Study on the evolution of mechanical properties of backfill body under the combined action of sulfate erosion and load

• Published in: Case Studies in Construction Materials 2024-12, Vol.21, p.e03977, Article e03977
• Main Authors: Zhang, Shengtang, Chen, Shurong, Min, Lingran, Liu, Yin, Rui, Hongru, Zhang, He
• Format: Article
• Language: English
• Subjects: Backfill body; Load; Mechanical properties; Microstructure; Sulfate attack
• ISSN: 2214-5095; 2214-5095
• DOI: 10.1016/j.cscm.2024.e03977

In addition to the complex and varied compressive stress of overlying strata, the backfill body will also be subjected to chemical corrosion of harmful ions in mine water, resulting in the deterioration of the performance of the backfill material, which will lead to the destabilization of the backfill body, affecting the effect of the backfill body. Therefore, to explore the mechanical properties of the backfill under the coupling effect of sulfate concentration and load, the optimal conditions are proposed. Based on the response surface method (RSM-CCD), the effects of sulfate concentration (3 %, 6 %, 9 %) coupled with load level (40 %, 60 %, 80 %) on the mechanical properties of backfill body were studied using macroscopic uniaxial compressive strength test, microscopic scanning electron microscopy (SEM) test and X-ray diffraction (XRD). The results show that the compressive strength of backfill body can be effectively enhanced with appropriate sulfate concentration and appropriate load. With the increase of single-factor sulfate concentration, the compressive strength of backfill increased by 13 %, 39 % and 45 %, and then decreased by 36 %, 37 % and 42 %, respectively. With the increase in load level, the compressive strength firstly increases by 18 %, 20 % and 21 %, and then decreases by 28 %, 32 % and 34 %, respectively. Under the coupling action of sulfate attack and load, sulfate has a great influence on the uniaxial compressive strength of the backfill body in the early and middle stages of the test, and the load has a great influence in the late stage of the test. Under the coupling action of sulfate, the formation of hydrated calcium silicate gel (C-S-H) from tricalcium silicate (C3S) is promoted, the hydration reaction is accelerated, the expansion products of ettringite (AFt) and gypsum are increased, and the compressive strength of the backfill body is reduced. At the same time, the torsional, tensile and shear effects of the coupled loads will also accelerate the deterioration of the backfill body. The experimental data of this study will provide a reference for the design of backfill body in structural backfill, and provide theoretical guidance for improving the durability of backfill paste in coal mines in the future.