The performance indicators of concrete are mainly determined by the interface characteristics between cement hydration slurry and aggregates. In this study, molecular dynamics technology was used to evaluate the effect of the interfacial water content on the evolution of the interface structure, interaction energy, and mechanical properties of calcium silicate hydrate (C-S-H) and silicon dioxide (SiO₂) systems, and the weakening mechanism of the C-S-H/SiO₂ interface in a humid environment was revealed. The results showed that all stress–strain curves of C-S-H/SiO₂ were divided into the elastic stage and the failure stage. As the interfacial water layer thickened, the molecular weight of the water invading the C-S-H gradually increased, and the desorption of Ca²⁺ ions in the surface region became significant, while the amount of Ca²⁺ ions entering the water-layer region increased. The interaction energy of the C-S-H/SiO₂ progressively became larger, and the energy ratio (ER) significantly decreased; the tensile strength σc and residual strength σr of C-S-H/SiO₂ both showed a downward trend. In summary, a lower water content had a limited impact on the interfacial bonding strength, while the weakening effect enhanced with an increase in the interfacial water content. This phenomenon was also demonstrated in concrete interfacial bond strength experiments.

Before the rock in engineering projects such as mining, tunnel excavation, steep road construction, and oil and gas extraction undergoes failure, macroscopic and microscopic cracks will appear. The management or utilization of these cracks is inseparable from the application of crack detection technology. Some of these cracks are located below the rock surface and have a certain depth, which hinders the application of standard techniques. Therefore, based on the microwave resonance vibration model and using a low-power microwave source along with an enhanced transmission voltage amplitude, this paper proposes a microwave resonance detection method for the depth of hidden rock cracks. Experimental verification was conducted on cement mortar material samples and granite material samples with different preset internal crack depths. The propagation and reflection characteristics of cement mortar and granite material samples were analyzed, and the detection range of hidden crack depth was assessed. The results show that using this method, both cement mortar and granite samples have real-time detection capabilities at the central frequency of 3.667 GHz microwave magnetic field. The method has a fast response speed, and the relative error of the measurement results is within ± 5%. The theoretical maximum penetration depth for cement mortar material samples is 83–263 mm, and for granite material samples, it is 8311–83,107 mm. By comparing the actual test results of the cement mortar samples with the theoretical prediction results, it is evident that the microwave resonance crack depth detection device detected a maximum depth of 82 mm, which is consistent with the calculated range. The aforementioned method provides a new means for the detection of cracks below the rock surface.

The design of intersecting nodes in high-rise oblique mesh structures is a critical issue. The existing research on the intersecting nodes of oblique meshes mainly focuses on plane intersecting nodes and monotonic axial compression loads. The plane intersecting nodes cannot consider the contribution of the node’s out-of-plane angle and floor beam to the node’s out-of-plane stiffness in actual structures. In this paper, numerical analysis using ABAQUS was conducted to investigate the mechanical performance of space intersecting nodes of oblique meshes (OMSIN) under cyclic axial tension and compression loads, to provide a reference for the engineering application of oblique mesh structures in seismic regions. Six parameters were considered: the space intersecting angle, the plane angle symmetry coefficient, the plane intersecting angle, the out-of-plane constraint restraint, the steel content of the cross-section, and the concrete strength. The study showed that changes in the thickness of the steel tube wall are unfavourable for the uniform transmission of stress. Increasing the space intersecting angle significantly weakened the seismic performance, and the space angle affects the failure mode of the node. Asymmetric arrangements of the upper and lower plane angles caused nonlinear development of out-of-plane. The ultimate load and overall compressive stiffness of the specimen were positively correlated with the plane angle, and vertical constraints should be applied to the node position of components with plane angles greater than or equal to 70°. The out-of-plane constraint was a key factor affecting the seismic performance of the node, and it was proportional to the ultimate load of the component. In structural design, if the aim is to improve the mechanical performance of the component by increasing the steel content, more enormous out-of-plane constraints should be set to control plane external displacement strictly. The concrete strength is proportional to the ultimate axial load and axial stiffness, and its influence on the mechanical performance in the axial tension direction is not significant. Finally, a dimensionless skeleton curve model of the node was established. The existing formula for the bearing capacity of CFST columns was fitted to obtain the calculation formula for the axial yield and ultimate load of the OMSIN under cyclic loads.

Under compressive loading, rocks emit electromagnetic waves, and monitoring electromagnetic signals has become a key means of predicting dynamic rock disasters. To understand how dynamic potential is generated in rocks under compressive loading, the relationship between the compressive loading (P) and the stimulated potential (E) is seen as a circuit system (H(t)). A circuit analysis model has been established to study how rock particles restructure under compressive loading. Experimental tests were conducted to measure the input excitation (E) and output response (U_σ(t)) or (I_σ(t)) of the rock specimens, with four types of rocks being tested. The experiments revealed that voltage, current, frequency, and impedance changed during the particle reorganization process under compressive loading, showing that the electromagnetic radiation of the rock specimens mainly came from the current generated by the internal particle reorganization. The intensity of electromagnetic radiation was found to depend on the load size and dynamic impedance (Z_σ), with the dynamic impedance (Z_σ) consisting of the microelement total resistance (R_σ), capacitance (C_σ), and inductance (L_σ). The variation of dynamic impedance (Z_σ) is related to the rock type. The research findings have contributed to elucidating the mechanism of electromagnetic radiation generated by rocks under load.