Fracture behaviors of steam-cured concrete and self-compacting concrete under three-point bending:laboratory testing and DEM simulation

• Steam −curd concrete (SC) can better resist crack propagation and play a load-bearing role • Self-compacting concrete (SCC) has stronger deformation capability. • The crack propagation path, force chains, and load-bearing capacity of SC and SCC were observed through simulation. The mechanical responses of concrete are vital for the long-term stability of CRTS III slab track structure. This study employs laboratory tests and discrete element method (DEM) simulations to investigate the fracture behavior and crack propagation of steam-cured concrete (SC) and self-compacting concrete (SCC) used in CRTS III slab tracks. Results reveal that SC primarily fails due to aggregate penetration, while SCC is characterized by aggregate pullout. SC exhibits approximately 28% higher initial fracture toughness, about 30% greater unstable fracture toughness, and nearly 16% higher fracture energy than SCC, along with a modest 3% increase in ductility index. In contrast, SCC shows larger ultimate deformation, a more uniform crack-opening displacement distribution, and a slower evolution of the fracture process zone (FPZ), indicating better deformation capacity and crack dispersion. DEM simulations show that SC has a straighter crack propagation path, denser force-chain networks, and higher load-bearing capacity due to continuous stress transmission through the mortar matrix. Conversely, SCC demonstrates significant stress localization within aggregates, resulting in a more tortuous load-transfer path and a complex fracture process.