Influence of different cement matrix on the static and dynamic mechanical properties of Ultra-High Performance Concrete

Sulphoaluminate cement (SAC) and aluminate cement (AC) have the advantages of lower CO2 emission, fast early strength development and excellent durability properties compared to Portland cement (PC). While Sulphoaluminate cement-based UHPC (SAC-UHPC) and aluminate cement-based UHPC AC-UHPC perform better in terms of dynamic performance, there are fewer studies in this area. Hence, this study investigates the carbon footprint, workability, static and dynamic mechanical properties, porosity, physical phase composition and microstructure of UHPC prepared from PC, SAC, AC. The results show that AC-UHPC and SAC-UHPC can reduce CO2 emissions by 195.92 kg/m3 and 110.09 kg/m3 respectively, compared to portland cement- based UHPC (PC-UHPC); the workability of AC-UHPC with a slump flow of 720 mm is better than that of SAC-UHPC and PC-UHPC. SAC-UHPC and AC-UHPC have excellent early static mechanical properties, the compressive strength of SAC-UHPC reaches 76.3 MPa at the age of 3 days, while PC-UHPC is 54.8 MPa, showing a difference of 21.5 MPa, which is approximately 39 % higher. When the strain rate was 107.1 s-1, the highest peak stress of AC-UHPC reached 158.4 MPa, and its impact toughness was measured at 240.5 J/m3. SAC-UHPC is weaker than PC-UHPC and AC-UHPC in the terms of dynamic compression resistance, but it shows good deformation capacity and impact toughness under different strain rates, respectively. The difference in porosity among the three samples does not exceed 1 %. The hydration products of PC-UHPC are dominated by Ca(OH)2 and C-S-H, while SAC-UHPC are dominated by ettringite (AFt), and ACUHPC are dominated by CAH10, C2AH8, and C3AH6. Hence, employing SAC and AC in the production of UHPC is a viable approach that can substitute traditional PC-UHPC, leading to lowing cement required, energy conservation and CO2 emissions reduction.