In recent years, with the acceleration of urbanization and the continuous expansion of construction at all scales, the safety, durability, and sustainability of building structures have come to face multiple challenges

The corrosion of alkaline concrete materials exposed to a sulfuric acid environment is becoming more and more prevalent, and its damage assessment is becoming more and more imperative. This study aims to describe the corroded surfaces of concrete with different strength grades (C30, C50, C80) in sulfuric acid environments in terms of their three-dimensional fractal dimension. Three kinds of concrete with varying strength grades, namely C30, C50, and C80, were immersed in a sulfuric acid solution with pH ≈ 0.85 for four distinct corrosion durations, specifically 0, 28, 56, and 165 days, in accelerated corrosion tests. The 3D laser scanning technique was utilized to capture the 3D coordinates of the surface points of the concrete cylinder before and after corrosion. The fractal dimension of concrete’s uneven surface before and after corrosion was computed via the cube covering method, and the mass loss of the concrete specimen was also obtained. The outcomes demonstrate that the three-dimensional fractal dimension provides a new method for characterizing the degree of corrosion deterioration of concrete samples affected by sulfuric acid via laser scanning technology. From the perspective of the appearance, mass loss, and fractal dimension of a rough surface in the sulfuric acid environment at a pH level of approximately 0.85, the degree of the corrosion deterioration of concrete is ranked from high to low as C80 > C50 > C30. These fractal dimensions of the concrete’s corroded surfaces with various strength grades increase rapidly in the initial period. However, as the corrosion time progresses, the growth rate of the corroded surface fractal dimension gradually decelerates and tends towards stability, which accords with the law of exponential function. The widespread belief is that the higher the strength grade of concrete, the better its durability; however, this pattern varies in sulfuric acid corrosive environments. Therefore, based on this research, it is recommended that in extremely acidic environments (i.e., very low pH), more attention should be paid to high-strength grades of concrete.

Prefabricated Ultra-High-Performance Concrete (UHPC) and cast-in-place Normal Concrete (NC) composite members are increasingly used in bridge engineering because they combine high performance with cost-effectiveness. The bond at the UHPC-NC interface is critical as it directly impacts the composite structure’s safety. This study employed 3D laser scanning acquired the UHPC substrate geometry, utilized fractal dimension analysis to quantify the interface roughness, and adopted the slant shear test to evaluate the effects of retarder application mass and hydration delay duration on roughness and bond strength. The research results indicate that the failure modes of UHPC-NC specimens can be categorized into interface shear failure and NC splitting tensile failure. With the extension of hydration delay duration, both the interface roughness and bond strength show a decreasing trend. The influence of retarder dosage on interface roughness and bond strength exhibits a threshold effect. This study also confirms the effectiveness of fractal dimension as a quantitative tool for characterizing the macroscopic roughness features of the bonding interface. The findings of this paper provide a solid theoretical basis and quantitative support for optimizing key process parameters such as retarder dosage and precisely controlling hydration delay duration, offering significant engineering guidance for enhancing the interface bonding performance of UHPC-NC composite structures.

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant.

Compared with polyvinyl alcohol-engineered cementitious composites (PVA-ECC), engineered cementitious composites containing polyethylene fibers (PE-ECC) has captured the attention of researchers because of lower cost. Nevertheless, there is a limited amount of research that focuses on their dynamic behavior. Thus, specimens with different water binder ratios were tested by split Hopkinson pressure bar (SHPB) to unveil the dynamic compressive behavior of PE-ECC. The dynamic behaviors were analyzed based on the tests, including dynamic failure modes, dynamic stress-strain curves, dynamic compressive strength, dynamic peak strain, and dynamic toughness. The result shows the PE-ECC has excellent compressive ductility, and a long post-peak descending part in the stress-strain relations. Furthermore, the sensitivity analysis reveals that the strain rate is the most crucial factor that directly affects the dynamic compressive strength, dynamic peak strain, and dynamic toughness in a monotonic fashion.