Mechanical Transformation of Fly Ash toward Its Utilization in Cemented Paste Backfill

Fly ash (FA) showed low reactivity when being used to prepare the binder for cemented paste backfill (CPB). In the present work, wet-grinding treatment was used to increase the pozzolanic reactivity of FA and promote its sustainable utilization. The results showed that wet-grinding could be a suitable and efficient technology for FA pretreatment. Wet-grinding strongly modified the structure of FA by decreasing the crystalline phase content and the binding energy of Si 2p and Al 2p, contributing to the increase in pozzolanic reactivity of FA. The performance of CPB samples prepared by wet-ground FA was then optimized. This was reflected by the acceleration in the sample setting and increase in the strength development. The compressive strength of the CPB samples prepared by wet-ground FA for 120 min was increased by around 40% after curing for 28 d compared with the control samples.

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Effects of Superplasticizer on the Hydration, Consistency, and Strength Development of Cemented Paste Backfill

Minerals ◽

10.3390/min8090381 ◽

2018 ◽

Vol 8 (9) ◽

pp. 381 ◽

Cited By ~ 31

Author(s):

Jian Zhang ◽

Hongwei Deng ◽

Abbas Taheri ◽

Junren Deng ◽

Bo Ke

Keyword(s):

Underground Mines ◽

Strength Development ◽

Strength Increase ◽

Strengthening Effect ◽

Cemented Paste Backfill ◽

Solid Concentration ◽

Resonance System ◽

Low Field ◽

Binder Ratio ◽

Paste Backfill

The strength and consistency of cemented paste backfill (CPB) are of key concerns in the stope stability and cost control for underground mines. It is common practice to use additives, such as superplasticizer, to improve the performance of CPB. This study mainly focuses on the effects of superplasticizer on the hydration, consistency, and strength of CPB. In this study, a polynaphtalene sulfonate was used as the superplasticizer. The binder is a mix of 33.3% ordinary Portland cement and 66.7% fly ash. The CPB specimens with a tailings-binder ratio of 3:1 and a solid concentration of 70% were then tested by a low field nuclear magnetic resonance system after different hydration times. Effects of polynaphtalene sulfonate on the hydration, fluidity, and strength were investigated. Results showed that the polynaphtalene sulfonate has a strong influence on short-duration hydration, which may contribute to the strength increase of CPB. It has been demonstrated that the polynaphtalene sulfonate improved the fluidity of the CPB mixture. With the increased dosage of polynaphtalene sulfonate, the slump increased. It was also found that the polynaphtalene sulfonate dosage has a negligible effect on the 1 day (d) strength while it has a strengthening effect on the 7 d, 14 d, and 28 d strength of CPB specimens.

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A Binder Prepared by Low-Reactivity Blast Furnace Slags for Cemented Paste Backfill: Influence of Super-Fine Fly Ash and Chemical Additives

SSRN Electronic Journal ◽

10.2139/ssrn.3982069 ◽

2021 ◽

Author(s):

Zhiyun Zhao ◽

Kaihua Guo ◽

Xiangling Wang

Keyword(s):

Blast Furnace ◽

Fly Ash ◽

Cemented Paste Backfill ◽

Chemical Additives ◽

Paste Backfill

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Experimental Investigation on Mechanical Properties of In Situ Cemented Paste Backfill Containing Coal Gangue and Fly Ash

Advances in Civil Engineering ◽

10.1155/2020/7964267 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Xinguo Zhang ◽

Shichuan Zhang

Keyword(s):

Mechanical Properties ◽

Tensile Strength ◽

Fly Ash ◽

Young’S Modulus ◽

Young's Modulus ◽

Friction Angle ◽

Coal Gangue ◽

Cemented Paste Backfill ◽

Paste Backfill

Cemented paste backfill containing coal gangue and fly ash (CGFACPB) is an emerging backfill technique for coal mines that allows environmentally hazardous coal gangue and fly ash to be reused in the underground goaf. Meanwhile, CGFACPB can provide an efficient ground support and reduce the surface subsidence. Due to the difference of consolidation environment between the laboratory and the field, the mechanical properties of the cemented paste backfill vary significantly. In this paper, the core specimens were collected from an underground coal mine where the CGFACPB was used for coal mining, and the mechanical properties of the collected specimens were investigated. The cores were obtained from the underground coal mine, and then the standard cylinders or discs were prepared in laboratory. The uniaxial compressive strength (UCS), Young’s modulus, and Poisson’s ratio were determined by the compression tests, and the tensile strength was achieved by the Brazilian test. Then the internal friction angle and cohesion were calculated using the improved Mohr–Coulomb strength criterion. The results showed the development of UCS can be divided into four stages, and the final long-term stable value was about 5.1 MPa. The development of Young’s modulus had similar trend. Young’s modulus had a range from 550 MPa to 750 MPa and the mean value of 675 MPa. Poisson’s ratio gradually increased with the underground curing duration and eventually approached the stable value of 0.18. The failure type of compression samples was mainly single-sided shear failure. The development of tensile strength can be divided into two stages, and the stable value of the tensile strength was about 1.05 MPa. The development of cohesion can be divided into four stages, and the stable value was about 1.75 MPa. The stable value of the internal friction angle was about 25°. This study can provide significant references for not only the long-term stability evaluation of CGFACPB in the field but also the design of optimal recipe of the cemented paste backfill (CPB).

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Quicklime and Calcium Sulfoaluminate Cement Used as Mineral Accelerators to Improve the Properties of Cemented Paste Backfill with a High Volume of Fly Ash

Materials ◽

10.3390/ma13184018 ◽

2020 ◽

Vol 13 (18) ◽

pp. 4018

Author(s):

Hangxing Ding ◽

Shiyu Zhang

Keyword(s):

Fly Ash ◽

Co2 Emission ◽

Mechanical Performance ◽

High Volume ◽

Hydration Heat ◽

Cemented Paste Backfill ◽

Calcium Sulfoaluminate Cement ◽

Calcium Sulfoaluminate ◽

Paste Backfill ◽

Different Doses

In order to reduce the CO2 emission and cost of binders used in cemented paste backfill (CPB) technology, new blended binders with a large amount of fly ash (FA) were fabricated. Different doses of quicklime and calcium sulfoaluminate cement (CṠA) were used as mineral accelerators to improve the early workability of CPB. The effects of CṠA and quicklime on flowability, compressive strength, pore structure, hydration heat, and hydration evolution were investigated experimentally. The results showed that the addition of quicklime and CṠA reduced the spread diameter of the fresh backfill and improved the mechanical performance of the hardened CPB. With increasing quicklime and CṠA, the cumulative hydration heat of the blended binder distinctly increased in the first 6 h. CṠA improved the initial hydration by increasing the reactivity, and quicklime increased the hydration rate by activating FA. The blended binder (15% quicklime + 10% CṠA) with the lowest CO2 emission and cost had potential application in filling technology.

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