Abstract:To reveal the effects of the number of dry-wet cycles and the material density gradient on the deterioration laws of macroscopic mechanical properties, microscopic damage mechanisms, and failure modes of foam concrete, foam concrete test blocks with densities of 800 kg/m3, 1 000 kg/m3, and 1 200 kg/m3 were investigated in this paper. Macro-micro joint tests and three-dimensional discrete element simulation methods were combined. Specifically, 25 dry-wet cycle tests, nuclear magnetic resonance pore analyses, and uniaxial compression tests were conducted, and a discrete element model considering particle expansion and contraction, as well as crystalline salt deterioration effects was constructed. The results indicate that the interface is deteriorated by dry-wet cycles through periodic particle expansion and contraction and crystalline salt precipitation, and the pore connectivity rate is significantly increased; after 25 cycles, the strength loss rates of the FC-800, FC-1 000, and FC-1 200 test blocks are 23.37%, 17.59%, and 13.97%, respectively. The damage mode is regulated by the density gradient; diffused cracks are induced by the low-density zone to weaken the overall bearing capacity, while localized concentrated expansion of cracks is promoted by the high-density zone. The material instability is caused by force chain fractures and displacement field mutations. Based on the differences in damage modes caused by the density effect, a subgrade layered optimization strategy is proposed in this paper: High-density materials are adopted in the surface layer to resist deterioration, and low-density materials are selected in the deep layer to reduce load. A microscopic theoretical basis and operable engineering recommendations are provided by this paper for the long-term service performance of road and bridge transition sections under the dry-wet cycle environment.
