Coal combustion residue as structural fill material for reinforced soil structures

Abstract

Coal combustion residue (CCR) has gained considerable acceptance in civil engineering applications, mainly in the cement industry and brick manufacturing. However, despite an increasing application of CCR, a large proportion remains unutilized globally. This research focuses on the feasibility of using fly ash, bottom ash, and their mixtures as a filling material in reinforced soil structures (RSS). The physical, mechanical characterization of the materials, along with the pullout resistance behavior of the interface between the CCR and a uniaxial polyester geogrid was studied. The grain size distribution tests showed the presence of 80% silt particles in fly ash and 7% in bottom ash. All the CCR samples were non-plastic in nature, and direct shear test results revealed that well compacted CCR samples offer similar shear strength as that of natural soils used as backfill in RSS. The leachability tests of CCR were carried out as per EN 12457–4 (2002) for the assessment of environmental risk. The results revealed that the leachable toxic contents in CCR remained quite below than the standard prescribed limits defined by the European Council Decision 2003/33/EC. The interaction coefficient values for a bottom ash-geogrid interface, obtained from the pullout test, match well with the results of natural/conventional fill material. The interaction coefficient value for the fly ash-geogrid interface was the lowest amongst the materials tested i. e 0.28 at 80 kPa, which is greater than the value recommended by JTJ015-91. The finding of the study demonstrated the suitability of using CCR as an economical, environmentally safe and sustainable structural fill material behind RSS.