Effects of temperatures and pH values on rheological properties of cemented paste backfill

In this study,different influence mechanisms associated with temperatures and pH values were investigated through cemented paste backfill(CPB)systems.CPB samples were prepared with temperatures ranging from 10 to 50℃ in 10℃ increments and pH values of 3,7,and 13.Then,the CPB mixture were subjected to rheological tests,thermogravimetric analysis(TG),derivative thermogravimetry analysis(DTG),Fourier-transform infrared spectroscopy(FT-IR),and scanning electron microscopy(SEM).Results demonstrated that the temperatures had significant effects on the rheological properties of CPB,whereas the effects of pH values were relatively unapparent.Higher temperatures(over 20℃)were prone to bring higher shear stress,yield stress,and apparent viscosity with the same pH value condition.However,an overly high temperature(50℃)cannot raise the apparent viscosity.Non-neutral conditions,for pH values of 3 and 13,could strengthen the shear stress and apparent viscosity at the same temperature.Two different yield stress curves could be discovered by uprising pH values,which also led to apparent viscosity of two various curves under the same temperatures(under 50℃).Microscopically,rheological properties of CPB were affected by temperatures and pH values which enhanced or reduced the cement hydration procedures,rates,products and space structures.

Chemically induced changes in the geotechnical response of cementing paste backfill in shaking table test

Cemented paste backfill(CPB)is extensively used for underground mine support and/or tailings management.However,CPB behavior under cyclic loadings might be affected by the chemistry of its porewater,which often contains sulphate ions.Till today,no studies have addressed the effect of sulphate on the response of CPB to cyclic loadings by using shaking table technique.This study presents new findings of assessing the effect of the sulphate in the pore water of CPB on its geotechnical response to cyclic loading by using shaking table.CPB mixtures were prepared(with and without sulphate),poured into a flexible laminar shear box,cured to 4 h,and then exposed to cyclic loading using one-dimensional(1D)shaking table.Several parameters(e.g.pore water pressure,settlement,lateral deformation,acceleration,electrical conductivity,effective stress,and liquefaction susceptibility)were monitored or determined before,during,and after shaking.Obtained results indicate that the sulphate-bearing CPB cured to 4 h can be prone to liquefaction under the studied conditions.However,sulphate-free CPB samples are resistant to liquefaction.These results are expected to contribute to a better understanding of the effect of water chemistry on the cyclic behavior of CPB,consequently enhancing the cost-effective design of CPB structures.

Experimental investigation on flow properties of cemented paste backfill through L-pipe and loop-pipe tests

With the gradual depletion of available ore at shallow depth,deep mines have been widely operated around the world and therefore need a longer distance to transport the backfill to the underground stope.In this case,the determination of pressure drop is more important in the pipeline transportation system design.As the pilot loop systems require a large amount of capital and manual investment,even its results are reliable,there is an urgent need to find an alternative simple and cost-saving method to determine the pressure drop.Hence,laboratory L-pipe and a pilot-loop tests were employed to study the flow properties of cemented paste backfill cured at various solid and binder content.The results indicate that the L-pipe test presented a similar trend to the loop test,but the L-pipe was characterized by higher pressure drop values for various solid and cement contents.As cement content increased beyond 0%,the paste in the L-pipe showed a slighter difference in pressure drop evolution compared to the paste in the loop-pipe.These results suggest that the simple L-pipe is a workable substitute for semi-industrial loop tests and can provide guidance for designing practical CPB pipeline systems in deep mines.

Experimental study of the shrinkage behavior of cemented paste backfill

Cemented paste backfill(CPB)is largely used in underground mine stopes worldwide.When a CPB is placed in a stope,an important task is to estimate the settlement associated with the shrinkage and selfweight consolidation of the CPB.This is closely related to the volume management to ensure the stability of barricades and tight contacts between the backfill and stope roof.Over the years,shrinkage studies were mostly performed on fine-grained soils(silts and clays),with only a few publications on the shrinkage behavior of uncemented tailings.No study has been published on the shrinkage behavior of CPB.To fill this gap,a series of shrinkage tests has been conducted on CPB with different cement contents,including zero cement content(uncemented paste backfill,uCPB).The results show that the shrinkage response of CPB is very different from that of uCPB.At a given initial water content,CPB exhibits a shorter normal shrinkage stage than uCPB.The unsaturation onset water content and void ratio,shrinkage limit and final void ratio of CPB are generally higher than those of uCPB.At a given cement content,the shrinkage behaviors of CPB and uCPB are significantly influenced by the initial water content.

PVAc添加量对热压法快速固化水泥刨花板性能的影响

以杨木刨花为原料,42.5#普通硅酸盐水泥为无机胶黏剂,Na2SiO3为快速固化添加剂,研究添加聚醋酸乙烯酯乳液胶对热压快固水泥刨花板性能的影响。结果表明:①添加聚醋酸乙烯酯乳液可显著改善板材的物理力学性能;②要保证热压法快速固化水泥刨花板达到较理想的物理力学性能,应将板材在卸压后的回弹率控制在≤10%的范围内。

快速固化水泥刨花板的工艺试验

以速生杉木加工剩余物为主要原料、Na2SiO3为快速固化添加剂制备水泥刨花板,研究了冷、热压两种压板方 式、Na2SiO3添加量、热压温度、热压时间、水灰比、灰木比、水泥种类和刨花形态等因素对水泥刨花板主要性能的影 响。结果表明,热压法可适用于水泥刨花板制造,最佳工艺条件为:Na2SiO3添加量10%、热压温度95℃、热压时间 12min、水灰比0.6、灰木比2.6,制备的水泥刨花板的静曲强度达到10MPa;采用MgCl2后处理能显著改善板的性 能。

减水剂对全尾砂胶结膏体充填材料性能的影响研究

对减水剂对全尾砂胶结膏体充填材料性能的影响进行了研究,采用压汞测孔仪(AutoporeⅣ9500)测定了固化体的总孔隙率和孔径分布。试验结果表明:当料浆坍落度为180mm且水泥掺量分别为3%、5%和7%(以总固体质量计)时,与未掺减水剂相比,掺减水剂能使料浆的固体浓度分别提高4.3%、3.9%和4.1%,能使固化体28d抗压强度分别提高52%、81%和106%。当料浆坍落度为180mm、水泥掺量为5%并且养护龄期为7d、14d和28d时,与未掺减水剂相比,掺减水剂能使固化体抗压强度分别提高46%、90%和81%。结合固化体压汞测孔和抗压强度结果,得出结论:当保持料浆坍落度、水泥掺量和养护龄期相同时,与未掺减水剂相比,掺减水剂能降低固化体的总孔隙率和减小固化体的平均孔径,这可能是减水剂分散了料浆中的水泥和降低了料浆水灰比的复合作用的结果(并且水泥掺量越高或养护龄期越长,复合作用越显著),从而增加了固化体中骨料与骨料之间的黏结程度,因此提高了固化体的抗压强度。

Mill tailings based composites as paste backfill in mines of U-bearing dolomitic limestone ore

This paper elaborates on the development of paste backfill using mill tailings generated during the processing of a uranium ore deposit hosted in dolomitic limestone. The tailings have been characterized in terms of the physical, chemical and mineralogical properties. Time-dependent rheological behaviors and geotechnical properties of cemented paste backfill(CPB) are also determined. The studies show that the mill tailing has the potential to form paste and the CPB has adequate strength to provide support to mine pillars, roofs, and walls.

Stability analysis of shallow tunnels subjected to eccentric loads by a boundary element method

This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.

基于小波神经网络的水泥刨花板弹性模量预测

以机床废料刨花和普通硅酸盐水泥为主要原料,采用热压法生产快速固化制水泥刨花板,研究了灰木比、陈放时间、含水率和密度等对水泥刨花板弹性模量的影响。利用小波神经网络对其弹性模量进行预测。重点讨论了BP神经网络的拓扑结构和学习算法。通过对检验结果进行分析比较,证明了利用小波神经网络能对水泥刨花板弹性模量进行精确的预测。

充填体和围岩-充填体界面剪切特性对比试验研究

拱效应理论模型在剪切力学参数(黏聚力c和内摩擦角j)的选取上采用了等效原则。为了区分剪切参数的选取对拱效应理论模型的影响,首先,采用三轴测试方法,开展常侧向约束条件下围岩-充填体界面的三轴剪切和充填体的三轴压缩试验。基于Mohr-Coulomb强度理论框架,对不同养护时间下充填体和围岩-充填体界面的剪切力学参数进行对比和量化分析。然后,利用电子扫描电镜(SEM)和热差异分析(TG/DTG)的分析手段,充分解释充填体和围岩-充填体界面剪切参数的差异性。最后,依据试验测试结果,对Terzaghi理论模型的工程应用进行讨论。研究表明,随侧向约束的增加,围岩-充填体界面的剪切位移-剪切应力曲线呈现出多峰值现象,且充填体的轴向应变-偏应力曲线呈现出明显的弹性强化阶段。充填体的剪切力学参数(c_(b),φ_(b))要明显大于相应围岩-充填体界面的参数(c_(i),φ_(i))。两者的黏聚力比值(c_(b)/c_(i))相差了2.26~2.67倍,内摩擦角比值(φ_(b)/φ_(i))相差了1.65~2.76倍。且采用围岩-充填体界面的剪切参数(c_(i),φ_(i))进行充填采场竖向应力(σ_(v))的预估能有效地克服Terzaghi理论模型的局限性。研究结论可为充填采场拱效应的预估和数值分析中力学参数的选取提供一定的参考。