Experimental Study on the Mechanical Properties of Rice Husk-Reinforced Eco-Friendly Mine Backfill Material

This study developed an eco-friendly mine backfill material using coal gangue, fly ash, desert sand, and natural rice husk. The mechanical properties and damage evolution characteristics were investigated through uniaxial compression, Brazilian splitting, acoustic emission (AE), digital image correlation (DIC), and scanning electron microscopy (SEM) tests. Polyvinyl alcohol (PVA) fibers provided the highest reinforcement efficiency, followed by polypropylene (PP) fibers. At a natural rice husk dosage of 5%, the backfill reached a compressive strength of 5.6 MPa and a splitting tensile strength of 0.376 MPa, representing an 83.4% increase in tensile strength compared with the fiber-free group and approaching the performance of the PP fiber group. Increasing the cement replacement ratio from 50% to 70% reduced strength, whereas longer curing improved strength development. The coupled AE-DIC observations indicate that natural rice husk incorporation delayed crack localization and changed the failure process from sudden brittle cracking to more progressive damage. SEM observations show that natural rice husk formed local contact and partial embedding with the cementitious matrix, with hydration products around the rice husk and visible pull-out voids. Overall, natural rice husk can be used as a low-cost and sustainable reinforcing material for coal gangue-desert sand-fly ash-based mine backfill.