Recycled concrete technology can promote the sustainable development of the construction industry, but the insufficient mechanical properties of recycled concrete have become a key constraint on its development. By adding waste fibers, the mechanical properties of recycled concrete can be improved, and the problem of disposing of waste polypropylene fibers can be solved. In this article, the effects of recycled brick aggregate content and waste fiber content on the mechanical properties and microstructures of recycled brick aggregate concrete through macroscopic mechanical experiments and microstructure experiments are investigated. The results show that the addition of recycled brick aggregate reduces the mechanical properties of concrete; when the content of recycled brick aggregate is 100%, the compressive strength and splitting tensile strength decrease by 22.04 and 20.00%, respectively. The addition of waste fibers can improve the mechanical properties of recycled brick aggregate concrete, but it is necessary to control the contents of waste fibers in a certain range. When the content of waste fibers is 0.08%, the best improvement effect on the mechanical properties of concrete is achieved; the compressive strength of concrete with a 50% (100%) recycled aggregate replacement rate increases by 6.06% (8.90%), while the splitting tensile strength of concrete with a 50% (100%) recycled aggregate replacement rate increases by 2.30% (6.16%). Through microstructural analysis, the mechanism by which waste fiber improves the mechanical properties of recycled brick aggregate concrete is revealed. The addition of waste fibers has the effect of strengthening the framework inside the recycled brick aggregate concrete, forming a good structural stress system and allowing the recycled brick aggregate concrete to continue to bear loads after cracking. In this study, waste brick aggregate and waste fiber are effectively utilized, which can not only reduce pollution to the environment but also realize the sustainable utilization of resources.

In this article, a review focusing on the frost resistance of recycled coarse aggregate concrete (RAC) and the bond performance of RAC with rebar under freeze–thaw environment is carried out. The results show that there are still some controversies about the advantages and disadvantages of the frost resistance of RAC, and many influencing factors have not been considered. The mass of the RAC pullout specimens shows a trend of first increasing and then decreasing after freeze‒thaw cycles. The failure modes of the RAC pullout specimens after freeze‒thaw cycles include pullout failure, pullout-splitting failure, splitting failure, and rebar yielding failure. The bond performance of RAC with rebar shows a degradation trend after freeze‒thaw cycles, mainly in the decrease in bond strength and the increase in bond slip. The bond performance of RAC specimens is inferior to that of natural aggregate concrete specimens after freeze‒thaw cycles. The bond strength prediction models and the bond–slip constitutive relation prediction models of RAC with rebar after freeze‒thaw cycles have been summarized to ensure that engineers can better understand their applicability. The bond stress distribution between the RAC and rebar in the anchoring area is not uniform and constantly changes with the number of freeze‒thaw cycles. The degradation mechanism of the bond performance of RAC with rebar after freeze‒thaw cycles is analyzed.

This study systematically evaluates the influence of the recycled coarse aggregate (RCA) replacement rate and the number of freeze–thaw cycles (FTCs) on the frost damage of recycled aggregate concrete (RAC) through rapid freeze–thaw tests, and delves into the underlying damage mechanisms. The findings demonstrate that the incorporation of recycled aggregates deteriorates the frost resistance of concrete to a certain extent, primarily manifested by increased apparent damage with rising FTC numbers and RCA content. Specimens with an RCA replacement rate exceeding 50% exhibited extensive mortar spalling and aggregate exposure after 50 FTCs. The mass loss rate initially decreased in the early freezing-thawing stage, then began to increase after approximately 20 cycles, reaching a maximum of 5.09%. The relative dynamic elasticity modulus (RDEM) decreased with an increase in both FTCs and RCA content, dropping to a minimum of 71.99%. Furthermore, based on the relative dynamic elastic modulus, this study developed a GM(1, 1) freeze–thaw damage prediction model applicable to a full replacement range of 0%–100% RCA with a precision level of Grade I. Microstructural analysis revealed that microcracks and pores within the interfacial transition zones (ITZs) and the surrounding matrix of both NCA and RCA are critical for the initiation and propagation of freeze–thaw damage, thereby elucidating the damage mechanism in RAC.

The mechanical responses of sandy soil under dynamic loading is closely related to protective engineering and geotechnical engineering, is still not fully understood. To investigate the energy attenuation law and propagation velocity of compressed waves in dry sandy soil, this paper focuses on the dynamic response of compression waves in the specimen under single impact and repetitive impact conditions using an improved split Hopkinson pressure bar (SHPB). The results reveal that the length of the specimen follows an exponential relationship with the attenuation of the peak stress. As the length of the specimen increases from 40 to 240 mm, the attenuation rate of the peak stress increases from 26.3 to 99.0%. The velocity of the peak stress decreases with increasing specimen length, indicating a correlation between these two factors. Furthermore, the impact test results reveal that the number of impacts and the density of the specimen affect the attenuation of the compressed wave. As the number of impacts increases, the density of the specimen also increases, resulting in a gradual decrease in the degree of compressed wave attenuation. When the density increases from 1.60 to 2.29 g/cm³, the attenuation of the compressed wave decreases by 17.0%, and the energy absorption density increases from 0.241 to 1.172 MJ/m³, representing a 386.3% increase. Additionally, the study reveals that the energy absorption efficiency decreases with increasing number of impacts at the same stress level. However, after two impacts, the energy absorption efficiency approaches a steady state. At the same strain level, the energy absorption efficiency remains consistent, indicating the material’s energy absorption characteristics.

This paper presents a typical 450 m high rock slope in a highly jointed and fractured rock mass at Pubugou (PBG) hydropower station on the Dadu River. We established a set of multiphase field geological survey combined with GPS, inclinometers, and piezometer monitoring system to analyze the deformation and failure mechanism of rock slope. The results show that small-scale excavation in road construction disrupted the balance of the Pubugou rock slope (PBGRS), and several local retrogressive failures occurred at the toe. Monitoring data regarding surface and subsurface movements show that the PBGRS is stable as a whole. The deformation concentrated mainly in the loosened fractured zone, which was a feature with sliding-compression cracking. Highly loosened rock mass was the predominant factor affecting the stability of the PBGRS, while the role of reservoir water level fluctuation, though positive, was not significant. Overall, the PBGRS still has a high potential for further development, especially in the slope’s upper zone. To reinforce the slope, measurements mainly consist of the concrete frame combined with anchor cables constructed on the slope. In this study, the analysis was carried out of pre- and postreinforcement measure slope stability with numerical simulation, and safety factor increased from 1.09 to 1.21. This study’s findings have important implications to the analytical method and reinforcement design with geological settings like that of the PBGRS.