Fracture mechanism of filling layer self-compacting concrete before and after polymer repair in CRTS-III track slabs

The post-poured filling layer self-compacting concrete (FLSCC) in the China Railway Track System-III (CRTS-III) may be subjected to fractures under high-speed train loads. These fractures would seriously affect the operation of track systems and need to be repaired timely. However, the performance improvement mechanisms and the fracture characteristics of polymer-repaired FLSCC have rarely been studied. Thus, this study focused on investigating the fracture characteristics of FLSCC specimens before and after repairing using acoustic emission (AE) and scanning electron microscope (SEM) techniques through three-point bending (TPB) tests. The results indicated that the carrying capacity and ductility of the specimens were improved by 1.2 and 1.4 times after repair, respectively. Both types of specimens ultimately failed due to the FLSCC fracture, with distinct failure mechanisms. For instance, the specimen toughness doubled after repair based on the calculated fracture parameters. The critical crack extension rate of the repaired specimens was 3 times higher than that of the original ones. Consequently, the AE events detected in the repaired specimens were twice as large as those in the original ones. Meanwhile, the repaired specimens produced a large magnitude of b-value fluctuations and released more AE energy with increasing loads. Additionally, the penetrating, bonding, coating and filling effects of the repair polymer observed by micro-analysis improved the fracture performance by interlocking structures. A Mode-I fracture model considering repairing effects was proposed and validated. The results could provide better retrofitting suggestions for the operation and maintenance of CRTS-III.