A new type of prestressed composite recycled aggregate floor slab was developed and its flexural performance was studied. The composite floor comprises a top cast-in-place slab made of recycled coarse aggregate concrete and a bottom precast concrete slab with grouted steel tube trusses. The cracking load, ultimate load, deflection, steel tube strain, concrete strain and failure process are studied for different contents of recycled coarse aggregates. Results show that the mechanical performance of the prestressed composite recycled aggregate slab has two distinctive stages. And the load bearing capacity decreases with the increase in the amount of recycled coarse aggregates. When the composite slab fails, the prestressed steel wires in the tension zone yield and concrete in the compression zone is crushed. This failure characteristic reflects that the reinforcement ratio of the component is appropriate. The cracking moment and ultimate moment calculation formulas of the composite slab are established and could predict the cracking and failure points. In the formulas, the influence of the amount of recycled coarse aggregates on the flexural capacity is considered. By controlling the content of recycled aggregates, the composite slabs with steel tube trusses can be sued in practical applications.

In order to address a challenging issue in the recycling of construction debris, the impact of carbonization treatment on the characteristics of recycled aggregates (RCAs) was experimentally examined in this work. Both direct carbonization and carbonization following calcium hydroxide pretreatment were used in the study to assess the impact of carbonization on the physical characteristics of recycled aggregates. According to the findings, carbonization raised the recycled aggregates’ apparent density while drastically lowering their porosity and water absorption (by as much as 20–30%). Although the recycled aggregate’s crushing index marginally increased with age, its overall physical qualities remained excellent. Pretreatment with calcium hydroxide can improve the physical characteristics of recycled aggregates, further optimize their pore structure, and efficiently encourage the carbonation process. Furthermore, recycled aggregate’s crushing index can be considerably decreased and its quality much enhanced by the ultrasonic cavitation treatment. According to the study, the carbonation-treated recycled aggregate’s microstructure was denser in the interfacial transition zone and had a stronger link with the cement paste, improving the recycled aggregate concrete’s overall performance. XRD, infrared spectral analysis, and SEM scanning were used to determine the increased calcium carbonate content in the recycled aggregate following carbonation treatment as well as its microstructure improvement process. The findings offer fresh concepts for achieving resource efficiency and environmental preservation through the use of recycled aggregates in concrete, as well as theoretical backing for their use.

In order to investigate the static and cyclic tension behavior of post-installed rebar along with cement-based adhesive that is adopted after exposure to high temperature, a three-phase experimental program has been carried out and two typical embedment depths, 10d and 15d are designed. The surfaces of specimens are firstly heated up to 800°C, and then the residual strength at different temperatures of cement-based adhesive has been studied by consequent static pull-out tests. Experimental results show that the tensile strength has a significant reduction at elevated temperatures compared with that of room temperature. The cement-based adhesive has almost lost its full bond strength when the temperature exceeds 350°C. Finally, the bond performance of cement-based adhesive under cyclic loading has been further tested and analyzed. It is found that both 10d and 15d specimens have failed abruptly with rebar pull-out. The employment of long embedment depth has been verified to be an effective method to improve the bond performance of cement-based adhesive under static and cyclic loading. Static numerical investigation indicates that the bond stress distribution is not uniform along the embedment length of post-installed rebar at different temperatures of cement-based adhesive. The temperature-dependent tensile strength prediction has also been obtained based on the experimental data.

ABAQUS software was first used to study the structure behaviour of steel-to-concrete connection by post-installed anchorage under cyclic loading. Three types of embedment depth 25d, 20d and 15d were considered. Based on previous simulation results of earthquake and fire, it can be concluded that the seismic performance of steel-to-concrete connection by post-installed anchorage is strongly related to the rotation angle 0 of steel beam. The heat analysis results indicate that the fire resistance of post-installed connection after 2 hours exposure could meet the requirement of related codes. Based on the simulation results mentioned above, a performance-based design conception with four performance levels has been provided to guarantee structure safety under the combined action of earthquake and fire. According to the principle of performance-based methodology, rotation angle 0 of steel beam and fire resistance rating T are chosen as critical index for performance evaluation. Among the 4 levels of performance, Level 1 has the highest specification for disaster protection. To achieve the performance level 1, the thickness of fire protection layer should not be less than 45 mm, and the embedment depth should be 25d at least.

Structural displacement monitoring faces significant challenges under complex environmental conditions due to the loss or degradation of target features, making it difficult for traditional methods to ensure high accuracy and robustness. Therefore, this study proposes a structural displacement identification and quantification method that integrates YOLOv8n with an improved edge-orientation gradient-based template matching algorithm. By combining deep learning techniques with traditional template matching methods, the accuracy and robustness of monitoring are enhanced under adverse conditions such as noise and extremely low illumination. Specifically, in the edge-orientation gradient matching stage, the Canny-Devernay sub-pixel edge detection technique and an improved ellipse-fitting method are employed for sub-pixel edge extraction, and a five-level Gaussian pyramid structure is introduced to accelerate the matching speed. Experimental results show that the proposed method achieves high-precision displacement monitoring under sufficient illumination, and it maintains stable target localization and displacement quantification performance under conditions of noise interference and extremely low illumination. Notably, under salt-and-pepper noise interference, although YOLOv8n maintains a high level of localization confidence, the accuracy of gradient matching deteriorates, resulting in a root-mean-square error (RMSE) of 0.035 mm. This finding reveals the differential impact of various noise types on different stages of the algorithm. The proposed method offers a novel technological approach for precise structural displacement monitoring in complex environments.