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In order to investigate the effects of fly ash and steel fiber on the abrasion resistance of ultra-high performance concrete (UHPC), this paper performed macroscopic mechanical test, underwater abrasion resistance test and microscopic characterization such as SEM and MIP to investigate the effects of fly ash and steel fiber on the workability, mechanical properties, microstructure, and abrasion resistance of UHPC. The results show that the replacement of cement by fly ash delays the emergence of hydration peak by about 3 h, and the cumulative heat flow at 3 d is reduced by 18%, significantly improving the workability of UHPC. The incorporation of fly ash reduces the mechanical properties of UHPC in the early stage and has no effect on the mechanical properties in the later stage. The incorporation of steel fiber improves the flexural strength and compressive strength of UHPC. The flexural strength and compressive strength are increased by 82% and 47% respectively due to the composite mixing of steel fiber and fly ash under steam curing. The addition of fly ash has little effect on the abrasion resistance of UHPC, while the addition of steel fiber improves the abrasion resistance of UHPC, and the composite mixing of steel fiber and fly ash increases the abrasion resistance of UHPC by 58%. The compressive strength and abrasion resistance strength of UHPC show a significant positive correlation. The incorporation of fly ash reduces the most available pore size, porosity and capillary pore content, making the internal structure of matrix more uniform and denser. [ABSTRACT FROM AUTHOR]

Carbonation is a critical factor contributing to the degradation of reinforced concrete systems. Understanding the micro-mechanism of concrete carbonation is essential for mitigating corrosion losses. This study investigates the transport and reaction processes of water and CO2 in CSH pores with varying calcium–silica ratios using reactive force field molecular dynamics. Simulation results reveal that CO2 and its hydration products occupy adsorption sites on the CSH, hindering solution transport within the pores. As the Ca/Si ratio increases, the adsorption of Ca ions on the CSH matrix weakens, facilitating Ca's reaction with CO2 and its displacement from the CSH surface. Consequently, a wider distribution of Ca on the surface occurs, and CO2 directly adsorbs onto the CSH matrix, widening the transport space and accelerating transport speed. Furthermore, the impact of bridging silica–oxygen on the CSH surface is analyzed, indicating that the absence of bridging silica–oxygen enhances adsorption sites for Ca ions, thus intensifying their adsorption on CSH. [ABSTRACT FROM AUTHOR]

The proposal of sintered sludge cement (SSC) paste aligns with the low-carbon development goals of building materials. However, there is a lack of scientific guidance for the preparation of sintered sludge ash (SSA). Herein, this study systematically investigates the influence mechanism of mechanical–thermal activation parameters of SSA on the mechanical properties and life cycle assessment (LCA) of SSC paste, and conducts a comprehensive evaluation using a radar chart and the TOPSIS method. The results show that with the increase in calcination temperature and duration, the compressive and flexural strengths of the SSC paste are improved, especially at 600 °C and above, increasing by 57.92% and 62.52%, respectively. The longer calcination time at 1000 °C results in a decrease in its mechanical properties. The addition of SSA significantly reduces the LCA indicators of cement paste. Specifically, 30% SSA only contributes 8.1% to the global warming potential. Compared to calcination, the LCA indicators have less sensitivity to ball milling, and prolonging the time hardly increases them. Based on performance and environmental impact, the optimal SSA is obtained by calcining at 800 °C for 2 h and ball milling for 10 min. This study can provide theoretical guidance for efficient building material utilization of dredged sludge. [ABSTRACT FROM AUTHOR]

Using fly ash (FA) to modify magnesium phosphate cement (MPC) not only extends setting time and enhances MPC performance but also reduces costs. Currently, high‐quality FA is predominantly used, whereas the accumulation of low‐quality FA poses challenges for waste management and environmental protection. This study focuses on low‐quality FA with excessive sulfur content. Initially, X‐ray fluorescence spectroscopy was employed to select two types of FA with SO3 contents of 1.06% and 6.07%. FA replaced magnesium oxide in equal mass to prepare FA/MPC composite cementitious materials. The composite materials were studied for hydration heat, phase composition, infrared spectroscopy, mechanical properties, and microscopic morphology to explore SO3's impact on MPC hydration processes, microstructure, and properties. The findings indicate that adding FA effectively dilutes reactants, extending setting time from 7 to 17 min and 18 min, aiding construction operations. In the FA/MPC composite cementitious materials, MPC hydration, along with FA's synergistic hydration, forms a new hydration product MgSiO3, improving material density and mechanical strength post‐hardening. Excessive SO3 in high‐sulfur FA accelerates MgO decomposition, providing ample Mg2+ for K‐struvite synthesis, promoting MPC hydration, and transforming K‐struvite from amorphous to crystalline, enhancing material strength. [ABSTRACT FROM AUTHOR]