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- MakaleYalnız künye2021Sodium silicate effect on setting properties, strength behavior and microstructure of cemented coal fly ash backfill
Cavusoglu, Ibrahim; Yilmaz, Erol; Yilmaz, Ali Osman
Representing an engineered mixture of coal fly ash, cement and water, cemented coal fly ash backfill (CCB) is typically employed for filling the openings created after coal excavation in the earth. A high rate of productivity for coal mines requires a high early-age strength backfill design. Therefore, the use of admixtures in CCB is key for accelerating the backfill setting time and augmenting short-and long-term strength. This study offers the effect of sodium silicate (SS) as an accelerator on early age mechanical and microstructure properties of CCB. SS-based admixture was used for a dosage of 0.5, 1 and 1.5 wt% in CCB that contains 25 wt% ordinary Portland cement OPC and 75 wt% coal fly ash. Backfill setting time was done by using the Vicat system while its strength and pore structure were measured by using the uniaxial compressive strength test, and scanning electron microscopy and Hg intrusion porosimetry. Results display that use of SS in CCB increases its short-term strength gain up to 14% and shortens the mining cycle by cutting its setting time up to 58%. The microstructure analyses also indicate that CCB formulated with SS has a finer pore structure than that without admixture. The outcomes of the present study will be advantageous to evaluate both setting time and strength behavior of CCB used in coal mines, thereby causing the effective backfill plan in terms of money saving and easy operation.
- MakaleYalnız künye2021Additivity effect on properties of cemented coal fly ash backfill containing water-reducing admixtures
Cavusoglu, Ibrahim; Yilmaz, Erol; Yilmaz, Ali Osman
Cemented coal fly ash backfill (CCB), a flowable structure of coal fly ash, binding agent and mixing water, has been often employed in mining operations to offer ground support as well as waste disposal solutions. An appropriate CCB mass should have sufficient rheological (e.g., workability) and mechanical (e.g., strength and stability) characteristics. Chemical admixtures are well known to greatly enhance the pumpability and strength properties of cementitious materials. Thus, this work provides the effect of water-reducing admixtures (namely, Sikament MR 50 W and Sikament FFN) on characteristics of CCB materials manufactured at a constant slump value. The role of admixtures in CCB mix is to reduce the cement-related costs, to modify the properties of the hardened backfills, and to ensure the quality of the backfill during mixing, transporting, placing, and curing. These admixtures were used at a dosage of 1% and 2% by weight of anhydrous material on cement. Several laboratory tests including slump, setting time, uniaxial compressive strength, scanning electron microscopy and mercury intrusion porosimetry were undertaken on CCB samples to understand their fresh and hardened performance. Experimental results show that the admixtures used ensure the slump required to deliver CCB at low water/cement ratios, improve short- and long-term backfill strengths up to 33%, and decrease the total porosity of the tested CCB. The findings of this study also show that the admixture use in CCB leads to a significant decrease in the considered cement content and a remarkable increase in the mechanical strength. As a result, understanding the actual fresh and hardened properties of CCB remains crucial for the choice of the greatest acting backfill admixture and for a fruitful change from capable experimental results to the in-situ conditions.