聚丙烯纤维加筋固化尾砂强度及变形特性

Strength and deformation properties of polypropylene fiber-reinforced cemented tailings backfill

针对胶结充填体脆性强、易开裂等问题,以聚丙烯纤维为加筋材料,通过设置水泥与尾砂质量比为1∶10和1∶20,纤维掺量为0、0.05%、0.15%和0.25%的充填体进行无侧限抗压强度试验,探究纤维掺量对胶结充填体强度及变形特性的影响,借助扫描电镜(SEM),从微观角度探讨纤维对充填体力学性质的作用机制.研究结果表明:充填料浆的屈服应力随纤维掺量增加呈线性增大,其流态模型符合Bingham流体;随着纤维掺量的增加,充填体的无侧限抗压强度呈先增大后减小趋势,纤维最优掺量为0.15%;掺入纤维有效地减缓了裂纹的扩展,约束了充填体的变形,充填体的峰后应变软化延长,残余强度增大,破坏特征由脆性向延性转变;纤维的加固效果主要受纤维与尾砂−水泥基体界面之间的黏结与摩擦作用控制.

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.