Effects of Fine Gangue on Strength, Resistivity, and Microscopic Properties of Cemented Coal Gangue Backfill for Coal Mining

Wang

Advances in Materials Science and Engineering

et al. 2020

Self Cite

Coal gangue-based cemented backfill material (CGCBM) is developed for backfilling the goaf in coal mines. As fresh CGCBM slurry is generally transported into underground openings through a pipeline, and after hardening, it plays the role of supporting the overlying strata. The fluidity, stability, and mechanical (compressive strength) of CGCBM become the most important properties. Adding water-reducing agents (WRAs) is considered to improve the fluidity, stability, and mechanical properties of CGCBM, but there is a risk of increased bleeding. So, two types of WRA (naphthalene series (WRA1) and poly carboxylic acid (WRA2)) are used at different contents (1.0%-2% for WRA1, 0.2%–0.6% for WRA2) by mass of binder. Slump, slump flow, yield stress, and plastic viscosity test are used to evaluate the fluidity properties of CGCBM after adding WRA. Bleeding rate test is used to evaluate the stability of CGCBM after adding WRA. Compressive strength is the most important factor in measuring the mechanical properties. SEM and XRD tests are used to analyse the mechanism of strength change. Results show that the slump, slump flow, and plastic viscosity increase after adding WRA, which reduces the yield stress and improves the fluidity. The bleeding rate increases with the increase of WRA content, leading to a decrease in stability. Adding WRA increases the compressive strength, and it increases first and then decreases with the increase of the content at the later stage. Considering the effects of WRA on the fluidity, stability, and compressive strength properties of CGCBM, the reasonable content of WRA1 and WRA2 is 1.5% and 0.4%, respectively. The research results provide guidance for the design and preparation of CGCBM with favourable performance in practical production.

Section: Introductionmentioning

confidence: 99%

Performance of Coal Gangue‐Based Cemented Backfill Material Modified by Water‐Reducing Agents

Wang

Advances in Materials Science and Engineering

et al. 2020

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“…It has many benefits, such as reducing the accumulation of solid waste, and the occupation of cultivated land, developing and utilizing underground space [2], and protecting groundwater and environment [3]. Cemented gangue backfill material (CGBM), one of the common backfill materials, is made of coal gangue, fly ash, cement, and water [4]. Comparing to other backfill materials, the main raw materials of CGBM, such as coal gangue and fly ash, are plentiful and cheap, and its performance meets the workability and strength requirements of mining.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Diffusion Process of Sulfate Ion in Cemented Gangue Backfill Material

Wang

Advances in Civil Engineering

et al. 2020

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Cemented gangue backfill material (CGBM) is made of coal gangue, fly ash, cement, and water. The backfill body will be corroded by mine water that contains different kinds of corrosive ions. The paper mainly aimed to study the diffusion process of sulfate ion (SO42−) in CGBM. Soluble salt solutions with different concentrations are prepared to simulate various mine water. The SO42− concentration was measured by layered sampling method and chemical analyzing method. The diffusion coefficient was calculated according to the second Fick’s law. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to analyze the degradation mechanisms. The experimental results showed that the SO42− concentration increases in CGBM when the external sulfate solutions concentration increases. With the increasing of magnesium ion (Mg2+) concentration and bicarbonate ion (HCO3−) concentration in the external corrosion solutions, the diffusion coefficient of SO42− was increased, and HCO3− has more significant effects than Mg2+. SO42− reacting with CGBM produced ettringite and gypsum. The ettringite and gypsum changed the pore structure of hardened CGBM and affected the compressive strength of hardened CGBM. Studying the diffusion of SO42− can contribute to predicting the service life of CGBM.

“…Cemented coal waste backfill material (CCWBM), which is an engineered mixture of crushed coal gangue, fly ash, cement, and water, is developed for mine backfilling [8][9][10][11]. All the problems aforesaid can be solved by backfilling CCWBM into the goaf [5,9,12,13].…”

Section: Introductionmentioning

confidence: 99%

The Dosage of Superplasticizer in Cemented Coal Waste Backfill Material Based on Response Surface Methodology

Advances in Materials Science and Engineering

et al. 2019

Self Cite

Cemented coal waste backfill material (CCWBM) is developed for backfilling the goaf in coal mines. As fresh CCWBM slurry is generally transported into underground openings through a pipeline, the fluidity of fresh slurry becomes one of the most important properties. Adding superplasticizer is considered to improve the flow performance of the slurry without alerting the mechanical performance of filling body. e dosage of superplasticizer (SP) is related to filling cost, thus response surface methodology (RSM) is adopted to study the influence of material composition on SP when target slump is 250 mm. e effects of fly ash content, fine gangue ratio, and mass concentration on SP are analyzed using the software of Design-Expert and central composite design (CCD), and models are established for SP. Results show that the SP model coincides greatly with the test results and can be applied to analyze and predict SP in CCWBM. Mass concentration, fly ash content, and fine gangue ratio influence SP from high to low. e interaction of fine gangue ratio and mass concentration between SP is the most significant. e fact that the improved aggregate space model can be applied to analyze the fluidity of CCWBM is proved too. e research results provide guidance for the design and preparation of CCWBM with favourable performance and low cost in practical production.