Study on the mechanical properties and failure mechanism of polypropylene fiber–rubber-modified solid waste-based backfill

Abstract

This study focuses on the resourceification of solid wastes. Using NaOH as an activator, limestone powder (LP), slag powder (SP), and fly ash (FA) in a ratio of 24%:28%:48% were combined with spontaneous combustion coal gangue (CG) as the fine aggregate, and tire rubber particles (GTR) and polypropylene fibers (PP) were co-added to prepare new backfill materials for goafs (LSFC + Gs) and (LSFCP + Gs). The mechanical properties of the backfill materials were thoroughly investigated through uniaxial compressive strength (UCS), three-point bending, and splitting tests. The energy evolution of the fillers was analyzed, and digital speckle technology was utilized to precisely assess the damage evolution and failure mechanism of the samples under load. Furthermore, combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM–EDS), the strength formation mechanism was studied. The results indicate that: (1) With the increase of GTR content, the mechanical properties of the backfill materials initially increase and then decrease, with LSFC + G10 and LSFCP + G15 combinations exhibiting the best performance. (2) After the addition of GTR, the total energy and elastic strain energy accumulation of the material increase, correlating positively with UCS. (3) During the compaction and crack generation stages, the horizontal and vertical displacements of the specimen’s transition from initial uniform distribution to non-uniform and discontinuous distribution, and the shear displacement also exhibit similar characteristics. As the displacement difference increases, the specimens show significant deformation characteristics. (4) Under alkaline conditions, LP, SP, and FA produce a large amount of honeycomb-like topological network C–(A)–S–H polymer products, filling the voids within the matrix and thereby enhancing the mechanical properties of the samples. The synergistic effect of the three-dimensional network structure of PP and GTR improves the load-bearing capacity of the samples. The research provides a theoretical basis for the treatment of waste tires and the development of new backfill materials for mining areas.

Graphical abstract