Abstract
The tailings and rice straw are waste by-products, and the storage of tailings on the ground and the burning of rice straws will seriously damage the ecological environment. In this study, the effect of different contents of alkalized rice straw (ARS; rice straw was alkalized with 4% NaOH solution) on the mechanical properties and microstructure of cemented tailings backfill (CTB; ARSCTB) was studied through uniaxial compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The results indicated that 1) the UCS of ARSCTB could be improved by ARS. However, with the increase in the ARS content from 0.1 to 0.4 wt%, the UCS showed a monotonous decreasing trend. The UCS improvement effect was best when the ARS content was 0.1 wt%, and at 7, 14, and 28 days curing ages, the UCS increased rate was 6.0, 8.3, 14.7% respectively. 2) The tensile strength of ARSCTB was generally higher than that of CTB and positively correlated with the ARS content. The tensile strength increase rate was 24.1–34.2% at 28 days curing age. 3) The SEM test indicated that the ARS was wrapped by cement hydration products, which improves its connection with the ARSCTB matrix. ARS performed a bridging role, inhibited cracks propagation, and provided drag or pulling force for the block that is about to fall off. Therefore, the mechanical properties of ARSCTB were enhanced. However, under high ARS content, the inhibition of ARS on hydration reaction and the overlap between ARS were not conducive to the improvement of the UCS of ARSCTB. 4) The post-peak residual strength and integrity effect of ARSCTB were greater. It is recommended to add 0.1–0.2 wt% ARS to the backfill with high compressive strength requirements such as the empty field subsequent filling mining method and the artificial pillar. 0.3–0.4 wt% ARS is incorporated into backfill with high tensile strength requirements such as high-stage filling with lateral exposure and artificial roof. This study further makes up for the blank of the application of plant fiber in the field of mine filling and helps to improve the mechanical properties of backfill through low-cost materials.
Highlights
The mined-out areas formed during the mining of metal mines lead to the movement and fragmentation of rock layers, which in turn causes surface settlement in the mining area, unbalanced ecological environment, and even a series of problems such as safety accidents (Yang et al, 2017; Xu et al, 2019a; Huang et al, 2019; Zeng et al, 2020; Zheng et al, 2021)
When the alkalized rice straw (ARS) content was 0.2, 0.3, 0.4 wt%, it had the same properties, that is, with the increased curing age, the better the improvement effect of ARS on the UCS of ARSCTB; 3) At 7 days curing age, when the ARS content was 0.2, 0.3, 0.4 wt%, the UCS of ARSCTB was reduced by 2.0, 5.0, 6.0% compared with cemented tailings backfill (CTB), and the UCS of other ARSCTBs was higher than the corresponding CTB
When the ARS content is 0.4 wt%, the diffraction peak of hydration products decreases obviously. It indicated that the inhibition effect of ARS on cement hydration reaction is enhanced, which leads to the decrease of adhesive strength between ARS and the ARSCTB matrix, so the UCS of ARSCTB decreases
Summary
The mined-out areas formed during the mining of metal mines lead to the movement and fragmentation of rock layers, which in turn causes surface settlement in the mining area, unbalanced ecological environment, and even a series of problems such as safety accidents (Yang et al, 2017; Xu et al, 2019a; Huang et al, 2019; Zeng et al, 2020; Zheng et al, 2021). With the gradual depletion of shallow mineral resources, mines around the world have become deeper, high ground stress, and rockburst are the key factors leading to goaf instability (Hao et al, 2020). To solve the above problems, cemented tailings backfill (CTB) is widely used in underground mines around the world because of its ability to effectively control ground pressure, reduce surface settlement, and manage tailings (Liu et al, 2016; Wang et al, 2016; Zhao et al, 2017; Cao et al, 2019a; Yang et al, 2020). CTB is a complex composite material produced by mixing tailings (70–80 wt%), cementing materials (3–7 wt%), and a corresponding proportion of water, which is transported to underground stopes by gravity or pumping (Yang et al, 2018; Xue et al, 2019a). It is necessary to seek low-cost and wide-ranging admixtures to improve the mechanical behavior of the backfill
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