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The fracture process of dried concrete under splitting tensile loading was investigated using a three-phase mesoscale rigid-body spring model (RBSM). Although many studies have reported changes in the splitting tensile strength (f t) owing to drying, the mechanism remains unclear. The f t values under different drying conditions were predicted using a mesoscale concrete model that accounted for the drying-induced mechanical property change (DMPC) of mortar and microcracking. This result supports the assumption that DMPC and microcracking predominantly affect the strength under long-term drying. An investigation of the fracture behavior showed that drying-induced microcracking degraded f t by uniformly reducing the load-bearing capacity of the mortar. However, the cracks also had a slightly positive effect on f t by spreading the fracture area near the peak load, but this benefit was outweighed by the negative effect of cracking at 80 % RH or more intense drying conditions. • Microcrack-evaluation is a key to predicting tensile strength (ft) after drying. • Drying-induced microcracking is key for predicting the change in f t. • Considering creep behavior influenced an 8% change of calculated f t. [ABSTRACT FROM AUTHOR]

The confining effect of concrete cover and stirrups reduces the rate of bond deterioration due to corrosion. However, the large dispersion in recorded experimental data makes it difficult to clearly separate the influence of cover depth and stirrup confinement on bond degradation. This study utilises the discrete 3D Rigid Body Spring Model (RBSM) to conduct a meso-scale investigation regarding the effect of cover thickness and stirrup confinement on internal crack evolution and pull-out behaviour in corroded reinforced concrete models. The simulation scheme is divided into two stages. In stage 1, different degrees of corrosion are introduced, producing cracking in the cover concrete; in stage 2, the corroded main reinforcement is pulled out from the damaged concrete. 3D RBSM is advantageous because the concrete is randomly meshed to reduce mesh bias on crack propagation and the actual geometry of the deformed bars is modelled. The simulation results clarify that the presence of thicker cover delays crack initiation but increases the rate of crack opening. Stirrups do not have any significant effect on crack initiation but effectively restrict crack growth. An investigation of the internal stress in the simulation models shows that tensile stresses generated in stirrups during corrosion are responsible for reactionary confining pressure that restricts crack propagation. Load-displacement curves show reductions in pull-out capacity, stiffness and ductility with increasing corrosion damage. The relative influence of crack opening and stirrup volume on the rate of bond degradation with respect to average surface crack width are discussed and compared with published experimental results and an empirical equation. [ABSTRACT FROM AUTHOR]

Internal stresses induced by the alkali silica reaction (ASR) and delayed ettringite formation (DEF) can cause cracking and degrade the mechanical properties of concrete, but the relationship between these phenomena remains unclear. In this study, crack patterns and the loss of compressive strength and elastic modulus of concrete after ASR and DEF expansion are simulated at the mesoscale using a three-dimensional Rigid Body Spring Model (3D RBSM). Concrete expansions induced by ASR and DEF are introduced in the model by applying initial strain on the springs of interfacial transition zone (ITZ) and mortar elements as damage history respectively. After verifying the model with single aggregate, further analysis of differences in concrete cracking due to ASR and DEF damage is carried out. The effect of the percentage of reactive aggregate is studied in the cases of ASR damage, while different intensified expansion areas are considered in the case of DEF. The simulated losses of mechanical properties of the concrete are compared with the experimental results and good agreement is obtained. It is found that the loss of mechanical properties is dominated by internal cracks rather than the surface crack pattern. Compressive strength is highly dependent on the development of large cracks while elastic modulus is closely related to the total number of cracked faces. More importantly, regardless of the intensified expansion area, the mechanical properties are consistent with expansive cracking damage. [ABSTRACT FROM AUTHOR]