scholarly journals Effect of Gypsum Addition on the Mechanical and Microstructural Performance of Sulphide-Rich Cemented Paste Backfill

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 283
Author(s):  
Yu Tang ◽  
Juanrong Zheng ◽  
Lijie Guo ◽  
Yue Zhao
Keyword(s):  
Mechanical Performance ◽  
Early Stage ◽  
Mineralogical Composition ◽  
Strength Loss ◽  
Cemented Paste Backfill ◽  
X Ray Diffraction ◽  
Granulated Blast Furnace Slag ◽  
Paste Backfill ◽  
Sulphide Tailings ◽  
Activated Slag

The present study investigates the effect of β-hemihydrate gypsum (HG) dosages on the mechanical and microstructural performance of cemented paste backfill (CPB) produced from sulphide-rich mine tailings using NaOH-activated slag (NAS) as the major binder. X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analyses were carried out to elucidate the mineralogical composition and microstructure of NAS-HG-CPB samples. The results illustrate that the main hydration products of NAS-HG-CPB from sulphide-rich tailings are crystalline (CaSO4•2H2O and ettringite (AFt), 3CaO•Al2O3•3CaSO4•32H2O) and amorphous. The results also show that the 28 d unconfined compressive strength (UCS) of CPB with 30 wt. % HG replacing NAS increased by 52% compared to the UCS of CPB containing no HG, and both have stable long-stage (180 d) UCS (i.e., no strength loss). Excess HG addition (≧50 wt. %) reduced the early-stage (≦28 d) UCS of NAS-HG-CPB and led to unstable long-stage (180 d) UCS by the formation of secondary gypsum. The use of 30 wt. % HG replacing NAS in NAS-HG-CPB accelerates the hydration process of ground granulated blast furnace slag (GGBS) in the alkaline solution by forming ettringite (AFt), leading to the denser microstructure and improved mechanical performance in comparison with CPB containing no HG. The NAS-HG binder with low dosages of HG (≦30 wt. %) will be a promising binder for stabilising sulphide and non-sulphide tailings and CPB production.

scholarly journals Strengthening Behavior of Cemented Paste Backfill Using Alkali-Activated Slag Binders and Bottom Ash Based on the Response Surface Method

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 855
Author(s):  
Qi Sun ◽  
Xueda Wei ◽  
Tianlong Li ◽  
Lu Zhang
Keyword(s):  
Response Surface ◽  
Bottom Ash ◽  
Hydration Product ◽  
Cemented Paste Backfill ◽  
Alkali Activated Slag ◽  
Surface Method ◽  
Optimal Mix ◽  
Paste Backfill ◽  
Activated Slag ◽  
Alkali Activated

A new type of cemented paste backfill (CPB) was prepared by using the bottom ash (BA) from a thermal power plant as an aggregate, alkali-activated slag as a binder, and an air-entraining agent as an admixture. Based on the central composite design (CCD) response surface method, the mix ratio was optimized, and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was performed on the optimal mix ratio. ImageJ software was utilized to determine the porosity of the experimental samples at various curing ages. The results indicate that the optimal mix ratio of the aggregate-binder ratio is 3.28, the alkali dosage is 3%, the solid content is 67.44%, and the air-entraining agent dosage is 0.1%. As the curing age increases, the porosity of CPB gradually decreases. A calcium aluminosilicate hydrate (C-A-S-H) gel is the main hydration product of alkali-activated slag. At the beginning of the hydration reaction, the slag gradually dissolves, and the C-A-S-H product binds the BA together. At 14 d, complete calcium hydroxide (CH) crystals appeared in the hydration product. Finally, the degree of C-A-S-H crystallization increased further to form a dense structure.

scholarly journals 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 ◽  
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.

scholarly journals Study on Microstructural Evolution and Strength Growth and Fracture Mechanism of Cemented Paste Backfill

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
Jian-Xin Fu ◽  
Wei-Dong Song ◽  
Yu-Ye Tan
Keyword(s):  
Residual Strength ◽  
Mass Fraction ◽  
Solid Phase ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Cemented Paste Backfill ◽  
X Ray Diffraction ◽  
Pressure Peak ◽  
Paste Backfill ◽  
Curing Age

The relations among the uniaxial compressive strength of cemented paste backfill (CPB) with solid phase mass fraction, cement sand ratio, and curing age were studied. The UCS of CPB samples increased exponentially with the increase of solid phase mass fraction and curing age but increased linearly with the increase of cement sand ratio. The results of X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that the strength was determined by the amount of ettringite and C-S-H gelling. With the increase of ettringite and C-S-H gelling, the strength became larger. The triaxial compression test was conducted by selecting four kinds of CPB samples. The results showed that, with the increase of confining pressure, peak and residual strength became larger, but the elastic modulus decreased. When the ratio of confining pressure and uniaxial strength is about 1 : 2, the CPB samples show significant ductility characteristics and the ratio of residual strength and peak strength increased obviously.

scholarly journals Low-Carbon Binder for Cemented Paste Backfill: Flowability, Strength and Leaching Characteristics

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 707 ◽  
Author(s):  
Jingping Qiu ◽  
Yingliang Zhao ◽  
Hui Long ◽  
Zhenbang Guo ◽  
Jun Xing ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Orthogonal Experiment ◽  
Solid Content ◽  
Raw Material ◽  
Cemented Paste Backfill ◽  
Low Carbon ◽  
Optimum Parameters ◽  
Paste Backfill ◽  
Activated Slag ◽  
Furnace Slag

Blast furnace slag was used as the main raw material to prepare the alkali activated slag (AAS), a low-carbon binder, for cemented paste backfill (CPB). The optimum parameters for preparing the AAS binders using an orthogonal experiment were obtained. Under the optimum conditions (NaOH content was 3 wt. %, Ordinary Portland cement (OPC) content was 7 wt. %, and gypsum dosage was 4 wt. %), the 28 days compressive strength of the binder was 29.55 MPa. The flow ability of the fresh CPB slurry decreased with solid content due to the increased yield stress, while the flow ability increased when rising the binder dosage. A predictive model for the compressive strength of CPB samples was reached through multivariate analysis and the R2 values were higher than 0.9. Sensitivity analysis showed that the solid content is the most important parameter which influences on the development of the CPB strength with a correlation coefficient of 0.826. From the Toxicity Characteristic Leaching Procedure (TCLP) tests, the leaching concentrations of Pb and Cd were below the threshold. As a result, the AAS has potential application as an alternative binder and cemented paste backfill.

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.

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