The discrete element method (DEM) was used to establish the slump model and J-Ring model of concrete to describe the flow behavior in the slump test and J-Ring test. Then, the contact parameters of particle-particle and particle-geometry for the concrete DEM model, including restitution coefficient, rolling friction coefficient, static friction coefficient, and surface energy, were measured. In order to avoid the influence of the shape and size of the aggregate, this paper used high-precision glass spheres as the aggregate of the concrete for meso-calibration test, slump test, and J-Ring test. Comparing the simulation results of DEM model with slump test result, a very high agreement between the initial stage, the rapid flow stage, and the slow flow stage of the slump flow–time curve can be found as well as the final slump and slump flow. Moreover, similar to the slump DEM model, the DEM models of J-Ring test, V-funnel test, and U-channel test were established to study the passing ability and filling ability of concrete with outstanding accuracy. Therefore, the concrete DEM model with contact parameters and JKR model can be adopted to study the flow behavior of the fresh concrete.

The interface bonding properties of FRP-reinforced concrete under wet/dry conditions are studied by performing the interface bond test. The effects of the number of wet/dry cycles and FRP layers, and FRP reinforcing sequence on the efficiency of reinforcement are studied. The microstructure of FRP-concrete interface is observed by SEM. The variations in bond properties of FRP-concrete interface under extreme conditions under tension are investigated. Experimental results show at the early stage of wet/dry cycles, the strengths of concrete and epoxy resin increase, and further interface bond strength enhances. As wet/dry cycles forward, defects and loose microstructure form in both FRP and concrete, and the interface bond strength decreases. Under identical conditions, the interface bond strength of sample strengthened by FRP after wet-dry cycles is higher than that of sample strengthened before wet-dry cycles. FRP-concrete bond strength is related to the number of wet-dry cycles.