Geotechnical characterization of fly ash composites for backfilling mine voids

Abstract

Backfilling of mine voids is mandatory to avoid subsequent ground stability problems in the form of subsidence. River sand and mill tailings have been widely used since a long time as backfilling materials. However, with a strict regulation banning river sand mining in India, research for developing alternative engineering materials substituting sand has gained importance. In the present study four fly ash composite materials (FCMs) was developed from the fly ash obtained from a captive thermal unit of Rourkela Steel Plant (RSP). The main constituent of the composite were fly ash, lime and gypsum. Detailed physical, and engineering properties were determined for the FCMs. Significant increases in the compressive strength were obtained after 56 days of curing time. A detailed SEM studies was undertaken to account for the increase in strength with time. The fly ash composite developed from RSP has potential to be used as substitute to sand for backfilling the mine voids.

Suitability of Flyash-Lime-Phosphogypsum Composite in Road Pavements

“…Beyond a phosphogypsum content of 2%, the dry unit weight marginally dipped to 12.01 kN/m 3 . Similar observations were reported by [2] where a decrease in dry unit weight of the fly ash-lime mix was observed with the addition of 5% gypsum. …”

“…1. Gamble's slake durability classification Gamble's slake durability classification Variation of predicted and observed(a) slake durability index I(d) 1 and(b) slake durability index I(d) 2 with curing period for the reference mix cured with burlap curing method attributed to the formation of pozzolanic reaction products in the reference mix containing flyash-lime-phosphogypsum. For the flyash-lime-gypsum mixture cured for 28 days for use as base/subbase materials in roads, a medium durable to medium high durable material is required as recommended by [16].…”

“…Addition of lime to the low lime flyash results marginal increase in dry unit weight and optimum moisture content [1]. Addition of gypsum in fly ash mix decreases the dry unit weight of the mix as compared to that without gypsum [2] whereas the optimum moisture content varied from 31.5 to 35.4% and maximum dry unit weight varied from 10.25 to 10.82 kN/m 3 [3]. Standard Proctor tests on the Class F pond ash mixed with varying percentages of lime (4,6, and 10%) and phosphogypsum (0.5, and 1.0%) reported the optimum moisture content and dry unit weight varied from 33.23 to 29.07% and 11.43 to 11.83 kN/m 3 respectively [4].…”

“…The effects of lime content (4, 6, and 10%), gypsum content (0.5 and 1.0%), and curing period (up to 90 days) on the slake durability characteristics of class F fly ash reported that unstabilized fly ash samples and samples stabilized with 4% lime does not even last for first cycle at all the curing periods whereas, additions of small percentages of gypsum (0.5 and 1.0%) in fly ash-lime mixes improved the durability characteristics at 28 days of curing [16]. Slake durability test on the fly ash, lime and gypsum mixes in order to assess the resistance offered by a fly ash mix to weakening and disintegration when subjected to two standard cycles of drying and cooling on specimen cured for 28 and 56 days reported that slake durability index for fly ash mix without gypsum varied from 96% to 97% during the 1st cycle for 28 days cured specimen and increased marginally for 56 days cured specimen [2]. Wetting and drying test on fly ash-lime-gypsum mixes reported no significant reduction in the strength of the fly ash-lime-gypsum mixes even after 20 cycles of wetting and drying [1].…”

Utilization of Circulating Fluidized Bed Combustion Ash and Related Specifications for Mine Backfills

“…광산 채움기술은 광산의 안 전성 향상, 환경영향성 저감, 채굴율 증진을 목적으로 적용되는 기술로서, 종래의 광산 채움기술은 모래, 자갈, 폐석 등의 비활성 물질을 채움재로 사용하거나 시멘트 계 재료와 함께 페이스트화 하여 적용하는 것이 일반적 이다 13) . 최근에는 산업 공정에서 발생하는 다양한 종류 의 무기 폐기물을 채움재로 활용하기 위한 연구가 활발 히 진행되고 있으며, CFBC 석탄재, PCC 석탄재 등을 활용한 채움 기술이 국내·외에서 적극적으로 검토 되고 있다 [15][16][17][18][19] . 그러나 석탄재를 광산 채움 용도로 효 율적으로 활용하기 위해서는 기술적인 검토와 함께 관 련 규격에 대해 향후 충분히 논의를 거쳐야 할 여지가 있다.…”