Influence of industrial solid waste as filling material on mechanical and microstructural characteristics of cementitious backfills

Abstract

Use of industrial solid wastes (e.g., fly ash, desulfurization gypsum, steel slag) as mine fill material not only solves the environmental risks dictated by the sustainable management of these wastes, but also reduces the operational costs of backfilling. Utilization of backfill in underground mining enhances both local and regional ground support, leading to maximum ore extraction and minimum solid wastes storage. In this study, the mechanical and microstructural characteristics of cementitious backfill (CB) with fly ash-FA, desulfurization gypsum-DG, and steel slag-SS were studied by both uniaxial compressive strength (UCS) and scanning electron microscope test. CB samples were made at a constant solid content of 70 wt% and subjected to UCS testing after a curing time of up to 14 days. Cement-to-solid waste ratio for all CB samples was kept as 1:12. Results reveal that: the UCS value of 14-day cured fills ranges between 1.32 and 2.60 MPa, and the optimal ratio of solid waste was 2:4:4 (DG: FA: SS). The strength performance of backfilling increases with increasing DG and FA values and decreases with increasing SS value. The failure form of backfills is manifested as a tensile failure, and at the bottom of the phenomenon of varying degrees of loose expansion. Microstructural analyses showed that the hydration products in CB samples includes AFt and C-(A)S-H gels. The mineralogical name of AFt is Ettringite (3CaO.Al2O3.3CaSO(4).32H(2)O). The cementing performance of the latter is better than the first (AFt). With the increased FA contents and curing times, hydration products in CB increased and porosity decreased. The outcome of this work will afford a theoretical support for using solid waste as backfilling, advance the management techniques for employing the fill and also propose significant savings in the cement-related costs without negotiating on the safety.