To realize resource utilization of solid waste and improve the performance of recycled concrete blocks in severe cold regions of the Qinghai-Tibet Plateau, this study investigates the effects of recycled fine aggregates and active supplementary cementitious materials on the impermeability, water resistance and frost resistance of loadbearing concrete blocks, based on 100% replacement of coarse aggregates with recycled aggregates. The microstructure of recycled concrete was analyzed by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). A life cycle assessment (LCA) approach was employed to quantitatively evaluate material performance, costs and carbon emissions. The results show that the permeability and water absorption of load-bearing recycled concrete blocks increase with the increase of the proportion of recycled fine aggregates, while they decrease first and then increase with a reduction in the fly ash-to-slag blend ratio. Conversely, frost resistance and the softening coefficient exhibit the opposite trend. Under the condition of 100% recycled coarse aggregate replacement and a fly ashto-slag blend ratio of 3∶1, the compressive strength of the blocks reached 11.77 MPa, flexural strength was 3.89 MPa, softening coefficient was 0.99, water absorption was 0.7%, mass loss after 50 freeze-thaw cycles was 2.2%, and the loss rates of compressive and flexural strength were 10.2% and 13.9%, respectively. These properties meet the load-bearing and durability requirements for severe cold regions, making this mix ratio the recommended formulation. Microscopic analysis shows that alkali activation promotes secondary hydration in the composite cementitious materials, generating additional hydration products that fill internal pores, thereby enhancing the densification of the recycled concrete. However, with the increasing freeze-thaw cycles, the number of internal pores gradually increases, with micropores and mesopores envolving into macropores and cracks, leading to performance degradation.Based on the performance-cost-carbon emission analysis, using 100% recycled coarse aggregates alone is unfavorable for carbon reduction. In contrast, the recommended mix proportion incorporating both recycled aggregates and active SCMs demonstrates the optimal comprehensive benefits, achieving a carbon reduction rate of 31.03%.

Cushion materials can effectively reduce the impact load acting on the rigid protective structures such as shed tunnel and improve the impact resistance of the structures. In order to investigate the variation of cushioning performance of recycled concrete aggregate (RCA) under successive impacts, drop weight impact tests and discrete element simulations are carried out. Test results show that compared with the quartz sand cushion, the transmitted load at the center of concrete shed for RCA under the first impact reduces by 83%, and it is distributed more uniformly. With the increase in the number of impacts, the cushioning performances of both the RCA and quartz sand deteriorate. For the sixth impact, the maximum transmitted loads at the center of concrete shed for RCA and quartz sand are 11.2 times and 1.4 times those of the first impact, respectively. Furthermore, the cushioning performance is strongly influenced by particle shape. The numerical simulation results show that when the proportion of strip particles increases from 0% to 100%, the rotation angle and translation distance of the particles decrease by 40% and 20%, respectively, and the maximum drop weight impact load increases by 37%. The inter-locking effect between particles increases with the irregularity of particle shape, which limits the rotation and translation of the particles, and increases the drop weight impact load and the transmitted load on the concrete slab. The research results may provide theoretical basis and engineering guidance for RCA as a new type of eco-friendly cushion.

Based on the energy equilibrium, the computational formula of critical buckling length of multi-layer rock slope is derived. Considering interlayer and cross joints, the numerical manifold method is used to simulate the buckling evolution process of Malvern hills slope in New Zealand, and the theoretical calculation and numerical simulation results are compared with the field measured data. The results show that numerical manifold method can accurately simulate slope buckling failure process by preforming interlayer and cross joints. The process of slope buckling deformation and instability failure can be divided into interlayer dislocation-slight bending, slope toe traction-sharp uplift and accelerated sliding-landslide formation. Under the long-term action of self-weight, the evolution of slope buckling from formation to failure mainly includes three stages: initial bending, sharp bending and landslide formation. The angle between cross joint and slope normal is defined as β. Among the four kinds of cross joints with the angle β of 0°, 15°, 30° and 45°, the slope with 45° cross joint is most prone to slipping and bending deformation, the degree of buckling is the largest, and the number of time steps of slipping and bending is the least. When β is in the range of 30°−45°, the numerical simulation results are in good agreement with the reality.