The high carbon emission of concrete is mainly related to the large amount of cement used in concrete, and the use of bulk solid waste to prepare green high-performance concrete provides a new development path for the realization of the goal of "double carbon". Steel slag and blast furnace slag were used to replace part of the cement as cementitious material, and carbon fiber was used as a reinforcing material to prepare 3D printed fiber-reinforced steel slag cementitious material, and its rheological and mechanical properties were tested, and SEM, low-field NMR, and X-CT were used to analyze the influence of the fibers on the toughening of its mechanical properties. The results showed that with the increase of carbon fiber doping, the dynamic and static yield stresses and plastic viscosity increased, and the thixotropic index, thixotropic ring area and viscosity recovery rate peaked and then decreased when the carbon fiber doping increased to 0.4%. The flexural, compressive and splitting strengths increased with increasing carbon fiber doping. Compared with cast specimens, 3D printed specimens showed anisotropy, specifically compressive strength X direction > Y direction > Z direction, flexural strength Y direction > Z direction > X direction, and splitting strength Z direction > X direction > Y direction. Using SEM, LF-NMF and X-CT methods, it was learned that the carbon fibers were directionally distributed and well dispersed in the 3D-printed materials, and the carbon fiber incorporation effectively reduced the porosity of the 3D-printed specimens and significantly improved the mechanical properties.

The study explored the use of plastic waste in construction materials to address the global increase in plastic waste. Post-consumer and post-industrial plastics high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polyethylene terephthalate (PETE) were processed and combined with fine and coarse aggregates to create polymer composite construction materials (PCCM). Essential physical properties like compressive strength, flexural strength, and split tensile strength were assessed. HDPE composites consistently demonstrated superior mechanical properties, especially with fine aggregate. Microstructural analyses using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) revealed that composites containing nano-plastics possess a compact and uniform structure, enhancing their durability and strength. Incorporating nano-plastics led to a notable 25% increase in compressive strength compared to control samples. In conclusion, integrating demolition waste into construction composites offers sustainable solutions to enhance performance and address plastic waste management challenges in construction.

Sustainability is of ever-increasing importance in the construction industry, and self-healing concrete offers a promising solution to the issue of cracking in concrete. By incorporating crystalline admixtures into a concrete mix, the efficiency of self-healing can be improved in a non-invasive and non-destructive way. In this review, key findings have been compiled from several studies that tested or discussed the effectiveness of self-healing with crystalline admixtures. The review show that it is necessary to first analyse the chemical composition of the raw materials as they have a direct influence on healing efficiency. In addition, at least five analysis methods should be implemented when determining self-healing efficiency, with special emphasis on internal crack-healing efficiency, which can be measured effectively by a technique such as X-Ray tomography. While crack sealing is now considered more critical than mechanical properties, strength retention remains an important property in ensuring the durability of the concrete. Based on this review, this study suggests a general experimental procedure to be followed when conducting self-healing tests with concrete containing crystalline admixture and proposes specific methods for conclusive research work.

Thermal anti-cracking safety evaluation is the foundation of the thermal cracking control. In this study, to overcome the limitations of traditional anti-cracking design methods, a method for determining the whole spatio-temporal real anti-cracking safety of dams is proposed. Dynamic analysis of anti-cracking safety in the whole process is carried out through key process curves of six factors, including concrete temperature, autogenous volume deformation, tensile strength, structural stress, structural allowable stress, and anti-cracking safety coefficient. Based on the theoretical development of dam concrete thermal anti-cracking control, the spatio-temporal temperature gradient control theory and the customized intelligent temperature control strategy for the whole construction process of concrete dams are formulated. The developed evaluation method was implemented in constructing the concrete dams of Xiluodu, Wudongde, and Baihetan. As such, the highest temperature in concrete was controllable, the temperature change was adjustable, and the temperature control measures were optimizable. Thermal cracking was not observed in the post-construction investigation. The results can provide a reference for the design and construction of similar projects.

Reclaimed asphalt pavement (RAP) is a sustainable alternative to natural aggregates, addressing material shortages in construction and promoting eco-friendly practices. In this study, the effect of partial replacement of the RAP in roller compacted concrete (RCC) is investigated, whereas the mechanical properties of obtained concrete mixtures are quantified. The obtained RCC mixes are modified by partial replacement of 10% of cement with silica fume (SF) and an addition of 2% steel fiber (St.F) of the total mix as a reinforcement resulting in improvement of the mechanical properties of RCC. Replacement of natural aggregate (NA) by 100%, 70%, 50%, and 30% of RAP are tested for the altered RCC mix. A total of 129-cylinder RCC samples are prepared and evaluated for mechanical and physical properties for the obtained RCC mixes. The samples were evaluated for compressive strength, tensile splitting strength, the modulus of elasticity, the toughness, the water absorption, and the density. The results showed an increasing trend in compressive strength, and modulus of elasticity, and modulus of toughness with increasing RAP percentages. Contrarily, the RCC density and water absorption were reduced by increasing RAP percentage. While the tensile splitting test results did not show a clear trend by altering the RAP percentages. The obtained compressive strength (20.53 MPa) for 100% RAP is still a reasonable value for pavement with light traffic, sidewalks, or similar constructions using RCC mixes. The study showed that the RAP is recommended for potential utilization of numerous known waste materials in the RCC construction.