scholarly journals Using Coupled Rheometer-FBRM to Study Rheological Properties and Microstructure of Cemented Paste Backfill

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Hongjiang Wang ◽  
Liuhua Yang ◽  
Hong Li ◽  
Xu Zhou ◽  
Xiaotian Wang
Keyword(s):  
Shear Rate ◽  
Rheological Properties ◽  
Yield Stress ◽  
Rheological Behavior ◽  
Shear Thickening ◽  
Threshold Value ◽  
Rheological Parameters ◽  
Cemented Paste Backfill ◽  
Reflectance Measurement ◽  
Paste Backfill

Rheological properties, such as the yield stress, viscosity, and thixotropy, are related to the microstructure of cemented paste backfill (CPB). To highlight the relationship, two instruments were combined to measure the changes in the microstructure and the rheological properties of CPB simultaneously. In this way, the particle/agglomerate size distribution characterized by the focused beam reflectance measurement (FBRM) and the rheological factors measured by the rheometers could be directly linked. The results show that when under shearing, the intrinsic network structure of CPB responds to the shear-induced stresses with the interference of interparticle forces, leading to changes in the rheological behavior. Shear thinning can be found in CPB suspensions with a microstructure that is either loose interconnection or random. With an increase in the shear rate, random collisions among particles become organized in the flow, lowering the yield stress and viscosity. However, when the shear rate exceeds a certain threshold value, the rheological parameters change as a result of shear thickening. The results of this study contribute to better understanding of the complex rheological behavior of CPB.

scholarly journals Shear thinning and thickening of cemented paste backfill

2019 ◽  
Vol 29 (1) ◽  
pp. 80-93 ◽  
Author(s):  
Liuhua Yang ◽  
Hongjiang Wang ◽  
Aixiang Wu ◽  
Hong Li ◽  
Arlin Bruno Tchamba ◽  
...  
Keyword(s):  
Shear Rate ◽  
Rheological Properties ◽  
Yield Stress ◽  
Shear Thinning ◽  
High Shear ◽  
Cemented Paste Backfill ◽  
Concentrated Suspension ◽  
History Effects ◽  
Paste Backfill ◽  
Shear History

Abstract Cemented paste backfill (CPB) is considered to be a concentrated suspension in which tailings are bonded together by the hydraulic binder and water, and it has a high solid volume concentration (≥50 vol.%). Although the shear thinning and thickening of CPB has been extensively reported in literature, the shear history effects have been ignored in previous studies. In this paper, by using rheometer and Focused Beam Reflectance Measurement, the relationship between the rheological properties and microstructure of the paste under different shear histories was studied. The results have shown that at a low shear rate, CPB revealed shear thinning, low yield stress and low index parameters; while exhibited shear thickening, high yield stress and high consistency index when at high shear rates of shear history. This agreed with the general trends shown in the FBRM analysis. It was proposed that the action of shear is beneficial to particle dispersion, whereas a high shear rate history tends to promote the aggregation of particles. It was revealed that both shear thinning and thickening of paste are related to the situation of particles (flocculation, dispersion and aggregation), and shear history effects play an important role in rheological properties of CPB.

scholarly journals Rheological Properties of Cemented Paste Backfill with Alkali-Activated Slag

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 288 ◽  
Author(s):  
Yunpeng Kou ◽  
Haiqiang Jiang ◽  
Lei Ren ◽  
Erol Yilmaz ◽  
Yuanhui Li
Keyword(s):  
Yield Stress ◽  
Rheological Behavior ◽  
Plastic Viscosity ◽  
Molar Ratio ◽  
Cemented Paste Backfill ◽  
Lower Yield Stress ◽  
Alkali Activated Slag ◽  
Paste Backfill ◽  
Activated Slag ◽  
Alkali Activated

This study investigates the time-dependent rheological behavior of cemented paste backfill (CPB) that contains alkali-activated slag (AAS) as a binder. Rheological measurements with the controlled shear strain method have been conducted on various AAS-CPB samples with different binder contents, silicate modulus (Ms: SiO2/Na2O molar ratio), fineness of slag and curing temperatures. The Bingham model afforded a good fit to all of the CPB mixtures. The results show that AAS-CPB samples with high binder content demonstrate a more rapid rate of gain in yield stress and plastic viscosity. AAS-CPB also shows better rheological behavior than CPB samples made up of ordinary Portland cement (OPC) at identical binder contents. It is found that increasing Ms yields lower yield stress and plastic viscosity and the rate of gain in these parameters. Increases in the fineness of slag has an adverse effect on rheological behavior of AAS-CPB. The rheological behavior of both OPC- and AAS-CPB samples is also strongly enhanced at higher temperatures. AAS-CPB samples are found to be more sensitive to the variation in curing temperatures than OPC-CPB samples with respect to the rate of gain in yield stress and plastic viscosity. As a result, the findings of this study will contribute to well understand the flow and transport features of fresh CPB mixtures under various conditions and their changes with time.

scholarly journals Specific Mixing Energy of Cemented Paste Backfill, Part II: Influence on the Rheological and Mechanical Properties and Practical Applications

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1159
Author(s):  
Reagan Kabanga Dikonda ◽  
Mamert Mbonimpa ◽  
Tikou Belem
Keyword(s):  
Mechanical Properties ◽  
Rheological Properties ◽  
Yield Stress ◽  
Specific Energy ◽  
Distribution System ◽  
Flow Index ◽  
Cemented Paste Backfill ◽  
Practical Applications ◽  
Mixing Energy ◽  
Paste Backfill

The rheological properties (yield stress, flow index and infinite dynamic viscosity) and mechanical properties (unconfined compressive strength, UCS) of different cemented paste backfill (CPB) recipes must be determined during the laboratory optimization phase. However, the influence of the mixing procedure on these properties has scarcely been studied so far. The objective of this paper is to assess to what extent these properties depend on the specific mixing energy (SME) for a given type of mixer. CPB recipes were prepared based on two types of tailing (CPB-T1 and CPB-T2, also referred to as T1 and T2) at a fixed solid percentage for each type of tailing using the Omcan laboratory mixer. A mixture of 80% slag and 20% GU was used as a binder. The mixing time and the rotation speed of the mixer were successively varied. For each recipe prepared, we determined the SME, the rheological properties of fresh CPB (at the end of mixing) and the UCS at 7, 28 and 90 days of curing. The results show that yield stress and infinite viscosity decreased when SME increased in an interval going from 0.3 to 3.8 Wh/kg and 0.6 to 6 Wh/kg for CPB-T1 and CPB-T2, respectively. An increasing trend in UCS with increasing SME was also observed. Empirical equations describing the change of the rheological properties with the SME are used to estimate the change in rheological properties of CPB along the distribution system, considering the specific energy dissipation during CPB transportation. A mixing procedure for obtaining CPB mixtures that are representative of CPB deposited in underground mine stopes is suggested for laboratories who currently use a same mixing procedure, irrespective of the variable field specific energy.

scholarly journals Rheological Properties of Ultra-Fine Tailings Cemented Paste Backfill under Ultrasonic Wave Action

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 718
Author(s):  
Weicheng Ren ◽  
Rugao Gao ◽  
Youzhi Zhang ◽  
Maoxin Hou
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Ultrasonic Wave ◽  
Mass Concentration ◽  
Wave Action ◽  
Cemented Paste Backfill ◽  
Fine Tailings ◽  
Paste Backfill ◽  
Rheological Test ◽  
Positive Effect

Ultra-fine tailings cemented paste backfill (UCPB) exhibits special rheological characteristics with the effect of an ultrasonic sound field. In this study, in order to explore the thickening effect of slurry under ultrasonic wave action, we examined the rheological properties with ultrasonic wave tests of UCPB and the rheological properties after ultrasonic wave tests of UCPB. We found that the rheological curve of the slurry changed; the Herschel–Bulkley (HB) model in the initial state transformed into the Bingham model under the action of ultrasound. Ultrasonic waves have a positive effect on reducing slurry viscosity and yield stress. The rheological test of the slurry with ultrasonic wave action had a positive effect on significantly reducing the apparent viscosity and initial yield stress of slurry with a 62% mass concentration. The rheological test of slurry with ultrasonic wave action and the rheological test after ultrasonic wave action both have positive effects on reducing the viscosity and yield stress of the slurry with a 64% to 68% mass concentration; the overall effect of reducing the viscosity and yield stress of UCPB is greater after ultrasonic wave action of UCPB.

scholarly journals Effect of High Mixing Intensity on Rheological Properties of Cemented Paste Backfill

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 240 ◽  
Author(s):  
Liuhua Yang ◽  
Hongjiang Wang ◽  
Hong Li ◽  
Xu Zhou
Keyword(s):  
Rheological Properties ◽  
Fine Particles ◽  
Rheological Parameters ◽  
Cemented Paste Backfill ◽  
Mixing Intensity ◽  
Thixotropic Behavior ◽  
Paste Backfill ◽  
Structural Breakdown ◽  
Physical And Chemical ◽  
Insight Into

Cemented paste backfill (CPB) consists of a mixture of fine particles, mainly consisting of tailings and cement dispersed in water. Therefore, it is necessary to introduce an intensive shearing force into the paste during mixing in order to maintain an equilibrium between agglomeration and dispersion. It is influential for the macroscopical fluidity and rheological properties when changes occur in the microstructure of CPB under shear. However, the research on how mixing affects the properties of CPB is still in its infancy. This paper puts an insight into the relation between the mixing intensity and the rheological behavior of the CPB. It can be demonstrated that two threshold mixing intensities exist in this process. After passing the first or lower threshold, the rheological parameters (yield stress and viscosity) of the paste decrease. After passing the second threshold, a continued increase is observed. The changes in rheological properties are connected with physical and chemical changes in the microstructure of the CPB. The results are discussed in light of the three concepts “structural breakdown”, “thixotropic breakdown”, and “thixotropic behavior” of rheological properties of CPB.

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

2021 ◽  
Vol 28 (6) ◽  
pp. 1707-1723
Author(s):  
Qin-li Zhang ◽  
Yi-teng Li ◽  
Qiu-song Chen ◽  
Yi-kai Liu ◽  
Yan Feng ◽  
...  
Keyword(s):  
Rheological Properties ◽  
Cemented Paste Backfill ◽  
Ph Values ◽  
Paste Backfill

scholarly journals Investigating the Effect of Solid Components on Yield Stress for Cemented Paste Backfill via Uniform Design

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Yong Wang ◽  
Aixiang Wu ◽  
Lianfu Zhang ◽  
Fei Jin ◽  
Xiaohui Liu
Keyword(s):  
Yield Stress ◽  
Mass Fraction ◽  
Cement Content ◽  
Uniform Design ◽  
Free Water ◽  
Experimental Program ◽  
Cemented Paste Backfill ◽  
Free Water Content ◽  
Key Factor ◽  
Paste Backfill

Cemented paste backfill (CPB) technology has been applied quite popular around the world. Yield stress is a key factor determining whether CPB could be transported. In order to reveal the effect of solid components on yield stress of CPB, a uniform design experimental program (four factors and six levels) was conducted to test the rheological property of a mine’s CPB. The tested four factors including mass fraction, cement versus other solids ratio, coarse tailings, and gravel contents were considered during the experiment design. Likewise, six experimental levels were given to each factor. Results of the test show that yield stress increased with the mass fraction and cement content. However, the trend reversed for the content of coarse tailings and gravel. Contribution of the four factors to yield stress in descending order is mass fraction > content of gravel > content of coarse tailings > cement versus other tailings ration. Effect of solid components on the yield stress of CPB is mainly due to the different flocculation structure inside the CPB. These various flow structures result in the different free-water content of CPB, leading to a different yield stress value.

scholarly journals Effect of Pre-Shear on Agglomeration and Rheological Parameters of Cement Paste

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2173
Author(s):  
Mareike Thiedeitz ◽  
Inka Dressler ◽  
Thomas Kränkel ◽  
Christoph Gehlen ◽  
Dirk Lowke
Keyword(s):  
Yield Stress ◽  
Mixing Time ◽  
Length Distribution ◽  
Chord Length ◽  
Rheological Parameters ◽  
Reflectance Measurement ◽  
Time Dynamic ◽  
Chord Length Distribution ◽  
In Situ Investigation

Cementitious pastes are multiphase suspensions that are rheologically characterized by viscosity and yield stress. They tend to flocculate during rest due to attractive interparticle forces, and desagglomerate when shear is induced. The shear history, e.g., mixing energy and time, determines the apparent state of flocculation and accordingly the particle size distribution of the cement in the suspension, which itself affects suspension’s plastic viscosity and yield stress. Thus, it is crucial to understand the effect of the mixing procedure of cementitious suspensions before starting rheological measurements. However, the measurement of the in-situ particle agglomeration status is difficult, due to rapidly changing particle network structuration. The focused beam reflectance measurement (FBRM) technique offers an opportunity for the in-situ investigation of the chord length distribution. This enables to detect the state of flocculation of the particles during shear. Cementitious pastes differing in their solid fraction and superplasticizer content were analyzed after various pre-shear histories, i.e., mixing times. Yield stress and viscosity were measured in a parallel-plate-rheometer and related to in-situ measurements of the chord length distribution with the FBRM-probe to characterize the agglomeration status. With increasing mixing time agglomerates were increasingly broken up in dependence of pre-shear: After 300 s of pre-shear the agglomerate sizes decreased by 10 µm to 15 µm compared to a 30 s pre-shear. At the same time dynamic yield stress and viscosity decreased up to 30% until a state of equilibrium was almost reached. The investigations show a correlation between mean chord length and the corresponding rheological parameters affected by the duration of pre-shear.

scholarly journals Rheological behavior of cereal straw suspensions

2021 ◽  
Author(s):  
Sandra Ukaigwe
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Rheological Behavior ◽  
Xanthan Gum ◽  
Mesh Size ◽  
General Purpose ◽  
Measuring Instrument ◽  
Fiber Concentration ◽  
Cereal Straw ◽  
Malt Barley

The rheological properties (yield stress and viscosity) of cereal straw suspensions are especially important in bioethanol production as they determine the mixing behaviour of the suspension during enzymatic hydrolysis. Yield stress measurements are generally difficult to perform in straw suspensions due to sedimentation, which commonly occur in the suspensions because of the difficulty encountered in loading the suspension into the measuring equipment. The process of placing the suspension in the measuring instrument causes a disturbance likely to induce the yielding of the suspension before the actual measurements are taken. Moreover cereal suspensions at high straw concentration (10-40 wt%) are soft solids and pourability is particularly difficult with solids. Rheological behavior of staw suspensions made from wheat, Oats and malt barley of fiber sizes 0.15 mm-4.20 mm (mesh sizes 20 to 100) and concentrations 5.0-15.0 wt% were studied. The suspensions were initially prepared by dispersing milled and sieved straws in distilled water at room temperature, followed by vortexing to aid the dispersion process; this was later modified to include a 30-minute de-aeration of the suspensions using vacuum and 2-minute mixing using a general purpose mixer at about 162 rpm. However, none these procedures produced a homogenous suspension. The viscosity of the dispersion medium was modified by the addition of Xanthan gum. This produced homogenous suspensions which remained suspended for about 20 minutes. The rheological properties of these suspensions were measured on a Bohlin rheometer in the controlled stress mode using a vane and cup measuring instrument, and the suspension yield stress determined by extrapolation and by regression of Herschel-Bulkley, Casson and Bingham models. Yield stress obtained from extrapolation ranged from 2-19 Pa, while model results ranged from 0.96- 8.15 Pa, for 5.0 wt% Oats straw suspensions with Xanthan gum strengths of 0.1-0.5 wt%. Extrapolation results for 7.5 wt% Oats staw suspensions with Xanthan gum strengths of 0.1-0.5 wt% ranged from 20-36 Pa while model results were in the range of 4.38-18.76 Pa. Wheat and malt barely straw suspensions evaluated using Herschel-Bulkley model at similiar Oats straw suspension conditions of 5.0 wt% fiber concentration with 0.3 wt% Xanthan gum strength produced statistically equivalent yields stress to Oats straw suspensions in the range of 2.31-4.04 Pa for fibers of mesh size 40-100. Cereal straw suspenions are non-Newtonian fluids with yield stresses that are highly straw concentration dependent.

scholarly journals The influence of base oil type on the rheological properties of ecological lubricating greases

Nafta-Gaz ◽  
2021 ◽  
Vol 77 (2) ◽  
pp. 127-135
Author(s):  
Rafał Kozdrach ◽  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Rheological Properties ◽  
Measurement Data ◽  
Measuring System ◽  
Rheological Parameters ◽  
Flow Curves ◽  
Lubricating Grease ◽  
Dispersion Phase ◽  
Base Oil

The article presents the results of research on the influence the type of base oil in lubricating compositions has on the rheological parameters of selected lubricants. Vegetable, mineral, and synthetic dispersion phases were used to produce lubricating greases. The modified amorphous silica was used as the dispersed phase. However, as a modifying additive was used a substance containing the antioxidants, corrosion inhibitors, and EP/AW additives. The experiments on rheological properties were carried out using a Physica MCR 101 rotational rheometer (manufactured by Anton Paar), equipped with a diffusion air bearing and connected to a pneumatic supply – an oil-free Jun-Air compressor and air drying block. The device is equipped with a Peltier system for temperature control in the range of –20°C to 200°C and an external thermostatic VISCOTHERM V2 system, working in the temperature range of –20°C to 200°C. The rheometer control and measurement data analysis were performed using Rheoplus software. The tests were carried out using a cone-plate measuring system with a shear rate range of 0.01–100 s-1 at 20°C for lubricating compositions prepared on various oil bases. To evaluate the value of rheological parameters, the results of tests of the dependence between shear stress and shear rate (flow curves) were used. For the theoretical determined on the flow curves, the following rheological models were used: Bingham, Herschel–Bulkley, Casson, and Tscheuschner. The values of the shear stress (yield point) in depending on the type of dispersion phase has changed. This proves that the use of a base oil with the appropriate functional properties does not weaken, but reinforces the spatial structure of a lubricating grease. It has an important meaning when selecting construction parameters when designing a central lubrication system with grease made from a vegetable oil base (Abyssinian oil). The rheological properties of the lubricating grease are influenced by the type of base oil and thickener, any additives in the grease, the production technology of the grease, and the conditions in which it is used. The tests revealed an important influence of the base oil on the rheological parameters that describe the behaviour of lubricating compositions subjected to stresses and strains in a lubricating system.

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