In this paper, an overview focusing on the bond behavior of recycled coarse aggregate concrete (RAC) with steel bar is carried out. The results show that the failure modes of RAC specimen were not only influenced by a single factor, it is necessary to comprehensively consider the influence of various factors on the failure modes of RAC specimen; The steel bar diameter, the concrete cover to diameter ratio and the replacement rate of RCA all affect the load-slip curve of RAC specimen; Bond strength predictive equations and bond-slip relationship models of RAC with steel bar has been summarized to ensure engineers to better understand their applicability; The influencing factors of the bond behavior of RAC specimens including the replacement rate of RCA, the concrete compressive strength, the steel bar type and steel bar diameter, the steel bar embedment length and the aggregate performance; The freeze-thaw cycles and the steel bar corrosion all affect the bond behavior of RAC with steel bar. When freeze-thaw damage and steel bars corrosion reach a certain degree, the bond behavior of RAC with steel bar deteriorates.

The use of geopolymer as a cementitious material for geopolymer concrete (GPC) is beneficial for the sustainable development and green transformation of the construction industry. Geopolymer concrete has many advantages, such as high strength, heat and corrosion resistance, low hydration heat, and carbon emissions. This paper adopted the water–binder ratio, alkaline activator modulus, and slag replacement as the influencing factors, and used the 28-day compressive strength and flexural strength of geopolymer concrete as the response values to seek a reasonable mix design. In addition, through microstructure analysis, the mechanism of geopolymer on concrete was studied. The results indicated that as the water–binder ratio increased, the compressive strength first increased and then decreased, while the flexural strength continuously decreased. As the amount of slag replacement increased, the compressive strength and flexural strength would also increase. The effect of alkaline activator modulus on compressive strength and flexural strength was not significant. Through response surface methodology (RSM) analysis, the optimal design of geopolymer concrete was determined to have a water–cement ratio of 3.50, a modulus of 1.54 for alkaline activator solution, and a slag substitution rate of 47%. The microstructure analysis showed that the water–binder ratio and slag replacement improved the pore structure and density of concrete, thereby enhancing the macroscopic mechanical properties of concrete. This paper can provide a theoretical basis for the application of geopolymer concrete in engineering.