Study on the modeling method of three-dimensional mesoscopic numerical model of fiber-reinforced recycled aggregate concrete

To better study the mesoscopic mechanical behavior of fiber-reinforced recycled aggregate concrete, an efficient modeling method of three-dimensional mesoscopic numerical model is proposed. For mesoscopic composition, based on the traditional concrete structure of "aggregate-ITZ-mortar", recycled aggregate is further subdivided into "aggregate core-old ITZ-old mortar" to accurately characterize its heterogeneous nature. For random placement of aggregates and fibers, corresponding random placement methods are established according to their respective geometric characteristics. This ensures uniform and random distribution of aggregates and fibers in three-dimensional space. For mesh generation and property assignment of the concrete matrix, a mapping rule based on geometric inclusion relationships is established. It efficiently assigns complex mesoscopic component properties to homogeneous background mesh elements, solving the problem of property allocation for multiphase materials. Subsequently, a corresponding numerical model is established with reference to real specimens in physical tests, and uniaxial compression simulation is carried out. It is found that under the same load conditions as physical tests, the failure mode and stress-strain curve of the numerical model established by this method are largely consistent with the actual situation. Finally, the influence of recycled aggregate replacement ratio on the compressive performance of specimens is studied through numerical simulation. The results show that with the increase of recycled aggregate replacement ratio, the compressive strength of specimens decreases continuously. The main reason is that the weak old ITZ and old mortar of recycled aggregate undergo severe plastic damage during loading. After adding 1% steel fibers to the specimens, their strength and ductility increase compared with before, but the strength still decreases with the increase of recycled aggregate replacement ratio. This method can lay a foundation for subsequent simulations of the mechanical properties of recycled concrete structural components.