Title: An economic feasibility model for ash use in flowable fill with integration of logistics and contaminant leaching factors

Authors: Rajender Gaddam, Hilary I. Inyang, David T. Young, Emem Umoh

Addresses: Water Resources Engineer, Dewberry, 6135 Lakeview Road – Suite 400, Charlotte, NC 28269, USA. ' Global Institute for Energy and Environmental Systems (GIEES), University of North Carolina, 9201 University City Boulevard, Charlotte, NC 28223, USA. ' Department of Civil Engineering, University of North Carolina, 9201 University City Boulevard, Charlotte, NC 28223, USA. ' Global Institute for Energy and Environmental Systems (GIEES), Department of Civil Engineering, University of North Carolina, 9201 University City Boulevard, Charlotte, NC 28223, USA

Abstract: Encasement of utility cables and pipes in flowable fill monoliths formed in trenches requires the use of materials that satisfy both strength and contaminant leachability limits. Coal combustion ash is often readily available for use in flowable fill construction. The use of ash in desirably large quantities, calls for the determination and selection of the maximum ash mix fraction that meets strength requirements for excavatability and contaminant leachability. Initial economic feasibility assessments can then be performed in terms of the costs and revenues of installing flowable fill using the ash mix fraction selected. In this paper, the methodology is demonstrated by testing monoliths of flowable fill containing 0–20% (by weight) of coal combustion fly ash for Unconfined Compressive Strength (UCS) and leachability indices, L_i values of selenium and arsenic. It was found that the monolith containing 20% by weight of ash satisfied the excavatable fill maximum strength requirements of 2070 N/m², and selenium and arsenic minimum L_i values of 17.0 and 14.0, respectively. An economic feasibility estimation methodology is presented to relate ash sale revenues and flowable fill placement costs for various mix fractions of ash.

Keywords: flowable fill; fly ash; contaminant leaching; controlled low strength material; CLSM; economic feasibility; logistics; utility cables; utility pipes; leachability; coal combustion ash; waste management; environment; environmental assessment.

DOI: 10.1504/IJEWM.2006.011123

International Journal of Environment and Waste Management, 2006 Vol.1 No.1, pp.20 - 38

Published online: 17 Oct 2006 *

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