Determination of fracture parameters and prediction of failure mode for solid waste concrete incorporating recycled rubber and PET

Solid waste concrete (SWC) incorporating recycled rubber and polyethylene terephthalate (PET) exhibits a complex fracture response because crack propagation is jointly governed by heterogeneous aggregate-matrix interfaces and specimen size effects. However, existing fracture models rarely account for the coupled influence of multi-source aggregate structures. This study proposed a meso-fracture analysis model for SWC by linking the fictitious crack growth at peak load to the particle size, content, and interfacial characteristics of natural, PET, and rubber aggregates within the framework of boundary effect model. The proposed model enables the simultaneous determination of size-independent fracture parameters ( f t & K IC ), achieving remarkable accuracy with relative errors of only 6.64% - 27.72% for f t and 1.03% - 14.87% for K IC compared to the size effect model (SEM). All experimental results fall within the quasi-brittle fracture regime and are bounded by the proposed ±30% fracture-failure prediction curves. Furthermore, discrete element method (DEM) mesoscopic numerical simulations of three-point bending tests were performed to establish a simplified two-point approach based on the equivalent crack-length ratio, a e-ratio = a e-max / a e-min . The results indicate that a e-ratio ＞4 provides a rational criterion for simultaneously determining f t and K IC . At a e-ratio = 8, the two-point estimates differ from the multiple-point fitting results by only 0–8.7% for K IC and 2.27–19.96% for f t . The proposed framework provides an efficient route for determining size-independent fracture parameters and predicting the failure behavior of SWC containing multi-source recycled aggregates. This study offers essential technical support for the safe design and crack stability evaluation of SWC structures, providing a solid scientific foundation for solid waste resource utilization and low-carbon building materials development.