The results show that partial replacement of Portland cement with CAC alone leads to a significant reduction in flexural and compressive strength, with the greatest decrease observed at a CAC dosage of 30%. In contrast, in a ternary binder system incorporating both CAC and C$, increasing the C$ content from 0 to 15 wt% enhances the flexural and compressive strengths, reaching maximum values of 21.5 MPa and 123.7 MPa, respectively. The incorporation of CAC negatively impacts the flexural and compressive properties of SUHPC. However, the incorporation of C$ in the ternary binder system effectively offsets the adverse effects of CAC, leading to improvements in toughness and energy absorption capacity. While alkali-free accelerators enhance early-age strength, such admixtures tend to impair long-term mechanical performance. This degradation can be mitigated through the strategic combination of multiple cementitious components.