Application of Slag–Cement and Fly Ash for Strength Development in Cemented Paste Backfills

The present study investigates the combined capacity of a newly developed slag-blended cement (MC) and fly ash (FA) as a sustainable solution towards improving the mechanical performance of the cemented paste backfill (CPB) system of a copper-gold underground mine. A total of thirteen mix designs consisting of three MC-treated and ten MC + FA-treated blends were examined. Samples were prepared with a solids content of 77% (by total mass), and were allowed to cure for 7, 14, 28, 56 and 128 days prior unconfined compression testing. Scanning electron microscopy (SEM) studies were also carried out to observe the evolution of fabric in response to MC and MC + FA amendments. The greater the MC content and/or the longer the curing period, the higher the developed strength, toughness and stiffness. The exhibited improvements, however, were only notable up to 56 days of curing, beyond of which the effect of curing was marginal. The performance of 4% Portland cement or PC (by total dry mass) was found to be similar to that of 1.5% MC, while the higher MC inclusions of 2.5% and 3%, though lower in terms of binder content, unanimously outperformed 4% PC. The use of FA alongside MC improved the bonding/connection interface generated between the tailings aggregates, and thus led to improved mechanical performance compared with similar MC inclusions containing no FA. Common strength criteria for CPBs were considered to assess the applicability of the newly introduced MC and MC + FA mix designs. The mix designs “3% MC” and “2.5% MC + 2–2.5% FA” satisfied the 700 kPa strength threshold required for stope stability, and thus were deemed as optimum design choices.

Download Full-text

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.

Download Full-text

Strength development and microstructural investigation of lead-zinc mill tailings based paste backfill with fly ash as alternative binder

Cement and Concrete Composites ◽

10.1016/j.cemconcomp.2020.103553 ◽

2020 ◽

Vol 109 ◽

pp. 103553 ◽

Cited By ~ 5

Author(s):

S.K. Behera ◽

C.N. Ghosh ◽

D.P. Mishra ◽

Prashant Singh ◽

K. Mishra ◽

...

Keyword(s):

Fly Ash ◽

Strength Development ◽

Microstructural Investigation ◽

Mill Tailings ◽

Paste Backfill ◽

Lead Zinc

Download Full-text

Mechanical Performance of Confined Consolidation on the Strength Development of Cemented Paste Backfill

Geotechnical and Geological Engineering ◽

10.1007/s10706-019-01074-x ◽

2019 ◽

Vol 38 (2) ◽

pp. 1097-1110

Author(s):

Chao Yang ◽

Peng Yang ◽

Wen-sheng Lv ◽

Zhi-kai Wang

Keyword(s):

Mechanical Performance ◽

Strength Development ◽

Cemented Paste Backfill ◽

Paste Backfill

Download Full-text

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

Advances in Civil Engineering ◽

10.1155/2021/5492272 ◽

2021 ◽

Vol 2021 ◽

pp. 1-15

Author(s):

Haijun Wang ◽

Yun Duan

Keyword(s):

Fly Ash ◽

Strength Development ◽

Sustainable Utilization ◽

Cemented Paste Backfill ◽

Efficient Technology ◽

Pozzolanic Reactivity ◽

Wet Grinding ◽

Paste Backfill ◽

Mechanical Transformation ◽

Wet Ground

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.

Download Full-text

Prediction of compressive strength development for blended cement mortar considering fly ash fineness and replacement ratio

Construction and Building Materials ◽

10.1016/j.conbuildmat.2020.121532 ◽

2020 ◽

pp. 121532

Author(s):

Y. Sun ◽

K.Q Wang ◽

H.S. Lee

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Cement Mortar ◽

Blended Cement ◽

Strength Development ◽

Replacement Ratio ◽

Compressive Strength Development

Download Full-text

Early-age strength development in fly ash blended cement composites: investigation through chemical activation

Magazine of Concrete Research ◽

10.1680/jmacr.17.00336 ◽

2019 ◽

Vol 71 (5) ◽

pp. 260-270 ◽

Cited By ~ 7

Author(s):

T. Hemalatha ◽

Saptarshi Sasmal

Keyword(s):

Fly Ash ◽

Chemical Activation ◽

Blended Cement ◽

Strength Development ◽

Early Age ◽

Cement Composites

Download Full-text

The effects of seawater and nanosilica on the performance of blended cements and composites

Applied Nanoscience ◽

10.1007/s13204-020-01328-8 ◽

2020 ◽

Vol 10 (12) ◽

pp. 5009-5026 ◽

Cited By ~ 6

Author(s):

Pawel Sikora ◽

Didier Lootens ◽

Maxime Liard ◽

Dietmar Stephan

Keyword(s):

Transport Properties ◽

Reaction Rate ◽

Mechanical Performance ◽

Setting Time ◽

Blended Cement ◽

Heat Of Hydration ◽

Strength Development ◽

Cement Pastes ◽

Blended Cements ◽

Setting Times

AbstractThis study investigates the effects of seawater and nanosilica (3% by weight of cement), on the fresh and hardened properties of cement pastes and mortars produced with two types of low heat cements: Portland pozzolana cement (CEM II) and blast furnace cement (CEM III). The heat of hydration, initial and final setting times, rheological properties, strength development, sorptivity and water accessible porosity of the cement pastes and mortars were determined. The data reveal that cement type has a significant effect on the reaction rate of cement with seawater and nanosilica (NS). Specimens produced with slag-blended cement exhibited a higher cement reaction rate and the composite produced exhibited better mechanical performance, as a result of the additional reaction of alumina rich phases in slag, with seawater. Replacement of freshwater with seawater contributes mostly to a significant improvement of early strength. However, in the case of slag-blended cement, 28 day strength also improved. The incorporation of NS results in additional acceleration of hydration processes, as well as to a decrease in cement setting time. In contrast, the addition of NS results in a noticeable increment in the yield-stress of pastes, with this effect being pronounced when NS is mixed along with seawater. Moreover, the use of seawater and NS has a beneficial effect on microstructure refinement, thus improving the transport properties of cement mortars. Overall, the study has showed that both seawater and NS can be successfully used to accelerate the hydration process of low heat blended cements and to improve the mechanical and transport properties of cement-based composites.

Download Full-text

Reactivity of Fly Ash At High pH

MRS Proceedings ◽

10.1557/proc-178-139 ◽

1989 ◽

Vol 178 ◽

Cited By ~ 22

Author(s):

Hans S. Pietersen ◽

Alex L. A. Fraay ◽

Jan M. Bijen

Keyword(s):

Particle Size ◽

Fly Ash ◽

Glass Structure ◽

Blended Cement ◽

Dissolution Kinetics ◽

Strength Development ◽

Density Fractions ◽

Show Evidence ◽

The Many ◽

Class F Fly Ash

AbstractThe reactivity of fly ash in cementituous systems has been an object of many studies, and is only understood in broad terms. It is generally agreed that the particle size distribution of fly ash correlates with strength development. It has also been demonstrated that temperature and pH development of the blended cement paste have an effect on fly ash reactivity. It is however not clear whether ash chemistry and/or ash glass structure have an influence on its reactivity, as is the case with some blast furnace slag cements. In order to discriminate between the many variables controlling fly ash reactivity, the dissolution kinetics of class-F fly ash have been studied. The fly ash was first separated into equal size and density fractions. These were reacted with NaOH, with a pH ranging from 13.0 to 13.7 and temperatures between 20 and 40°C. If the results of the dissolution experiments are corrected for differences in glass content and particle size, the effects of temperature and pH seem to be of more importance than differences in ash chemistry. The dissolution proceeded virtually congruent. TEM micrographs of some of the ash fractions indicate that a wide variety of glasses may be encountered in fly ashes; most glasses show evidence of phase separation. The results are discussed with respect to glass structure and glass dissolution-theory.

Download Full-text