Water Repellency for Ash Containment and Reuse

Investigators: University of North Carolina Charlotte

Start Date:
Jul 2014

Award Amount:

In the U.S., more electricity is derived from coal (40% in 2012) than any other source. Notwithstanding major changes in the industry, coal use actually outpaced natural gas during the first quarter of 2013, according to the Energy Information Administration. As a result, 130.2 million short tons of coal combustion residuals (CCR) were produced in 2010, with a 37.9% reuse rate, as compiled by the American Coal Ash Association. Of the CCR types (fly ash, bottom ash, slag, FGD gypsum, etc.) fly ash, by far, is produced in the greatest amount (67 million short tons in 2010). Even if coal combustion ceased today, past generation means that there would still be several billion tons of ash distributed in various impoundments; facilities which, because of recent regulatory changes, are all in the process of being closed. These same regulations are also in the process of eliminating the second largest category for re-use: structural fills and embankments (4.7 million short tons in 2010). This project will provide data to support the use of an innovative approach to render fly ash water repellent, thereby increasing the fraction which can be re-used rather than landfilled. Even if landfilled, water repellency may serve as an alternative, lower-cost barrier to infiltration and leachate. In terms of EREF’s strategic plan, this project provides an opportunity to expand its group of stakeholders to include electric utilities while addressing the following EREF Research Areas of Specialization: 1) Landfills (i.e., covers, environmental protection and waste pre-treatment) and 5) Combustion/Waste-to-energy (i.e., alternative waste streams/special wastes).

The objectives of this project may be summarized as:

  1. Determine laboratory-based relationships between water repellency, breakthrough head, wetting/drying hysteresis, hydraulic conductivity and shear strength in compacted ash.
  2. Determine the extent to which infiltration can be modeled in compacted ash fills and embankments as a function of water repellency.