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

Abstract

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.

Mechanical Characteristics and Failure Prediction of Cement Mortar with a Sandwich Structure

“…coal mine roof [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Already, many significant results have been obtained.…”

“…The physical and mechanical properties of the cemented composites are influenced, not only by the cementing materials, but also by the structure of the cemented composite. At present, research on goaf treatment mainly focuses on the development and selection of filling materials, mechanical properties of filling materials and surrounding rock, and evaluation and control of the stability of the coal mine roof [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Already, many significant results have been obtained.…”

“…Already, many significant results have been obtained. For example, Zhao et al studied the application of slag cement and fly ash for strength development in cemented paste backfills, and found that the mix designs "3% slag-blended cement" and "2.5% slag-blended cement +2-2.5% fly ash" satisfied the 700 kPa strength threshold required for slope stability [13]. Wang et al applied the coal mine roof rating (CMRR) to evaluate the roof stability of coal mines in China and found that the CMRR guidelines are useful to preliminarily investigate stability in Panjiang Coal Field mines [16].…”

Vertical Stress and Deformation Characteristics of Roadside Backfilling Body in Gob-Side Entry for Thick Coal Seams with Different Pre-Split Angles

“…In China, backfilling mining has made great achievements, including gangue backfilling material, cemented paste material and high-water-content materials [1][2][3][4]. Meanwhile, retained gob-side entry (RGE) is a significant development for longwall mining without leaving gate pillar unmined.…”

Experimental Research on Deformation Characteristics of Waste-Rock Material in Underground Backfill Mining

“…In recent years, backfill mining methods have developed rapidly around the world [1][2][3][4], among which waste-rock backfill mining has become increasingly popular in the Chinese coal mining industry [5][6][7]. This method not only protects surface buildings, but also reduces environmental pollution caused by the large quantities of waste-rock material produced during roadway excavations and coal washing [8][9][10][11][12].…”