Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

Niroshan, Naguleswaran; Yin, Ling; Sivakugan, Nagaratnam; Veenstra, Ryan

doi:10.1007/s10706-018-0455-5

Cited by 23 publications

(7 citation statements)

References 25 publications

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“…To determine the various types of hydration products inside the filled objects for different curing times of 3 and 7 days and how their contents varied, EDS spot element testing was performed on the filled objects for a curing time of 7 days under 1000× magnification and EDS surface element testing was performed on the filled objects for curing times of 3 and 7 days. The results obtained by observing the filled objects for curing times of 3 and 7 days using SEM show that the hydration products of the filled objects are primarily comprised of randomly distributed amorphous flocculent tobermorite as well as interlaced fiber-like and needle/rod-like ettringite [19,34]. Upon increasing the curing time from 3 to 7 days, the hydration reaction persisted as indicated by the gradual decrease in the abundance of needle-like hydration products and the gradual increase in the abundance of flocculent hydration products.…”

Section: Results Of Energy Dispersive Spectrometer (Eds) Analysismentioning

confidence: 99%

Influential Factors in Transportation and Mechanical Properties of Aeolian Sand-Based Cemented Filling Material

Zhou

Ouyang

et al. 2019

Minerals

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Given that normal filling technology generally cannot be used for mining in the western part of China, as it has only a few sources for filling gangue, the feasibility of instead using cemented filling materials with aeolian sand as the aggregate is discussed in this study. We used laboratory tests to study how the fly ash (FA) content, cement content, lime–slag (LS) content, and concentration influence the transportation and mechanical properties of aeolian-sand-based cemented filling material. The internal microstructures and distributions of the elements in filled objects for curing times of 3 and 7 days are analyzed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The experimental results show that: (i) the bleeding rate and slump of the filling-material slurry decrease gradually as the fly ash content, cement content, lime–slag content, and concentration increase, (ii) while the mechanical properties of the filled object increase. The optimal proportions for the aeolian sand-based cemented filling material include a concentration of 76%, a fly ash content of 47.5%, a cement content of 12.5%, a lime–slag content of 5%, and an aeolian sand content of 35%. The SEM observations show that the needle/rod-like ettringite (AFt) and amorphous and flocculent tobermorite (C-S-H) gel are the main early hydration products of a filled object with the above specific proportions. After increasing the curing time from 3 to 7 days, the AFt content decreases gradually, while the C-S-H content and the compactness increase.

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Section: Results Of Energy Dispersive Spectrometer (Eds) Analysismentioning

confidence: 99%

Influential Factors in Transportation and Mechanical Properties of Aeolian Sand-Based Cemented Filling Material

Zhou

Ouyang

et al. 2019

Minerals

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“…With the presence of water, tailings, and calcium-rich binders such as MC, the primary hydration reaction is strongly time-dependent [27,29,48]. The major hydration products are Calcium-Silicate-Hydrates (C-S-H), in the form of poorly crystalline fibres to the reticular network; Calcium hydroxide (Ca(OH)2), in the form of hexagonalprism crystals; and ettringite (AFt), in the form of needle-shaped prismatic crystals, which encourage solidification and flocculation of the tailings particles and, hence, enhance strength performance [29,[49][50][51][52]. Under the influence of applied stress during curing, the microstructure of sample A3.6T7 in Figure 8b contains much smaller and far fewer pores or cracks.…”

Section: Sem Observationsmentioning

confidence: 99%

The Effect of Curing under Applied Stress on the Mechanical Performance of Cement Paste Backfill

et al. 2021

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After placing the Cement Paste Backfill (CPB) slurry in mined cavities underground, during the setting and hardening processes, the weight and hydrostatic pressure of the upper-layer CPB slurry applies an axial load over the bottom-layer CPB materials, which is called the self-consolidation of CPB slurry. Due to this phenomenon, the mechanical properties of in situ CPB could be considerably different from laboratory results. Hence, it is crucial to understand the effect of self-consolidation behaviour on the mechanical properties of backfill material. This paper presents an experimental study on the impact of axial applied stress (As) during curing, which represents the various self-consolidation conditions and curing times on the mechanical properties of CPB material prepared using the tailings of a copper mine in South Australia and a newly released commercially manufactured cement called Minecem (MC). A curing under pressure apparatus (CPA) is designed to cure CPB samples under axial applied stress. The equipment can apply and measure axial load during curing and measure the passive lateral stress due to axial load which represents the horizontal stresses at a certain depth of CPB stope on the retaining structure. The prepared samples with axially applied pressure during curing were tested under uniaxial and triaxial compressive loading conditions. Microstructural tests by scanning electron microscopy (SEM) were also used to study the fabric evolution in response to various applied stresses during curing. Overall, the increase in As during curing leads to higher resultant CPB peak strength and stiffness under uniaxial and triaxial compression tests. For instance, a sample cured under 3.6 MPa axial load for 28 days demonstrates a uniaxial compressive strength (UCS) value of five times more than a sample cured under atmospheric curing conditions. Passive lateral stress was measured during the curing period and was representative of underground barricade stress. Furthermore, during curing, the axial applied stress changed the initial CPB pore structure after placement. With the increase in applied stress, the stress compressed CPB samples at the macroscale, leading to much smaller pores or cracks prior to the hydration process. At an early stage, the increase in UCS due to axial applied stress mainly arises from a dense microstructure caused by the compression of tailings and cement particles. With the increase in curing time, the observation also shows that a CPB matrix with fewer pore spaces may improve the hydration progress; hence, the influence of axial applied stress becomes more pronounced in long-term UCS.

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“…This technology can control the depth of the bottom plate damage and can play a better role in groundwater resources [27][28][29][30]. The protective effect of the coal mine, especially under the condition of coal mining under confined water, can significantly improve the safe production conditions of coal mines [31][32][33][34]. Furthermore, this technology can effectively control the surface subsidence and deformation to achieve nonrelocation of coal mining, which can greatly improve coal resources.…”

Section: Introductionmentioning

confidence: 99%

Control of Water Inrush from Longwall Floor Aquifers Using a Division Paste Backfilling Method

Chang

Yao

et al. 2021

Geofluids

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Aiming at the problem of the safety mining problems of longwall paste filling working face under buildings on high confined water in the Daizhuang Coal Mine, the paste filling mining method was used. A series of theoretical analyses, numerical simulations, and field measurements were applied. The results showed that when the filling interval of the working face increases from 1.2 m to 3.6 m, no significant change is found in the depth of the perforated plastic zone of the floor strata. According to the types of water-conducting cracks in the floor strata of the working face 11607, the floor strata are divided into the floor intact area, the structure developed area, and the floor weak area. Based on that, the measures for preventing and controlling the floor failure in the paste filling working face are proposed. Furthermore, the failure depth of the floor of the test working face was detected by the on-site water injection method, and the results showed that the maximum failure depth of the floor of the test working face was about 3 m.

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Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

Cited by 23 publications

References 25 publications

Influential Factors in Transportation and Mechanical Properties of Aeolian Sand-Based Cemented Filling Material

Influential Factors in Transportation and Mechanical Properties of Aeolian Sand-Based Cemented Filling Material

The Effect of Curing under Applied Stress on the Mechanical Performance of Cement Paste Backfill

Control of Water Inrush from Longwall Floor Aquifers Using a Division Paste Backfilling Method

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