Because of stringent environmental regulations, the power generation industry must take measures to reduce the emission of nitrogen oxides (NOx), sulfur oxides (Sox), and mercury (Hg). Low-NOx burners reduce emissions by changing the combustion characteristics of coal boilers, but they increase the amount of residual unburned carbon in the fly ash. Increased carbon levels in fly ash make air-entrained concrete production more difficult, because the activated carbon absorbs the desired air-entraining admixture in the concrete. As a result, most high-carbon-content fly ash has to be landfilled, resulting in significant land purchase costs and potential environmental issues. This project will develop technology for using this fly ash as a base course for asphalt pavements. Unlike concrete, which needs air voids, minimal air void content is preferred for the asphalt application. In Phase I, laboratory tests were conducted to evaluate the performance of recycled asphalt treated with cementitious high-carbon fly ash. The test results indicated that the high-carbon fly ash could be used as a quality base course material for asphalt pavement. In Phase II, three test cells, each 500 feet long, will be built and subjected to accelerated traffic loads to compare the performance of fly-ash-treated recycled asphalt to that of conventional crushed aggregate, and to untreated recycled asphalt pavement. An economic analysis will be conducted to evaluate the cost-effectiveness of the material.
Commercial Applications and Other Benefits as described by the awardee: The technology offers the potential to use one hundred percent of the cementitous high carbon fly ash that otherwise would be landfilled, eliminating the costs of disposing and landfilling. Both the power industry and the highway industry should benefit from significant savings in cost and energy.
