胶结充填体强度预测及水泥消耗量反演计算

为降低充填成本和使料浆制备系统可靠运转,基于特大型采空区充填工程对于二步骤矿柱开采的重要性,采用配比优化试验及统计分析所得的充填体长期强度预测模型,结合现场充填体地质钻探取样的检测强度,利用预测模型的变形公式,反算出采空区充填水泥实际用量,对设计与实际水泥用量的定量关系进行了分析,掌握了二者之间的偏差.结果表明:前期充填中水泥用量存在较大富余,52-8#和52-10#采场水泥用量分别偏大约60.28%,49.24%.随着充填站操作人员技术水平与熟练程度的提高,并通过对站内计量仪表和物料输送设备校验后,水泥用量的下调空间较大.     

Performance of cemented coal gangue backfill

Possibility of cemented gangue backfill was studied with gangue of Suncun Coal Mine, Xinwen Coal Group, Shandong, and fly ash of nearby thermal power plant, in order to treat enormous coal gangue on a large scale and to recovery safety coal pillars. The results indicate that coal gangue is not an ideal aggregate for pipeline gravity flow backfill, but such disadvantages of gangue as bad fluidity and serious pipe wear can be overcome by addition of fly ash. It is approved that quality indexes such as strength and dewatering ratio and piping feature of slurry can satisfy requirement of cemented backfill if mass ratio of cement to fly ash to gangue is 1：4：15 and mass fraction of solid materials reaches 72%-75%. Harden mechanism suggests that the cemented gangue fill has a higher middle and long term comprehensive strength.     

尾砂胶结充填体与岩体耦合作用机理研究

充填法开采被广泛应用于隐患资源2次开采中,研究充填体与岩体耦合作用机理,对充分利用矿产资源、保护地表建筑物、延长矿山服务年限等方面具有十分积极的作用.以程潮铁矿西区选厂下遗留矿柱2次开采为研究背景,通过对尾砂胶结充填体的无侧限单轴抗压正交力学试验,得到了不同灰砂比、不同浓度、不同龄期参数与充填体单轴抗压强度的曲线关系和多参数线性回归方程式,同时分析了影响充填体抗压强度的主次因素.最终依据充填体与岩体能量匹配原则,通过数值模拟并充分考虑回采中爆破震动对采场稳定性的影响,得出最优充填方案.     

High strain rate compressive strength behavior of cemented paste backfill using split Hopkinson pressure bar

The stability of cemented paste backfill(CPB) is threatened by dynamic disturbance, but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose. Therefore, a split Hopkinson pressure bar(SHPB) was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4, 0.8, and 1.2 MPa. And the failure modes were determined by macro and micro analysis. CPB with different cement-to-tailings ratios, solid mass concentrations, and curing ages was prepared to conduct the SHPB test. The results showed that increasing the cement content, tailings content, and curing age can improve the dynamic compressive strength and elastic modulus. Under an impact load, a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading. And the dynamic compressive strength of CPB has an exponential correlation with the strain rate. The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading. The local damage was enhanced, and fine cracks were formed in the interior of the CPB. This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.     

Correlative mechanism of hydraulic-mechanical property in cemented paste backfill

Hydraulic characteristic is a good indication of binder hydration, which determines the strength development of cemented paste backfill (CPB). Therefore, the hydraulic characteristic should be communicated with the mechanical property to provide an advanced knowledge that can help mine workers make a rational strategy and reduce the mining cycle. An experimental program was performed to obtain the hydraulic (monitored by suction and volumetric water content) and mechanical properties (unconfined compressive strength (UCS) test) of CPB at the 28 days curing age. According to the monitoring and testing results, the relationships between the hydration reaction rate and volumetric water content (VWC), suction and VWC, suction and UCS were established. The hydration degree showed a liner rise as the VWC decreased. Curves of the VWC and UCS were featured with a nonlinear reduction and nonlinear growth (both are exponential functions) as the suction rising, respectively. These established relationships validated the strong correlative mechanism of hydraulic and mechanics behavior for CPB. Also, the results of the present research indicated that the hydraulic characteristics and mechanical property were strongly coupled. These correlations and couplings will be of great importance to understand the hardening process of CPB and bring to a safe CPB field operation.     

Resistivity and thermal infrared precursors associated with cemented backfill mass

The stability of cemented backfill mass is important to keep miners and equipment safe in underground backfill miming.The stress-strain behavior, resistivity and thermal infrared(TIR) characteristics of backfill mass under uniaxial compression were investigated. The monitoring system consisted of a TIR observation system, a stress-strain monitoring system and a resistivity measurement system. Precursory information for impending failure of cemented backfill mass was collected, including TIR, strain and resistivity precursors. The sensitivity and difference of different monitoring information to the same failure event were compared.The results show that the time-space evolution process of the resistivity and TIR is basically the same as the whole process from compression deformation to failure of backfill mass, and the time variation of resistivity and TIR is obviously characterized by stage.The resistivity precursor turns out earlier than the TIR and the strain. The resistivity relation with loading compression is anti-symmetry, decreasing as the compression stress increases before the peak strength of backfill mass. However, when the backfill mass enters into the phase of failure, the resistivity starts to increase as the stress increases. The change of the resistivity growth direction can be regarded as the resistivity-caution-point for the failure of backfill mass under uniaxial compression. It is also indicated that the TIR information mainly represents the surface temperature evolution in the process of compression before the backfill enters into the plastic-yield state. It can be a valuable tool to obtain the precursors for failure of cemented backfill mass for backfill mines.     

Horizontal roof gap of backfill hydraulic support

For the backfill hydraulic support as the key equipment for achieving integration of backfilling and coal mining simultaneously in the practical process, its characteristics will directly influence the backfill body's compression ratio. Horizontal roof gap, as a key parameter of backfilling characteristics, may impact the backfilling effect from the aspects of control of roof subsidence in advance, support stress, backfilling process and the support design. Firstly, the reason why horizontal roof gap exists was analyzed and its definition, causes and connotation were introduced, then adopting the Pro/E 3D simulation software, three typical 3D entity models of backfill hydraulic supports were built, based on the influence of horizontal roof gap on backfilling effect, and influence rules of four factors, i.e. support height, suspension height, suspension angle and tamping angle, were emphatically analyzed on horizontal roof gap. The results indicate that, the four factors all have significant impacts on horizontal roof gap, but show differences in influence trend and degree, showing negative linear correlation, positive linear correlation, positive semi-parabolic correlation and negative semi-parabolic correlation, respectively. Four legs type is the most adaptive to the four factors, while six legs(II) type has the poorest adaptability, and the horizontal roof gap is small under large support height, small suspension height, small suspension angle and large tamping angle situation. By means of optimizing structure components and their positional relation and suspension height of backfill scrape conveyor in the process of support design and through controlling working face deployment, roof subsidence in advance, mining height and backfilling during engineering application, the horizontal roof gap is optimized. The research results can be served as theoretical basis for support design and guidance for backfill support to have better performance in backfilling.     

胶结充填体应变率与声发射特征响应规律

应变率是影响胶结充填体力学特性和声发射特征的重要因素.为研究胶结充填体应变率与声发射特征响应规律,文中进行了单轴压缩条件下胶结充填体的声发射试验,研究了应变率、声发射在加载过程中的时序特征,探讨了应变率与声发射时序特征之间的相关性,以及两者变化趋势之间的内在联系,进一步揭示了荷载作用下胶结充填体的裂纹演化规律.结果表明:胶结充填体应变率、振铃计数率在变形全过程均表现出"升→降→稳→升"的变化趋势和阶段性特征,两者相关性较高;胶结充填体内部破裂是由骨料之间的摩擦以及胶结材料的断裂演化造成,应变率对声发射特征在一定程度上起到了支配作用;基于应变率在塑性屈服和失稳破坏阶段表现出明显的突变性,可为胶结充填体破裂预测提供有效的前兆信息;结合声发射振铃计数率、平静期以及扩容现象可更加全面的反映胶结充填体破裂情况.研究结果可为胶结充填体力学特性研究奠定理论基础.     

Effect of low temperature on hydration performance of the complex binder of silica fume-portland cement

By analyzing the mechanical properties, composition of hydrates, content of Ca(OH)2 and microstructure of the complex binder of silica fume-Portland cement, which cured at constant low temperatures (+5--10 ℃), the effect of different low temperatures on hydration performance of the complex binder at the age of 3, 7 days and 14 days was researched. Experimental results show that hydration processes of the complex binder can be restricted by low temperature. Reducing the curing temperature could cause compressive strength and flexural strength of the complex binder to decrease significantly. The gradient difference between strength diminishes, content of Ca(OH)2 in hydrates reduces, and compactness of the microstructure weakens. Therefore mixing with silica fume can modify various performance indicators of the complex blinder, but reducing the curing temperature restricts the pozzolanic activity of silicon fume.     

掺矿粉水泥的水化机理研究

研究利用在硅酸盐水泥中掺加矿粉来提高水泥的抗折强度,降低脆性,并通过ＴＧ－ＤＴＡ、Ｘ－衍射及ＳＥＭ等微观分析方法对掺矿粉水泥的水化机理进行研究,结果表明,矿粉的掺入不权可以提高水泥的水化程度,增加水泥石的密实度,同时也可以降低水泥石的脆性。     

金矿渣和激发剂在少水泥熟料体系中的作用效果

为了促进金矿尾矿渣(简称金矿渣)在建材和少水泥熟料体系中的应用,在少水泥熟料体系中用金矿渣替代粉煤灰,并加入激发剂钾水玻璃、氢氧化钾和氢氧化钠,研究了硬化浆体组成和强度变化.结果表明:金矿渣取代粉煤灰量会影响激发剂的效果,取代量低时钾水玻璃的激发效果较显著,而取代量高时效果相反,这种差异性与激发剂对体系初始碱度和硅酸根基团贡献有关.     

Influence of elevated curing temperature on the properties of cement paste and concrete at the same hydration degree

Three different curing temperatures(20 ℃, 40 ℃, and 60 ℃) were set, so that the nonevaporable water(w_n) contents of plain cement pastes cured at these three temperatures were measured to determine the hydration degree of cement. Tests were carried out to compare the pore structure and strength of cement paste, as well as the strength and permeability of concrete under different temperature curing conditions when their cements were cured to the same hydration degree. The experimental results show that either at a relatively low hydration degree(w_n=15%) or high hydration degree(w_n=16.5%), elevated curing temperature has little influence on the hydration products of cement paste, while it has a negative influence on the pore structure and compressive strength of cement paste. However, this negative effect is weaker at high hydration degree. The large capillary pore(100 nm) volumes of cement pastes remain almost the same at high hydration degree, regardless of curing temperatures. As for the concrete, elevated curing temperature also has negative influence on its compressive strength development, at both low hydration degree and high hydration degree. And this negative effect is stronger than that on cement paste's compressive strength at the same hydration degree. On the whole, elevated curing temperature has little influence on the resistance of concrete to chloride ion penetration.     

添加剂对水泥性能与水化过程的影响

研究了单组分添加剂及其复合添加剂对水泥物理性能和水化特性的影响,结果表明：单组分添加剂对水泥的细度、净浆流动性、胶砂强度均有一定提高,复合添加剂的助磨、减水、增强效果均有大幅度提高,水泥80μm筛余降低45.8%,勃氏比表面积增加了14.0%,粒径为3-30μm的颗粒明显增多.水泥粉体的SEM分析表明：添加复合添加剂能显著降低粗颗粒的比例;水泥净浆流动度由135 mm提高到了190 mm;3 d、28 d强度提高了3.2MPa和7.4MPa.水泥水化样XRD分析表明：掺入复合添加剂能提高水泥的水化速率,促进水化产物的生成.     

Creep properties and resistivity-ultrasonic-AE responses of cemented gangue backfill column under high-stress area

To investigate the creep and instability properties of a cemented gangue backfill column under a highstress area, the uniaxial compression creep tests were conducted by single-step and multi-step loading of prismatic samples made of cemented gangue backfill material(CGBM) under the high stressstrength ratio. The creep damage was monitored using an electrical resistivity device, ultrasonic testing device, and acoustic emission(AE) instrument. The results showed that the CGBM sample has a creep hardening property. The creep failure strength(CFS) is slightly larger than the uniaxial compressive strength(UCS), ranging in ratio from 108.9% to 116.5%. The instantaneous strain, creep strain, and creep rate increase with increasing stress-strength ratio in the single-step loading creep tests. The instantaneous strain and creep strain decrease first and then increase during the multi-step loading creep process. The axial creep strain of the CGBM column can be expressed by the viscoelastic-plastic creep model. Creep instability is caused by the accumulation of strain energy under multi-step loading and the continuous lateral expansion at the unconstrained middle position during the creep process. The creep stability of a CGBM column in a high-stress area can be monitored based on the variation of electrical resistivity, ultrasonic pulse velocity(UPV), and AE signals.     

Spatiotemporal evolution of thermo-hydro-mechanical-chemical processes in cemented paste backfill under interfacial loadingOA

Cemented paste backfill(CPB) and rock interface interaction causes the formation of an interfacial loading and affects the thermal, hydraulic, mechanical, and chemical processes in bulk CPB and thus its in-situ behavior. In this study, a new meter-sized column model is developed to systematically investigate the multiphysics processes in CPB under interfacial loading. The obtained results discover that for the mechanical process, the interfacial loading leads to a reduced settlement and a weaken...     

Experimental study on the effect of granular backfill with various gradations on the mechanical behavior of rock

Backfilling is a common practice in the mining industry and the backfilling performance plays a significant role in supporting the surrounding rock mass. To evaluate the backfilling performance, an experimental apparatus has been developed to understand how backfill affects the compressive strength of sandstone specimens in the laboratory. Pebbles were selected to model the backfill and divided into six groups with different particle sizes using a set of standard sieves. The backfilling pebbles with three types of particle size compositions were then produced, i.e. single gradation, two adjacent gradations, and increasingly widening gradations. A series of compressive tests were carried out to study the mechanical behavior of the sandstone specimens confined by these pebbles. The effects of the gradations of the filled pebbles on the peak and residual compressive strengths were analyzed. It is found that the increasing amount of the compressive strength is over 10% in most cases, even up to 20%. Based on the experiment data, the increasing amount was also estimated theoretically under some assumptions and it further confirmed the experimental results. The effects are closely related to the gradations of the filled pebbles except for their dense degree.     

Influence of cellulose ethers on hydration products of portland cement

Cellulose ethers are widely used to mortar formulations,and it is significant to understand the interaction between cellulose ethers and cement pastes.FT-IR spectra,thermal analysis and SEM are used to investigate hydration products in the cement pastes modified by HEMC and HPMC in this article.The results show that the hydration products in modified cement pastes were finally identical with those in the unmodified cement paste,but the major hydration products,such as CH(calcium hydroxide),ettringite and C-...     

Effect of calcium aluminate cement variety on the hydration of portland cement in blended system

Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.     

Effect of superplasticizers on the early age hydration of sulfoaluminate cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fl uidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no infl uence on the further hydration of CSA cement, confi rmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio（0.45）. The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little infl uence on the early age hydration of the CSA cement.     

聚羧酸系减水剂对水泥水化过程的影响

研究了以聚乙二醇800、丙烯酸、顺酐、烯丙基磺酸钠、丙烯酸羟乙酯为原料合成的聚羧酸系XYZ18减水剂对水泥水化过程及微观结构的影响.结果表明,XYZ系减水剂具有缓凝特性,能减少并延缓水泥水化放热;使水泥早期微小晶体大量生长并填充孔隙,气孔细化且分布更加合理,晶体向外伸长使水泥粒子相互搭接而形成网络结构,提高了水泥石的密实性.