Preparation of ecologically sustainable UHPC by replacing quartz powder with dolomite powder: Synergistic enhancement, microstructural evolution, and sustainability assessment

Ultra-High Performance Concrete (UHPC) has been widely used in major engineering projects due to its excellent mechanical properties and durability. However, the primary filler, Quartz Powder (QP), presents issues such as resource shortages, high energy consumption, health risks, and environmental pollution. Therefore, this study proposes replacing quartz powder with the industrial by-product associated waste Dolomite Powder (DP), aiming to address these challenges and promote the green and sustainable development of UHPC. A systematic evaluation was conducted on the effects of different DP incorporation rates (0%, 25%, 50%, 75%, 100%) on the macro-properties, microstructure, and eco-economical performance of UHPC. The results show that the flow spread increased by 20.27%. In terms of mechanical properties, the optimal performance was achieved with a 50% DP replacement rate, where the 28-day compressive strength and flexural strength increased by 5.53% and 4.66%, respectively, compared to the reference group. The setting time tests revealed that both initial and final setting times first increased and then decreased with increasing DP content; they prolonged within the 0-50% replacement range and shortened beyond 50%. The autogenous shrinkage value peaked at 1238 με with 50% DP, then decreased with further DP increase, finally dropping to 932 με at 100% DP replacement. Regarding durability, the chloride ion penetration resistance of UHPC showed a trend of first increasing and then decreasing. The electric flux peaked at 89 C with 75% DP, then decreased to 56 C at 100% DP. Meanwhile, an appropriate amount of DP optimized the particle gradation and improved the pore structure, but excessive DP incorporation led to gradation imbalance and inhibition of the hydration process. Scanning Electron Microscope (SEM) analysis revealed the generation of microcracks, and Thermogravimetric Analysis (TGA) confirmed a decrease in the degree of hydration. Furthermore, completely replacing QP with DP significantly improved the eco-economical performance of UHPC, reducing carbon emissions by 11 kg CO₂/m³, lowering energy consumption by 119.32 MJ/m³, and decreasing material costs by 8.1%. This study provides an important theoretical basis and technical pathway for the green and sustainable development of UHPC.