Despite the fact that the Bayesian network has great advantages in logical reasoning and calculation compared with the other traditional risk analysis methods, there are still obvious shortcomings in the study of dynamic risk. The risk factors of the earth-rock dam breach are complex, which vary with time during the operation period. Static risk analysis, limited to a specific period of time, cannot meet the needs of comprehensive assessment and early warning. By introducing time factors, a dynamic Bayesian network model was established to study the dynamic characteristics of dam-breach probability. Combined with the calculation of the conditional probability of nodes based on the Leaky Noisy-Or gate extended model, the reasoning results of Bayesian networks were modified by updating the data of different time nodes. Taking an earth-rock dam as an example, the results show that it has less possibility to breach and keep stable along the time axis. Moreover, the factors with vulnerability and instability were found effective, which could provide guidance for dam risk management.

To promote the application of recycled concrete in construction engineering, the flexural behavior of ultra-high toughness cement-based composite (UHTCC) materials and recycled concrete composite beams was investigated in this study. Recycled aggregates were used in the production of both recycled UHTCC (R-UHTCC) and recycled concrete. A total of 10 beams were manufactured and tested under four-point bending load. The primary design parameters included concrete strength grade, R-UHTCC layer height, stirrup spacing in the pure bending section, and tensile reinforcement ratio. The effects of these parameters on the failure mode, crack width, load-midspan deflection response, ductility, load-tensile reinforcement strain response, and flexural capacity of the beams are discussed. The results indicate that limiting the use of R-UHTCC to a specific height range within the tensile zone of the beams can yield superior flexural properties compared to using R-UHTCC across the full section. The R-UHTCC and recycled concrete composite beams demonstrated good crack resistance, load-deflection response, and ductility. Compared to the R-UHTCC layer height and stirrup spacing, the influences of concrete strength and tensile reinforcement ratio on the flexural behavior of the composite beams are more significant. The maximum increase in flexural capacity and ductility index was 18.8% and 67.3%, respectively, as the concrete strength grade increased from C30 to C70. The flexural capacity increased by 64.6% as the longitudinal reinforcement ratio increased from 0.258% to 3.68%. Furthermore, a stiffness calculation method based on the effective moment of inertia was proposed and validated through experimental results. The research findings provide a theoretical and design basis for the application of R-UHTCC and recycled concrete composite beams in engineering.

Geopolymer materials represent a novel green cementitious material characterized by excellent mechanical properties and unique microstructural features. This study developed geopolymer mortar using slag as the primary raw material by adjusting alkali content and water glass modulus. Characterization methods, including nanoindentation testing, mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD), were employed to systematically analyze the influence mechanisms of alkali content and water glass modulus on the mechanical properties and microstructure of slag-based geopolymer mortar. Results demonstrated that compressive strength exhibited an initial increase followed by a decline with rising alkali content and water glass modulus, while flowability first increased and then decreased. When the water glass modulus was 1.4, and the alkali content reached 8%, the geopolymer mortar achieved a 28-day compressive strength of 86.5 MPa and flexural strength of 10.2 MPa. At 10% alkali content, flowability reached 240 mm. Compressive strength showed a trend of initial increase followed by a decrease with increasing alkali content, reaching a maximum value of 86.4 MPa at 8% alkali content after 28 days. Nanoindentation analysis revealed that the primary strength-forming phase in geopolymer mortar was C-A-S-H gel. Variations in alkali content and water glass modulus primarily affected the volume fractions of C-A-S-H gel, porous phases, and unreacted slag particles, with limited impact on micromechanical parameters of individual phases. These findings not only provide a theoretical basis for optimizing the mix design of slag-based geopolymer mortar but also offer practical guidance for its application in high-strength and workable construction materials.