Five recycled coarse aggregate (RCA) treatment techniques including flow-through carbonation, pressurized carbonation, wet carbonation, nano silica (NS) pre-spraying and combined pressurized carbonation with NS pre-spraying, were utilized to improve the performance of recycled aggregate concrete (RAC). The characteristics of the stress–strain curves of RACs including peak stress, peak strain, elastic modulus, ultimate strain and toughness were evaluated after using the above RCA treatment techniques. A theoretical model for natural aggregate concrete was used to analyse the stress–strain curve of RAC. Additionally, the carbonation resistance of RAC after using different RCA treatment techniques were investigated. The results showed that the calculated stress–strain curve of RAC based on the theoretical model matched well with the experimental results. Among the three types of carbonation techniques, pressurized carbonation caused the highest improvement in peak stress and elastic modulus of RAC, followed by flow-through carbonation, the last was wet carbonation. The NS pre-spraying method contributed to even higher improvement in peak stress and elastic modulus of RAC than the pressurized carbonation method. The combined pressurized carbonation with NS pre-spraying exhibited the highest enhancement of RAC because both the RCA and the new interface transition zone (ITZ) were improved. The carbonation resistance of RAC was improved after using all the studied RCA treatment techniques.

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.

Three-dimensional concrete printing technology provides the possibility to fabricate specific and eco-friendly concrete components for application on shorelines or in other areas, providing environmental protection. In this study, solid wastes in Hong Kong are employed for low-pH 3D printing concrete to further decrease the impact on the environment. The results indicate that WGP replacement in a classic low-pH recipe leads to lower yield stress and surface pH, as well as volume stability. The employment of slag improves workability and printability, but maintains the surface pH and drying shrinkage. The printing height is not merely determined by slump flow, and contributions from every binder on the surface pH are quantified based on simplified calculations. Reducing OPC and increasing SF in the classic low-pH recipe achieves the best printing performance and improved environmental friendliness.

As 3D printing emerges as a transformative technology in construction, the structural performance of 3D-printed mortar (3DPM) has become a key research focus. This study conducted shear tests on reinforced specimens combining 3D-printed mortar (3DPM) and normal mortar (NM). Four different shapes of interfacial locking design (I-shaped, K-shaped, C-shaped, S-shaped) were examined, comparing reinforced (CR) and non-reinforced (NR) specimens. The investigation analyzed failure modes, crack propagation patterns, and shear transfer mechanisms at CR series specimens under direct shear loading. CR-S specimens exhibited a shear peak load value 14.0% higher than CR-K specimens, 33.2% higher than CR-C specimens, and 42.9% higher than CR-I specimens. CR-I specimens exhibited pure adhesive failure. CR-K, CR-C, and CR-S specimens showed composite failure patterns combining adhesive and shear failure mechanisms. Strain analysis revealed the maximum horizontal strain ε_xx across all specimen shapes. CR-C and CR-S specimens recorded strain values exceeding CR-I and CR-K specimens by over 50%. Reinforcement produced pronounced increases in ultimate bearing capacity for I-shaped and C-shaped specimens, achieving gains of 51.9% and 60.4%, respectively. Reinforcement substantially enhanced energy dissipation capacity. Compared with NR series specimens, the performance improvements ranked as follows: CR-C (+164.67%) > CR-S (+70.70%) > CR-I (+52.05%) > CR-K (+9.42%).

The global construction industry contributes to nearly half of total anthropogenic CO₂ emissions, among which building material production accounts for a dominant share