scholarly journals Assessment of Hydration Process And Mechanical Properties of Cemented Paste Backfill By Rebound Method

2021 ◽  
Author(s):  
Sa Huang ◽  
Yongyan Wang ◽  
Zhuoqun Yu ◽  
Peng Du ◽  
Zhonghao Liang
Keyword(s):  
Functional Model ◽  
Quadratic Function ◽  
Hardness Test ◽  
Filling Material ◽  
Mining Method ◽  
Function Model ◽  
Unconfined Compression Test ◽  
Curing Conditions ◽  
Local Strength ◽  
Paste Backfill

Abstract Backfilling mining method is a green mining method which is being used widely, nevertheless, the uniaxial compressive strength (UCS) of the cement backfill paste (CPB) on site is difficult to measure, and it is impossible to know the internal cementation, for this reason, the rebound method is improved and introduced in this paper. Standard specimens of CPB were made and cured for different curing age under standard curing conditions. The hardness test of each part of the CPB is completed, the unconfined compression test is carried out, and the functional model of the hardness of each part of the CPB is established, which was a function of radius and age. Based on the nonuniformity of the filling material, the failure mode of CPB is analyzed and verified in the test. The results show that the exponential function model is more suitable for the relationship between the external hardness and the overall strength, and this conclusion is of great significance in construction site. In addition, the corresponding relationship between hardness and local strength was calculated and verified, the results show that the simple model can predict the variation of local strength with hardness better, and the quadratic function model is the best choice.

scholarly journals Mine Backfilling in the Permafrost, Part I: Numerical Prediction of Thermal Curing Conditions within the Cemented Paste Backfill Matrix

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 165 ◽  
Author(s):  
Fabrice Beya ◽  
Mamert Mbonimpa ◽  
Tikou Belem ◽  
Li Li ◽  
Ugo Marceau ◽  
...  
Keyword(s):  
Temperature Field ◽  
Numerical Models ◽  
Three Dimensional ◽  
Equilibrium Temperature ◽  
Cemented Paste Backfill ◽  
Thermal Curing ◽  
Curing Conditions ◽  
Permafrost Rock ◽  
Thermal Boundary Conditions ◽  
Paste Backfill

The mechanical behavior of cemented paste backfill (CPB) in permafrost regions may depend on the thermal curing conditions. However, few experimental data are available for calibrating and validating numerical models used to predict these conditions. To fill this gap, a three-dimensional (3D) laboratory heat transfer test was conducted on CPB placed in an instrumented barrel and cured under a constant temperature of −11 °C. Results were used to calibrate and validate a numerical model built with COMSOL Multiphysics®. The model was then used to predict the evolution of the temperature field for CPB cured under the thermal boundary conditions for a backfilled mine stope in the permafrost (at −6 °C). Numerical results indicated that the CPB temperature gradually decreased with time such that the entire CPB mass was frozen about five years after stope backfilling. However, the permafrost equilibrium temperature of −6 °C was not reached throughout the entire CPB mass even after 20 years of curing. In addition, the evolution of the temperature field in the permafrost rock showed that the thickness of the thawed portion reached about 1 m within 120 days. Afterwards, the temperature continues to drop over time and the thawed portion of the permafrost refreezes after 365 days.

scholarly journals Effect of the Initial Air Content in Fresh Slurry on the Compressive Strength of Hardened Cemented Paste Backfill

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Youzhi Zhang ◽  
Deqing Gan ◽  
Zhenlin Xue ◽  
Xun Chen ◽  
Sheng Hu
Keyword(s):  
Compressive Strength ◽  
Sodium Dodecyl ◽  
Contact Structures ◽  
Cemented Paste Backfill ◽  
Mining Method ◽  
Force Analysis ◽  
Air Content ◽  
Ground Pressure ◽  
Paste Backfill ◽  
The Mathematical Model

Filling mining method can dispose of the tailings into filling slurry, which can be transported to the stope through pipelines to manage the ground pressure and protect the environment. To improve the flowability of filling slurry, additives are used more and more widely. However, some additives can increase the air content in the slurry. The air in the slurry will become pores in the hardened cemented paste backfill (CPB). Therefore, it is necessary to explore the influence of initial air content in fresh slurry on the compressive strength of CPB. In this paper, sodium dodecyl sulfate (SDS) was used to regulate the air content in the fresh slurry. After measuring the initial air content, the slurry was made into test blocks. Then, the uniaxial compressive strength (UCS) of CPB at 28 d age was tested, and the distribution of CPB microscopic pores was observed by scanning electron microscope (SEM). The results show that as the initial air content in fresh slurry increases, the UCS of CPB first increases and then decreases. Before the initial air content in fresh slurry is 6.03%, the CPB pores distribution is relatively uniform. However, after exceeding this value, “discontinuous contact” structures, pore groups, and macropores occur in CPB. Through the CPB microscopic force analysis, the mathematical model describing the effect of initial air content on UCS of CPB should be a combination of logarithmic function and quadratic polynomial. This work can provide a supplement to the theory of CPB strength.

Research on Function Model of Binary Code

2012 ◽  
Vol 198-199 ◽  
pp. 374-379
Author(s):  
Wei Gao ◽  
Jing He ◽  
Ke An ◽  
Hong Xia Gao ◽  
Cheng Liu
Keyword(s):  
Binary Code ◽  
Functional Model ◽  
Control Flow ◽  
Control Flow Graph ◽  
Function Model ◽  
Flow Graph ◽  
Storage Structure ◽  
Reverse Analysis

The paper presents a reverse analysis and crack-found methodology with the functional model as the centre for OS trusted mechanism, pays attention to the functional model establishing of binary code and the description methodology. And it designs general XML-based storage structure to serve the storage and transformation of information cross levels in the level functional model of trusted mechanism, develops the plugin of IDA, which takes and stores routine Control Flow Graph and level functional model automatically from the binary code.

scholarly journals 3D Numerical Modelling of the Application of Cemented Paste Backfill on Displacements around Strip Excavations

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7750
Author(s):  
Krzysztof Skrzypkowski
Keyword(s):  
Numerical Modeling ◽  
Cement Content ◽  
Cemented Paste Backfill ◽  
Mining Method ◽  
3D Numerical Modeling ◽  
Compressibility Coefficient ◽  
3D Numerical Modelling ◽  
Paste Backfill ◽  
First Time ◽  
Cylindrical Samples

This article presents laboratory and spatial numerical modeling of cemented paste backfill. The first part of the research concerned laboratory tests of a mixture of sand, water, and variable cement content (5%, 10%, and 15%). The density and curing time of the mixture were determined. Moreover, cylindrical samples with a diameter of 46 mm and a height of 92 mm were constructed, for which compressive and tensile strength were calculated after one, two, three, and four weeks. The second part of the research concerned 3D numerical modeling with the use of RS3 software. For the exploitation field with dimensions of 65 m × 65 m, a strip-mining method was designed. The main objective of the research was to determine the changes in displacements around the haulage room and transportation roadway located in the immediate vicinity of the exploitation field. For the first time in numerical modeling, a two-sided strip method was used for the four stages of mining the ore deposit where the post-mining space was filled with a cemented paste backfill. Based on this research, the compressibility coefficient was determined.

scholarly journals Experimental investigation of concrete strength curve based on pull-out post-insert method

2020 ◽  
Vol 16 (7) ◽  
pp. 155014772094402
Author(s):  
Yuanxun Zheng ◽  
Weixing Kong ◽  
Mengen Ji ◽  
Chao Wan ◽  
Ehsan Moshtagh
Keyword(s):  
Concrete Strength ◽  
Standard Condition ◽  
Core Sample ◽  
Curing Conditions ◽  
Pull Out ◽  
Local Strength ◽  
Engineering Significance ◽  
Strength Curve ◽  
Reference Index ◽  
Drilling Core

As concrete is a building material that is widely used in the field of infrastructure construction, and its quality is related to the quality and service life in infrastructure engineering, concrete strength is an important reference index that reflects the concrete quality. Based on this, two commercial concretes A and B are selected in Henan Province, China, to perform the concrete strength test under same condition curing and standard condition curing in the pull-out post-insert method, cubic compression, rebound method, and drilling core method. The relationships between the different curing conditions, cubic compressive strength, core sample strength, rebound strength, and pull-out force of different commercial concretes are compared and analyzed. Through a comparative analysis and while considering the convenience and accuracy requirements, the strength curves of the two different concretes based on the pull-out post-insert method were fitted and analyzed, and the local strength curve test in Henan based on the pull-out post-insert method was established. The research results provide technical support for evaluating the strength of concrete structures using the pull-out post-insert method, which has important engineering significance for improving the popularize and application of the pull-out post-insert method.

Current Situation and Prospect of Coal Backfill Mining Technology

2012 ◽  
Vol 524-527 ◽  
pp. 421-425 ◽  
Author(s):  
Wen Yu Lv ◽  
Zhi Hui Zhang
Keyword(s):  
Mining Method ◽  
Abscission Layer ◽  
Mining Technology ◽  
Backfill Mining ◽  
Paste Backfill ◽  
Rock Movement ◽  
Mining Capacity ◽  
Mining Design

This paper introduces the classification of the coal backfill mining method and analyzes current technology statuses of several coal backfill mining technologies: waste backfill mining technology, paste backfill mining technology and abscission layer grouting backfill mining technology. Based on the analysis of current backfill mining technology statuses, this paper puts forth that the backfill mining technology should focus on the problem of the lack of coal backfill mining capacity, research on the role of backfill mining rock movement needing to be strengthened, filling efficiency and economy needed to improved through reasonable optimization of backfill mining parameter, so it can provide the theoretical basis for backfill mining design.

scholarly journals Insight into Saturated Hydraulic Conductivity of Cemented Paste Backfill Containing Polycarboxylate Ether-Based Superplasticizer

Minerals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 93
Author(s):  
Sada Haruna ◽  
Mamadou Fall
Keyword(s):  
Hydraulic Conductivity ◽  
Environmental Performance ◽  
Mining Industry ◽  
Design Criterion ◽  
Saturated Hydraulic Conductivity ◽  
Curing Temperature ◽  
Partial Replacement ◽  
Cemented Paste Backfill ◽  
Curing Conditions ◽  
Paste Backfill

Recycling of tailings in the form of cemented paste backfill (CPB) is a widely adopted practice in the mining industry. Environmental performance is an important design criterion of CPB structures. This environmental performance of CPB is strongly influenced by its saturated hydraulic conductivity (permeability). Superplasticizers are usually added to improve flowability, but there is a limited understanding of their influence on the hydraulic properties of the CPB. This paper presents new experimental results on the variations of the hydraulic conductivity of CPB containing polycarboxylate-based superplasticizer with different compositions and curing conditions. It is found that the hydraulic conductivity of the CPB decreases with the addition of superplasticizer, which is beneficial to its environmental performance. The reduction is largely attributable to the influence of the ether-based superplasticizer on particles mobility and cement hydration. Moreover, both curing temperature and time have correlations with the hydraulic conductivity of CPB containing superplasticizer. In addition, the presence of sulfate and partial replacement of PCI with blast furnace slag reduces the hydraulic conductivity. The variations are mainly due to the changes in the pore structure of the CPB. The new results discussed in this manuscript will contribute to the design of more environmental-friendly CPBs, which is essential for sustainable mining.

scholarly journals A Strengthening Mechanism and Influencing Factors of Coal Fly Ash using Microbial-Induced Carbonate Precipitation

2021 ◽  
Author(s):  
Shuaifeng Wu ◽  
Hong Cai ◽  
Ran Wei ◽  
Jianzhang Xiao ◽  
Jun Yan ◽  
...  
Keyword(s):  
Fly Ash ◽  
Calcium Carbonate ◽  
Influencing Factors ◽  
Fine Particles ◽  
Coal Fly Ash ◽  
Carbonate Precipitation ◽  
Filling Material ◽  
Dust Suppression ◽  
Curing Conditions ◽  
Nutrient Salt

Abstract Coal fly ash (CFA) that is discharged from coal-fired power plants has characteristics of fine particles, a small specific gravity and a large pore ratio. The dust suppression and strengthening of CFA is usually carried out by spraying water in the ash storage yard, but this practical approach is unsatisfactory. The strength of the CFA filling material affects the construction safety and operational safety of the ash dams. To carry out effective CFA material utilization and dust-pollution control, this paper applied the microbial-induced carbonate precipitation (MICP) method to enhance the strength of CFA under two curing conditions of natural evaporation (NE) and in a moisture cylinder (MC). The microbial-reaction mechanism, strengthening characteristics and influencing factors were studied. The results show that: 1) the calcium carbonate that is produced by microorganisms in the CFA is calcite, and the calcium-carbonate content increases from 7% to 18.9% and 15.3% under the MC and NE curing conditions, respectively; 2) MICP can improve the CFA strength, and the unconfined compressive strength can be increased by 6.55 times to 97.63 kPa under the MC curing conditions; 3) the solidification strength of CFA varies significantly with the concentration of CaCl2.2H2O and CH4N2O nutrients. The peak stress increases initially and then decreases with an increase in nutrient salt concentration. The optimum nutrient concentration was 0.5 mol/L and 1.0 mol/L for the MC and NE curing conditions, respectively; 4) calcium carbonate that was induced by microbial reaction can reduce the water loss in the ash specimen, and allow the ash surface to form a better water-retention effect, with good prospects for dust suppression.

scholarly journals Logarithmic Quadratic Regression Model for Early Periods of COVID-19 Epidemic Count Data

2020 ◽  
Author(s):  
Daisuke Tominaga
Keyword(s):  
Differential Equation ◽  
Regression Model ◽  
Linear Model ◽  
Generalized Linear Model ◽  
Early Period ◽  
Quadratic Function ◽  
Compartment Model ◽  
Function Model ◽  
Epidemic Curve ◽  
Transition Mechanism

Abstract Background While COVID-19 epidemic has been spreading worldwide, its characteristics are still unclear. The development of good mathematical models for predicting its prevalence and subsiding is strongly expected. The epidemic curve shows how the epidemic increases and subsides. This is the number of persons found infected daily. To express this with a mathematical model, the compartment model such as the SIR model is used generally. However, model parameter values of these ordinary differential equation based models are very sensitive for errors of observed data, and it is often difficult to find a reliable model especially when the amount of data is not sufficient. On the other hand, a regression model with a small number of parameters is more robust against data errors than a highly sensitive nonlinear differential equation model, though, it is not clear what a good regression model is for epidemic data. MethodsWe modeled the initial emerging period of the epidemic curve of COVID-19 in Tokyo with a model that introduces a quadratic polynomial function to the logarithms of the numbers of infected cases, and modeled it with other regression models including the generalized linear model to compare. Results It was shown that the statistical properties of the logarithmic quadratic function model were good even in the early stages of the epidemic, which is generally said to increase exponentially and monotonically. By applying the logarithmic quadratic function model to the data of the number of cases in each country of the world, the starting and the subsiding dates of the epidemic and the total number of cases in each country were estimated. Conclusions Although an epidemic curve in an early period said generally to be exponential, namely linear in the logarithmic space, a quadratic curve regression fits better than the linear and the generalized linear model. These estimates can be informative to reveal the transition mechanism from pre-epidemic to epidemic, and to pandemic.

scholarly journals Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions

2019 ◽  
Vol 6 (12) ◽  
pp. 191227
Author(s):  
Jianhua HU ◽  
Fengwen Zhao ◽  
Qifan Ren ◽  
Ye Kuang ◽  
Tan Zhou ◽  
...  
Keyword(s):  
Pore Size ◽  
Strength Characteristics ◽  
Curing Conditions ◽  
Factors Affecting ◽  
Exponential Functional ◽  
Cemented Backfill ◽  
Small Pore ◽  
Microscopic Features ◽  
Paste Backfill ◽  
Powder Content

Under different exploitive conditions, the humidity levels of the backfill stopes are not the same. Humidity greatly affects the strength and microscopic characterization of the backfill. Cemented paste backfill (CPB) specimens were cured using 0, 30, 70% and standard curing (20°C, 99%) under four different humidity conditions. At 28 days, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques were used to obtain the microscopic features of the CPB specimens. The relationships between the permeability and uniaxial compressive strength (UCS) of the CPB specimens, and the microscopic characteristics of the CPB specimens, were established. The results showed the following: (i) The permeability of the CPB had an exponential functional relationship with its stone powder content. (ii) The stone powder content of CPB and the peak area of the T 2 spectrum are negatively correlated with the UCS. However, there was a T 2 peak area corresponding to the worst UCS with the same stone powder content. (iii) The peak area of the T 2 spectrum showed that the proportion of area of a small pore size was more than 80%, indicating that the pore size was mainly small. The pore diameter of small pores was linearly and inversely proportional to the UCS of the specimens. It can be found that the factors affecting the strength characteristics of CPB include not only the stone powder content, but also the curing conditions of different humidity.

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