Concrete is a multiphase composite material composed of coarse aggregate, cement mortar, and interface transition zone (ITZ). It is of great significance to study the effect of ITZ and coarse aggregate on chloride microscopic diffusion behavior for predicting the service life of reinforced concrete (RC) structures. By introducing the random distribution function, a random coarse aggregate model considering the randomness of the thickness of the ITZ was established. Furthermore, a two-dimensional (2D) chloride ion diffusion mesoscopic model was developed by specifying different diffusion properties for different phase materials of concrete. Moreover, the effects of coarse aggregate rate, ITZ thickness, and ITZ diffusion property on chloride ion diffusion behavior were investigated in this paper. The research showed that the aggregate has hindrance and agglomeration action on chloride ion diffusion. Although the volume content of the ITZ was very small, less than 0.2% of the total volume of concrete, the effect of the ITZ on the chloride diffusion in concrete cannot be ignored. More importantly, the mechanism of promoting chloride diffusion in the ITZ was revealed through the chloride diffusion trajectory. The research revealed the transmission mechanism of chloride ions in the meso-structure of concrete and provides theoretical support for the design of RC structures in coastal areas.

Human thermal comfort presents noticeable variation across urban and rural areas. Among previous studies, only a few field investigations focus on thermal comfort experienced by rural houses within hot summer and warm winter (HSWW) zones, especially across the north area. The existing thermal environment and energy-saving standards in China make it difficult to provide accurate guidance for building performance design in this area due to the lack of thermal comfort information for humans. This study undertook a field-based survey in rural houses in Hezhou, located in the northern part of an HSWW zone in China. Both on-site environmental data collection and subjective surveys were performed at the same time. Subsequently, this study examined the correlation of operative temperatures with subjects’ perceptions of the thermal environment. Our findings indicate that the actual neutral temperature in summer was 25.34 °C, whereas the predicted value was 25.17 °C. Temperatures within the range of 21.69~30.55 °C were considered acceptable during the operation. The elderly had a higher thermal tolerance than the adults. There was no significant statistical difference between males and females. Our findings contribute to the ongoing development of thermal comfort research for rural housing.

The cracking of recycled aggregate concrete (RAC) is well known to promotes the chloride diffusion, accelerates the corrosion of reinforcement embedded in RAC. To reveal the mechanism of chloride diffusion in RAC under cracking, a multiphase mesoscopic model for chloride diffusion in RAC was proposed. It should be noted that RAC is regarded as eight-phase composite materials consisting of coarse aggregate, reinforcement, new and old mortar, new and old interface transition zones (ITZ), cracks, and damage zones. The effects of the width and depth of cracks and damage zones on chloride diffusion behavior in RAC after cracking were further investigated. The numerical simulation results show that the damage zones accelerate the chloride diffusion and exacerbates the accumulation effect of chloride at the crack tip. Compared to the crack depth, the crack width of RAC has a small effect on chloride diffusion behavior, especially, the crack width is less than 50 µm. More importantly, the chloride diffusion streamline generated by numerical simulation reveals the mechanism of cracks promoting chloride diffusion. The research in this paper provides new insights into the durability design of RAC by revealing the diffusion behavior of chloride ions in RAC.

Ceramsite concrete has gained prominence in sustainable construction and sponge city development owing to its lightweight nature and thermal insulation properties. However, its inherent brittleness and low tensile strength have restricted broader applications. Emerging research highlights fiber reinforcement as an effective enhancement strategy. This study innovatively integrates waste sugarcane bagasse fibers into mortar formulations, conducting comprehensive mechanical tests across varying fiber ratios. Experimental results reveal significant improvements in flexural, compressive, and split tensile strengths with fiber incorporation, with the split tensile strength exhibiting a maximum enhancement of 17.7%. Optimal mechanical performance is achieved at a fiber content of 3% by volume. This study also explores the mechanical performance of bagasse fiber ceramsite concrete (BFRLC) with different bagasse fiber content (0%–6%) at different high temperatures (25–700°C). Under thermal exposure ranging from 25°C to 700°C, the compressive and splitting tensile strength of BFRLC demonstrates an increasing trend with increasing sugarcane fiber content before decreasing, with optimal mechanical performance observed at 4.5 vol% fiber volume fraction. At 500°C, the BFRLC containing 4.5 vol% sugarcane fibers exhibited 10.0% and 39.7% improvements in compressive strength and splitting tensile strength, respectively, compared to standard ceramsite concrete. More significantly, both compressive and splitting tensile strengths of BFRLC exhibit a biphasic degradation pattern under thermal loading, demonstrating gradual deterioration followed by a precipitous decline as temperature escalates, with 500 °C representing the critical thermal transition threshold. Compared to 500°C, at 700°C, the compressive strength of BFRLC is reduced by up to 42.3%, and the split tensile strength of BFRLC is reduced by up to 59.7%. These findings provide quantitative guidelines for optimizing bagasse–ceramsite concrete formulations and processing methodologies, effectively balancing mechanical performance, thermal stability, and environmental sustainability.