Strength and deformation properties of polypropylene fiber-reinforced cemented tailings backfill
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摘要: 針對膠結充填體脆性強、易開裂等問題，以聚丙烯纖維為加筋材料，通過設置水泥與尾砂質量比為1∶10和1∶20，纖維摻量為0、0.05%、0.15%和0.25%的充填體進行無側限抗壓強度試驗，探究纖維摻量對膠結充填體強度及變形特性的影響，借助掃描電鏡（SEM），從微觀角度探討纖維對充填體力學性質的作用機制。研究結果表明：充填料漿的屈服應力隨纖維摻量增加呈線性增大，其流態模型符合Bingham流體；隨著纖維摻量的增加，充填體的無側限抗壓強度呈先增大后減小趨勢，纖維最優摻量為0.15%；摻入纖維有效地減緩了裂紋的擴展，約束了充填體的變形，充填體的峰后應變軟化延長，殘余強度增大，破壞特征由脆性向延性轉變；纖維的加固效果主要受纖維與尾砂?水泥基體界面之間的黏結與摩擦作用控制。Abstract: Cemented tailings backfill (CTB) technology, an innovative mode of tailings management, has been widely applied in many metal mines worldwide due to its advantages of safety, environmental protection, and high economic benefit. During the mining process, CTB should have sufficient mechanical strength to maintain the stability of the underground stopes and provide a safe environment for workers and mining equipment. However, in deep mining, cracks and imperfection in CTB are usually generated by the extraction of adjacent stopes, blasting disturbances, and stress concentration. Existence of these cracks weakens the engineering properties. It causes instability of backfill stopes and increases ore dilution. At present, the mechanical strength of CTB structures is improved by increasing binder content, which directly leads to an increased backfilling cost. Hence, to solve the problems mentioned above, CTB specimens were prepared with cement-tailings ratios of 1∶10 and 1∶20, and polypropylene fiber contents of 0, 0.05%, 0.15%, and 0.25% (by dry weight of tailings and cement). The effect of fiber content on the mechanical strength and deformation properties were investigated by conducting unconfined compressive strength (UCS) tests. Referring to scanning electron microscopy (SEM), the mechanism of fiber reinforcement is discussed. Results indicate that the yield stress of fresh CTB mixtures increase linearly with increasing fiber content, and the rheological characteristic of the mixtures conformed to the behavior of Bingham. UCS values of CTB increase with increasing fiber content, but decrease when the fiber content is > 0.15%. Optimal fiber content is 0.15%. It is found that fibers can effectively delay the expansion of cracks and constrain the deformation of backfill. The post-peak strain softening and residual strength are improved by the addition of fibers. Failure characteristics of CTB are transformed from brittleness to ductility due to the mixed fibers. The reinforcement effect of fiber is mainly controlled by the adhesion and friction between fibers and tailings-cement matrix. The overall objectives are to improve current understanding of the mechanical properties of CTB, thereby reducing the risk of clogged pipelines and higher backfilling costs as well as improving the stability of CTB structures.
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圖 2 料漿屈服應力隨纖維摻量變化關系
Figure 2. Relationship between yield stress and viscosity coefficient of slurry with fiber content
圖 3 充填體試件應力?應變關系曲線. (a) 養護齡期3 d; (b) 養護齡期7 d; (c) 養護齡期28 d
Figure 3. Stress?strain curves of CTB specimens: (a) curing age of 3 d; (b) curing age of 7 d; (c) curing age of 28 d
圖 4 充填體抗壓強度與纖維摻量的關系. (a) 養護齡期3 d; (b) 養護齡期7 d; (c) 養護齡期28 d
Figure 4. Relationship between UCS of CTB and fiber content: (a) curing age of 3 d; (b) curing age of 7 d; (c) curing age of 28 d
圖 7 纖維與尾砂?水泥基體界面力學作用示意圖
Figure 7. Schematic diagram of mechanical interaction between fiber and tailings?cement matrix
圖 10 充填體試件破壞方式. (a) 纖維摻量0; (b) 纖維摻量0.05%; (c) 纖維摻量0.15%; (d) 纖維摻量0.25%
Figure 10. Failure modes of CTB specimens: (a) fiber contents of 0; (b) fiber contents of 0.05%; (c) fiber contents of 0.15%; (d) fiber contents of 0.25%
表 1 尾砂和水泥的化學組成成分
Table 1. Chemical composition of tailings and cement
材料 化學成分質量分數/% SiO2 CaO Fe2O3 Al2O3 MnO K2O MgO CuO SO3 Na2O TiO2 燒失量 尾砂 52.60 11.60 17.20 3.68 0.11 2.43 4.56 0.19 0 4.87 1.75 1.01 水泥 20.34 64.78 3.11 5.02 0 0.35 1.09 0 2.20 0.10 0.26 2.75 
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表 2 聚丙烯纖維的物理力學參數
Table 2. Physical and mechanical parameters of polypropylene fiber
類型 長度/mm 直徑/μm 密度/（g·m?3） 抗拉強度/MPa 彈性模量/GPa 延伸率/% 耐酸堿性 分散性 束狀單絲 12 31 0.91 ≥400 ≥3.5 30 極強 極好
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表 3 料漿流變特性參數
Table 3. Rheological property parameters of the slurry
灰砂比 纖維摻量/% 擬合方程 n 相關系數，R2 1∶10 0.00 τ=65.84+1.22γ 1.00 0.9908 1∶10 0.05 τ=83.49+1.57γ 1.00 0.9921 1∶10 0.15 τ=107.46+1.84γ 1.00 0.9894 1∶10 0.25 τ=136.60+2.61γ 1.00 0.9893 1∶20 0.00 τ=63.98+1.07γ 1.00 0.9830 1∶20 0.05 τ=78.45+1.50γ 1.00 0.9920 1∶20 0.15 τ=103.59+1.93γ 1.00 0.9917 1∶20 0.25 τ=130.08+2.27γ 1.00 0.9876
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表 4 不同纖維摻量下充填體試件脆性程度指標
Table 4. Brittleness index of CTB specimens under different fiber contents
灰砂比 纖維摻量/% △σ ${\upsilon _\sigma }$ Bs 1∶10 0.00 0.93 0.2959 0.2752 1∶10 0.05 0.83 0.2479 0.2058 1∶10 0.15 0.81 0.2434 0.1972 1∶10 0.25 0.71 0.2172 0.1542 1∶20 0.00 0.86 0.2704 0.2325 1∶20 0.05 0.78 0.2243 0.1750 1∶20 0.15 0.67 0.2041 0.1367 1∶20 0.25 0.66 0.1971 0.1301
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