Geo-Technical Characterization of Pond Ash as a Highway Fill Material

Authors : Subhadip Chakraborty.

Volume/Issue : Volume 3 - 2018, Issue 10 - October

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The evolution of mankind has caused overall development of a nation with which there has been an increase in demand of daily utilities. One such increasing demand is of electric power. Though many resources are used for its production, one of the major raw materials is ‘coal’ used for the generation of electricity and outcomes the generation of waste in the form of coal ash is a prerequisite to it. With more than 65 % of India’s electricity capacity generated by thermal power plants, 85% of them use coal as their burning fuel and thus produces a huge quantity of coal ash and its disposal has always been a serious issue of concern for the safety of environment. The coal ash generated is dumped as Pond ash in major portions to disposal site also known as ash pond, located near the plant. Due to use of different type of coal, the properties of Pond ash vary within two thermal power plants and also near the disposal point (inflow) and outflow point within the same ash pond. To assess the feasibility of pond ash as a fill material, pond ash sample was collected from the ash pond situated near the National Thermal power plant in Badarpur, New Delhi. This paper presents a detailed study on the characterization of the Index, geotechnical and chemical properties of pond ash sample. Results reveal that pond ash has Coefficient of uniformity. 5.0 and coefficient of curvature, 1.65. Pond ash shows low specific gravity 2.30 g/cm3 as compared to soil (2.6–2.7 g/cm³), i.e.natural fill material, low amount of unburned carbon content 2.84 % and the maximum dry density is 1.19 g/cm3 and 1.23 g/cm3 whereas optimum moisture content is 28 % and 24.53 % for light and heavy compaction respectively. CBR value for un-soaked sample at light compaction is 9.02% and at heavy compaction is 19.10 % at 2.5 mm penetration. Soaked sample showed a value of 1.34 %. EDXRF test indicates the combined concentration of SiO₂, Al₂O₃ and Fe₂O₃ was 91.85 % and CaO was 0.95%, which verifies it as a Class F category fly ash. The results of chemical analysis indicates that concentration of Arsenic(As), Lead(Pb), Barium(Ba)and Chromium (Cr)are relatively higher than the standard land disposal limit, specified by United States Environment Protect agency (USEPA) TCLP limits for hazardous wastes. So it can be used adequately as embankment and subgrade construction fill material for low-lying areas. Caution must be adopted to prevent contamination of ground water due to the high concentration of some hazardous heavy metals.

Keywords : Pond ash; Fill material; Embankment; Characterization; LOI; ED-XRF.


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