The development of ultra-high-performance fiber-reinforced mortars has prompted extensive research on their performance and structural applications. The development of high-performance fiber-reinforced mortar dates to the 1980s in Europe. A major milestone was achieved around the year 2000 with the commercialization of high-performance fiber-reinforced mortars exhibiting compressive strengths (f’_c) of 180 N/mm², later applied to structural and architectural components. Currently, there is increasing demand for fiber-reinforced mortars with approximately f’_c = 100 N/mm² offering improved economy and constructability, while materials exceeding 300 N/mm² have also emerged. However, comprehensive and rational design guidelines applicable across this diverse range of materials have not yet been established. This study proposes a shear strength evaluation formula for RC/PC beams without stirrups, fabricated using ultra-high-performance fiber-reinforced mortar (UHPFRM) with f’_c values of 100 to 300 N/mm² and 2 vol.% steel fibers. Finite element analyses were conducted to reproduce shear behavior, resulting in the development of an analytical model to predict UHPFRM beam behavior. Parametric analyses evaluating f’_c, span-depth ratio, effective depth, longitudinal reinforcement ratio, and prestress clarified their influence on shear strength. Furthermore, regression analysis of experimentally measured diagonal crack angles yielded an evaluation formula that accounts for longitudinal reinforcement ratio and prestress. Based on these findings, an improved shear-strength evaluation formula was developed and validated against experimental results.

The utilization of industrial solid waste presents a viable approach to supplementing the consumption of natural sand and gravel resources, thereby alleviating resources pressure and reducing environmental burden. Ferrochrome slag (FCS), known for its excellent mechanical properties, has garnered significant interest as a potential substitute for conventional sand and gravel aggregates. To maximize the value of ferrochrome slag, FCS was used as fine aggregate to prepare ultra-high performance concrete (UHPC) with excellent properties in this paper. The effects of aggregate substitution rate and fiber content on the static and dynamic mechanical properties of UHPC were systematically investigated, and the evolution of dynamic damage was further validated through numerical simulation. Moreover, the underlying mechanisms for performance enhancement were elucidated using multiple microstructural characterization techniques. Results indicate that the incorporation of FCS significantly improves both the static and dynamic mechanical properties of UHPC. Microscopic analyses confirm that the addition of FCS reduces porosity and enhances the interfacial bonding between the matrix and the aggregate. This study offers novel insights into aggregate selection for UHPC and provides theoretical and technical support for the application of ferrochrome slag in UHPC.

This study investigates the effect of recycled coarse aggregate (RCA) replacement ratio on the frost resistance of self-compacting concrete (SCC). The experimental program was conducted in Linzhi, Tibet, China, a representative high-altitude region characterized by low atmospheric pressure and cold climatic conditions. SCC mixtures with RCA replacement levels of 0%, 25%, and 50% were prepared and subjected to repeated freeze-thaw cycles (FTCs). The results indicate that increasing RCA content tends to reduce the workability of SCC; however, this effect can be effectively mitigated through the incorporation of polycarboxylate-based superplasticizers. As the RCA replacement ratio increased, the frost resistance of SCC progressively deteriorated, as evidenced by higher mass loss, greater reductions in RDEM, and lower residual compressive strength. After 250 FTCs, the RDEM retention values of SCC-RCA0, SCC-RCA25, and SCC-RCA50 were 77.36%, 71.13%, and 65.39%, respectively, indicating aggravated freeze-thaw deterioration with increasing RCA replacement ratios. Microstructural analyses suggest that higher RCA contents are associated with weaker interfacial transition zones, which may promote damage accumulation and crack propagation under freeze-thaw action. An improved comprehensive evaluation model integrating mechanical performance, material cost, predicted service life, and carbon emissions was proposed to assess the overall performance of the mixtures. The comprehensive performance index is governed by the combined effects of the RCA replacement ratio and the transportation distance. Based on the proposed comprehensive evaluation framework and the conditions considered in this study, SCC incorporating 25% RCA exhibits relatively favorable overall performance when the transportation distance is below approximately 7.4 km; beyond this distance, SCC without RCA becomes the more suitable option. This finding provides practical guidance for selecting RCA replacement levels in SCC for infrastructure construction in such high-altitude cold regions under comparable environmental conditions.