Experimental Study on Microstructure and Erosion Mechanisms of Solid Waste Cemented Paste Backfill under the Combined Action of Dry-Wet Cycles and Sulphate Erosion.

Haowen Xue,Ling Liu,Xilin Li,Chuanyang Du,Qi Sun,Kexin Li

doi:10.3390/ma15041484

Abstract

Solid waste cemented paste backfill (SWCPB) meets the needs of coal mining area management. SWCPB is a cementitious paste backfill material without added cement and is made only from oil shale residue (OSR), steel slag (SS), soda residue (SR) and water. In this study, mine water characteristics were simulated by combining dry–wet cycling experiments with sulphate erosion experiments. SWCPB was assessed regarding appearance, mass loss, and unconfined compressive strength (UCS), and the erosion products were microscopically analysed with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The mechanism for erosion of the SWCPB by sulphate-rich mine water was comprehensively analysed and revealed. Research showed that the erosion mechanism was divided into two parts: chemical and physical erosion. Low concentrations of sodium sulphate promoted hydration, thereby contributing to the increased mass and strength of SWCPB. At high sodium sulphate concentrations, the erosion mainly consumed Ca(OH)2 within the material, and the main generated erosion products were gypsum and ettringite (AFt). This was accompanied by the destructive effects of Na2SO4 crystal expansion, which resulted in damage and the reduced workability of the SWCPB. The whole erosion process was continuous, mainly due to transformations of pits, pores and cracks. The conclusions of this study may provide appropriate guidance for application of SWCPB materials in the treatment of coal mine backfills. In addition, the corresponding theoretical analysis of the erosion mechanism for SWCPB materials is provided.

Highlights

China is very rich in coal resources, and the scale and intensity of current coal mining is at an unprecedented level [1]
Since no cement or chemical reagents were added to the Solid waste cemented paste backfill (SWCPB), it relies on synergistic hydration between the component materials to develop strength
In the course of our research on SWCPB materials, we carried out X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests on the raw materials and the material cured for 28 d in the standard state to analyse the reasons for strength development without the addition of cement and chemicals

Summary

Introduction

China is very rich in coal resources, and the scale and intensity of current coal mining is at an unprecedented level [1]. To effectively protect and utilise resources and reduce ecological pollution, backfilling mining is the best option [2]. The best filling method is cemented paste backfill (CPB). The prepared material meets filling requirements and is inexpensive, with low environmental impact on groundwater. These studies have effectively contributed to the development of SWCPB. Compared to other CPB materials, SWCPB requires no chemical excitation and no cement addition, enabling the 100% application of solid waste. It has the advantages of a wide range of raw materials, low cost and low environmental pollution. It has a wide range of applications and development prospects

Methods

Results

Conclusion