Variability in rheology of cemented paste backfill with hydration age,binder and superplasticizer dosages

The use of (CPB) material to ameliorate geotechnical stability of underground mine is in nascent stage in India. Rheological properties of CPB change with travelling time as it is transported to underground mine stope through pipeline reticulation. In this paper, rheological properties of CPB based on mill tailings of a carbonate rich mineral processing waste are evaluated for different dosages of polycarboxylate (PC) based (SP). Each CPB sample having 78?wt% solids is mixed separately with 4%, 6% or 8% of binder dosages (ratio of the weight of dry binder to the weight of dry tailings) and, 0%, 0.5%, or 1.0% of SP dosages as weight of dry binder. The paper presents a methodology for determining yield stress, plastic viscosity and thixotropic behaviour of CPB mixture as a function of hydration age, binder and SP dosages. Results from the experimental campaigns indicate that SP content has significant influence on rheological behaviour of CPB and can be suitably exploited to enhance the flow characteristics of the carbonate rich process tailings. The study also develops multivariate linear regression models of yield stress, plastic viscosity and thixotropy of CPB depending on the hydration age, binder and SP dosages.     

Effects of activator type/concentration and curing temperature on alkali-activated binder based on copper mine tailings

This article investigates the effects of activator type/concentration and curing temperature on alkali-activated binder based on copper mine tailings (MT). Different alkaline activators including sodium hydroxide (NaOH), sodium silicate (SS), and sodium aluminate (SA) at different compositions and concentrations were used and four different curing temperatures, 60, 75, 90, and 120?°C, were considered. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), and X-ray diffraction (XRD) were conducted to investigate the effect of these factors on the unconfined compressive strength (UCS), microstructure, and phase composition of the binder. The results indicate that NaOH concentration and curing temperature are two important factors that affect the UCS and micro-structural properties of the alkali-activated MT binder. The optimum curing temperature, i.e., the curing temperature at the maximum UCS, depends on the NaOH concentration, lower optimum curing temperature at smaller NaOH concentration. Addition of aqueous SS to the NaOH solution can lead to strength improvement, with the highest UCS obtained at a SiO₂/Na₂O ratio of 1.0–1.26. Addition of powder SA to the NaOH solution profoundly delays the setting at 60?°C but improves the UCS at 90?°C. The SEM/EDX results show highly heterogeneous microstructure for the alkali-activated MT binder as evidenced by the variable Si/Al ratios in different phases. The XRD patterns indicate a newly formed crystalline phase, zeolite, in the 90?°C-cured specimens. The results of this study provide useful information for recycling and utilization of copper MT as construction material through the geopolymerization technology.     

Coupled thermo-hydro-chemical effect on rheological behavior of fresh cemented tailings backfill

Cemented tailings backfill (CTB) is a mixture of tailings, binder and water. The freshly prepared CTB slurry is commonly transported into underground mined-out areas via pipeline. The flowability of fresh CTB slurry is significantly affected by the coupled thermal (T), hydraulic (H), rheological (R) and chemical (C) processes. Therefore, this paper develops a THRC coupling model, which considers the evolutions of thermal conduction, fluid flow, rheology, and binder hydration to predict the fluidity of fresh CTB slurry. Rheological testing experiments are conducted to verify the availability of the developed model. The validated model is used to further investigate the effect of time and temperature factors on the hydraulic behavior of the hydrating CTB slurry. The obtained outcomes can make contributions to a better regulation of the time and temperature factors in the preparation and transportation of fresh CTB slurry.     

Strength and self-desiccation of slag-cemented paste backfill at early ages: Link to initial sulphate concentration

This paper presents the results of an experimental study on the early age strength and changes in the self-desiccation process of cemented paste backfill (CPB) that contains blast furnace Slag (Slag-CPB) and sulphate. Slag-CPB samples with different initial sulphate concentrations (0, 5000, 15,000 and 25,000 ppm) are prepared and cured in well-sealed molds at early ages (1, 3, 7 and 28 days) in room temperature (∼23 °C). Mechanical and hydraulic conductivity tests are performed on the samples, in which the suction and electrical conductivity of the Slag-CPB specimens are monitored. Furthermore, microstructural analyses are conducted on the Slag-CPB and slag-cement paste samples. The results show that sulphate can have a positive or negative effect on the early age strength and self-desiccation of Slag-CPB, i.e., cause an increase or decrease in strength and acceleration or reduction in the amount and rate of self-desiccation, depending on the initial sulphate content and curing time. This study also shows that an understanding of the positive or negative effect of sulphate on the early strength and self-desiccation of Slag-CPB is critical for designing cost-effective CPB structures with high early strength, speeding up mining cycles or assessing the deterioration of CPB caused by high sulphate attack to ensure safety in mining.     

Coupled effects of sulphate and temperature on the strength development of cemented tailings backfills: Portland cement-paste backfill

Cemented paste backfill (CPB), which is a mix of tailings, water and cement, is subjected to the combined actions of temperature and sulphate during its service life. There is a need to acquire solid knowledge on the coupled effects of temperature and sulphate on the strength of CPBs for a safe, durable and cost-effective design of CPB structures. Hence, the main objective of this paper is to use an experimental approach to study the combined effect of temperature and sulphate on the strength development and microstructure (mineralogical composition of the hardened cement paste) of CPBs. About 200 CPB specimens with various initial sulphate contents (0, 5000, 15,000, and 25,000 ppm) and cured at different temperatures (0 °C, 25 °C, 20 °C, 35 °C, and 50 °C) are tested at different curing times (28, 90, and 150 days). The results show that the coupled effect of temperature and sulphate has a significant impact on the strength and mineralogical composition of the CPB. Depending on the curing time, temperature and initial sulphate content, the sulphate can have a positive or negative impact, i.e., leads to an increase or decrease of CPB strength. The obtained results show a strong indication that the absorption of sulphate by calcium–silicate–hydrate (C–S–H) could lead to the formation of lower quality C–S–H, thereby decreasing the strength of the CPB. This study has demonstrated that the coupled effect of sulphate and temperature on CPBs is an important factor for consideration in the designing of cost-effective, safe and durable CPB structures.     

Experimental investigation into the compressive strength development of cemented paste backfill containing Nano-silica

This paper investigates the influence of Nano-silica (NS) addition on the consistency and compressive strength development of cemented paste backfill (CPB). Tetraethyl-Orthosilicate (TEOS) was used as the precursor of Nano-silica along with ether-based Polycarboxylate superplasticizer (PCS). Two binder types (Portland cement and Slag-cement) and different amounts of TEOS (0.7–14% by mass of binder) with and without PCS are examined for 3, 7, 14, and 28 days curing time. Uniaxial compression tests for unconfined compressive strength (UCS) determination, slump height measurement, changes in gravimetric water content, and differential thermogravimetric analysis (DTG) were used to assess the influence of NS and admixtures (TEOS-PCS) on CPB performance. The results of this experimental study indicate that the addition of approximately 5% TEOS along with 0.5% PCS (by mass of binder) provide the best compressive strengths that can also be anticipated through the higher amount of calcium silicate hydrate (CSH) on DTG curves. It is also noticeable that the positive influence of NS is more evident when the amount of binder was decreased. The addition of PCS to CPB containing NS improved both the consistency of the mixture and the compressive strength development of CPB.     

Initial temperature-dependence of strength development and self-desiccation in cemented paste backfill that contains sodium silicate

Advanced knowledge of the effect of the initial temperatures of cemented paste backfill (CPB) on its strength development and self-desiccation ability is needed to provide a rational basis for mixture proportioning as well as the cost-effective design of CPB structures and speeding up of the mining cycle. An experimental testing and monitoring program has been undertaken to determine the influence of various initial temperatures (2 °C, 20 °C, 35 °C and 50 °C) on the strength development and evolution of the self-desiccation (measured by the volumetric water content and suction) of the CPB that contains sodium silicate as the admixture (S-CPB) at early ages (up 28 days). The evolution of the temperature, electrical conductivity (gives information about the cement hydration progress), volumetric water content and suction of S-CPB samples with the specified initial temperatures have been monitored for 28 days. Moreover, mechanical tests and microstructural analyses are performed on these S-CPB specimens after specific curing times (6 h, 1 day, 3 days, 7 days and 28 days). The results obtained show that the initial backfill temperature has a significant influence on the curing temperature of S-CPB, its strength development and self-desiccation. Furthermore, the results reveal that the temperature-time history, cement hydration, self-desiccation and strength development of S-CPB are strongly coupled. The initial S-CPB and these couplings should be taken into account for a safe and economical design of S-CPB structures and the speeding up of mining cycles.     

Influence of visco-elastic binder properties on ram extrusion of a hardmetal paste

The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide–cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30–42 °C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow–Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, σ₀, increased linearly with the binder elastic modulus, G′, while both the velocity dependence parameters α and β were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2–5 particle diameters.     

Combined influence of sulphate and temperature on the saturated hydraulic conductivity of hardened cemented paste backfill

This paper presents an experimental study that focuses on the investigation of the coupled effects of temperature and sulphate on the permeability of hardened cemented paste backfill (CPB). Hydraulic conductivity tests and a microstructural analysis are conducted on mature CPBs prepared with various amounts of sulphate (0, 5000, 15,000, and 25,000 ppm) and cured at various temperatures (2 °C, 20 °C, 35 °C, and 50 °C). Important findings and valuable results are gained. It is found that the coupled effects of sulphate and temperature can lead to decrease (i.e. improvement of the environmental performance of CPBs) or increase of the hydraulic conductivity of CPBs. There is competition between the permeability decreasing and increasing factors. The dominant influencing factors depend on the curing temperature and initial sulphate content.     

Experimental characterization of the stress–strain behaviour of cemented paste backfill in compression

It is of great interest for economical and security reasons to understand the compressive properties of underground cemented paste backfill. In this paper, the stress–strain behaviours of cemented paste backfill (CPB) subjected to uniaxial compression and conventional triaxial tests are presented and discussed. The effect of CPB basic components, strength, ageing and confining pressure on the deformation behaviour of CPB are evaluated and discussed. The results show that the stress–strain behaviour of CPB is strongly influenced by the confinement, the age and strength of CPB, and its components. The increase in confining pressure leads to a change in the mode of failure, in the stiffness, and an increase in the strength.     

Dynamic tests of cemented paste backfill: effects of strain rate,curing time,and cement content on compressive strength

This article investigates the compressive strength of cemented paste backfill (CPB) under dynamic loading. To accommodate the low impedance CPB, a modified split Hopkinson pressure bar (SHPB) system is adopted. In contrast to traditional solid steel transmitted bar, a hollow aluminum transmitted bar is introduced to reduce the impedance. With this system, the dynamic stress equilibrium is achieved, which guarantees the valid dynamic material testing condition. The dynamic tests are conducted for CPB with different cement contents and curing time. It is observed that: (1) for CPB with the same curing time and cement content, the dynamic strength increases with the strain rate, (2) for CPB with the same cement content, the dynamic strength increases with the curing time, and (3) for CPB with the same curing time and tested under similar strain rate, the dynamic strength increases with the percentage of cement. This observation can be understood by considering the hydration process of cements.     

Effect of binder liquid type on spherical crystallization

Aim: Spherical crystallization is a process of formation of agglomerates of crystals held together by binder liquid. This research focused on understanding the effect of type of solvents used as binder liquid on the agglomeration of crystals.

Method: Carbamazepine and ethanol/water were used respectively as a model drug and crystallization system. Eight solvents as binder liquid including chloroform, dichloromethane, isopropyl acetate, ethyl acetate, n-hexane, dimethyl aniline, benzene and toluene were examined to better understand the relationship between the physical properties of the binder liquid and its ability to bring about the formation of the agglomerates. Moreover, the agglomerates obtained from effective solvents as binder liquid were evaluated in term of size, apparent particle density and compressive strength.

Results: In this study the clear trend was observed experimentally in the agglomerate formation as a function of physical properties of the binder liquid such as miscibility with crystallization system. Furthermore, the properties of obtained agglomerates such as size, apparent particle density and compressive strength were directly related to physical properties of effective binder liquids.

Conclusion: Results of this study offer a useful starting point for a conceptual framework to guide the selection of solvent systems for spherical crystallization.     

新拌水泥浆体中邻近胶凝材料粒子表面最近间距分布的解析解

依据Torquato的最邻近表面函数公式, 推导了新拌水泥浆体邻近水泥粒子表面最近间距分布的解析解, 并采用计算机模拟生成了1个水泥浆体结构模型, 选取邻近粒子表面最近间距概率密度分布曲线、 区间概率曲线和累计概率分布曲线这3个函数检验模拟结果与理论结果之间的差别。结果表明, 该解析解与计算机模拟实验结果吻合良好。利用该解析解, 以Rosin-Rammler分布为例, 研究了胶凝材料细度以及水胶比对邻近水泥粒子表面最近间距分布及其平均值的影响。结果显示, 水泥细度对邻近粒子表面最近间距平均值的影响高于水胶比的影响。邻近粒子表面最近间距解析解的获得, 不但为基于不同粒径分布以及尺度范围粉体之间搭配的高粉体初始堆积密度的实现提供了依据, 而且对多尺度模拟方法中选取各级模型的尺度、 量化粉煤灰浆体中粉煤灰颗粒的微集料效应、 了解邻近集料间的交互作用程度以及界面重叠程度等问题具有参考价值。     

Effect of binder type and content on physical and mechanical properties of geopolymers

In this study, the physical and mechanical behaviors of geopolymers prepared by using different amounts of silica fume and calcium hydroxide as binding materials, acidic pumice as fine aggregate and waste aluminium particles as air-entraining agent were investigated. Test results showed that binder types, amount of binders and alkali activator (sodium hydroxide) significantly affected the physical and mechanical behavior of geopolymer specimens. Bulk density, compressive and flexural strength decreased with the higher alkali activator content. Addition of waste aluminium particles led to decrease in bulk density and strength due to the some extent of entrained air. In the case of same alkali activator content, compressive and flexural strength increased with increase in silica fume and calcium hydroxide up to a certain level.     

Effect of particle-size distribution and specific surface area of different binder systems on packing density and flow characteristics of cement paste

The particle-size distribution (PSD) and specific surface area (SSA) of binders significantly affect the fresh and hardened characteristics of cement-based materials. An experimental investigation was undertaken to evaluate the influence of PSD and calculated SSA of various binary and ternary binder systems on flow characteristics, packing density, and compressive strength development of cement paste. The influence of dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum water demand (OWD) needed to achieve maximum wet density. The modified Andreasen and Andersen (A&A), Rosin–Rammler (RR), and power law grading models were employed to optimize the PSD of binder system to achieve maximum packing density, while maintaining relatively low water demand. The incorporation of high-range water reducing admixture (HRWRA) is shown to decrease the OWD and increase the packing density resulting from greater degree of dispersion of the binder. The combined effect of lower OWD, greater packing density, and higher SCM reactivity results in higher compressive strength. The increase in SSA from 425 to 1600 m²/kg results in an enhancement in packing density from 0.58 to 0.72, while further increase in SSA from 1600 to 2200 m²/kg reduces the packing density from 0.72 to 0.62. Binder systems using a distribution modulus between 0.21 and 0.235 determined from the A&A model exhibited 18%–40% lower minimum water demand (MWD) to initiate flow, 8%–35% higher OWD to reach maximum wet density, and 15%–25% higher packing density compared to the binder with 100% cement. Binder systems with lower A&A distribution modulus resulted in higher relative water demand (RWD) required to increase fluidity, thus reflecting greater level of robustness. Good correlations were established between the A&A distribution modulus, SSA, RR spread factor, and power law distribution exponent.     

Preparation and characterization and release properties of Eudragit RS based ibuprofen pellets prepared by extrusion spheronization: effect of binder type and concentration

Objective: The effects of type and concentration of binding agent on properties of Eudragit RS based pellets were studied.

Materials and methods: Pellets containing ibuprofen (60%), Eudragit RS (30%), Avicel (10%) were prepared by extrusion spheronization. PVP K30, PVP K90, HPMC 6cp, HPMC K100LV or HPMC K4M were used as binders in concentrations of 2, 4 or 6% based on the total weight of formulation. The process efficiency, pellet shape, size distribution, crushing strength, elastic modulus and drug release were examined. The effect of curing on pellet properties was also investigated.

Results: The process of extrusion spheronization became difficult with increase in binder viscosity and/or concentration. An increase in binder viscosity and/or concentration resulted in reduction in the yield of pellets, wider particle size distribution and departure from spherical shape especially in the case of HPMC binder. The crushing strength and elastic modulus of pellets decreased with increase in PVPs concentration. However this was not the case for pellets containing HPMCs. Drug release rate increased as the concentration of binder increased. Pellets containing 2%w/w of PVP K30 showed the slowest release rate. For those pellets with brittle nature, curing changed the behavior of pellet under mechanical test to plastic deformation. Yield point and elastic modulus of all formulations decreased after curing. Curing decreased the drug release rate.

Conclusion: Binder type and concentration significantly affected the properties of pellets. For production of sustained release ibuprofen Eudragit RS based pellets lower viscosity binders (PVP K30) with concentrations less than 4%w/w was optimum.     

温拌剂种类及掺量对不同沥青流变性能的影响

为了研究温拌剂种类及掺量对沥青流变性能的影响,通过动态剪切流变仪对分别掺加RH和Evotherm温拌剂的SBS改性沥青和基质沥青进行温度扫描试验,分析了它们的复数剪切模量、相位角和车辙因子。结果表明,Evotherm温拌剂在28~52℃能够提升两种沥青抗车辙性能,52℃后效果减弱;并且在28~40℃间可以提高两种沥青弹性恢复性能,40℃后会使SBS改性沥青弹性恢复性能减弱,对基质沥青无影响。增加Evotherm温拌剂掺量,在28~52℃会使温拌SBS改性沥青抗车辙性能提高,使温拌基质沥青抗车辙性能有所减弱,52℃后影响不明显。RH温拌剂在28~46℃对两种沥青抗车辙性能略有不利,但负面作用随温度升高逐渐减弱甚至消失;RH温拌剂能够显著增大两种沥青高温时弹性恢复性能。RH温拌剂掺量增大会使两种沥青抗车辙性能降低,但会使弹性恢复性能增强。     

Comparative life cycle assessment (LCA) of bio-modified binder and conventional asphalt binder

This study is a life cycle assessment (LCA) of conventional asphalt binder versus bio-modified binder that is produced by mixing asphalt binder with bio-binder obtained from swine manure. Both processes were evaluated and compared in terms of their contribution to global warming, using a global warming potential index and energy consumption. This LCA study uses a cradle-to-gate approach for the binder and includes a comparison between the environmental impacts of swine manure in lagoons and the production of bio-binder. The results show the energy consumption and global warming potential improvements after using bio-binder as a sustainable additive.     

Heat deformations of cement paste phases and the microstructure of cement paste

The paper presents the results of an experimental investigation of the influence of thermal deformations of phases present in hardened cement paste on its microstructure. For the observation of the thermal deformation course in the range of temperature20–800°C, a method of complex thermal analysis (DTA, DTD, TD) was employed. The microstructure of heated cement pastes was observed by both optic and electron microscopes. From an analysis of the results of the investigation it has been found that chemical processes stimulated by temperature in particular phases of cement paste have a significant influence on the thermal deformation course. It is shown that micracracks caused by different thermal deformations, appear first in the aregas of Ca (OH)₂ concentration (ca.300°C), and next (ca.400°C) as well as in the areas of occurrence of unhydrated large clinker grains.

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Résumé On rend compte d'une étude expérimentale sur les causes de la destruction de la microstructure de la pate de ciment portland exposée à la chaleur dans une gamme de températures allant de20 à800°C. On a prêté une attention particulière aux déformations thermiques de chacune des phases reconnues de la pate de ciment durci. On a utilisé une méthode d'analyse thermique complexe (DTA, TD, DTD) pour l'étude de l'évolution de déformations thermiques. On a observé les microstructures de la pate de ciment chauffée au microscope optique et électronique. On a étudié les phases suivantes de la pate de ciment: clinkers (C₃S, β-C₂S, C₃A, C₄AF), minéraux hydratés de ciment (hydrates C₃S, β-C₂S, C₃A, C₄AF), et produits d'hydratation [Ca(OH)₂, ettringite]. Les résultats de l'étude ont permis à l'auteur de déterminer l'allure de la déformation thermique des phases que présente la pate de ciment durcie sous températures croissantes. On a constaté que les processus chimiques que l'élévation de température induit dans chacune des phases de la pate de ciment exercent une influence notable sur l'évolution des déformations thermiques. Les microfissures causées par différentes déformations thermiques des phases apparaissent dans les zones de concentralisation de Ca(OH)₂ à environ300 et400°C aussi bien que dans les zones où se rencontrent des grains de clinker non hydraté.