University of Florida, Ph.D.
EREF Scholar 2018
Beneficial Use of Waste to Energy Ash in Roadway Construction
Chad Spreadbury’s Ph.D. work aims to further expand the beneficial use of waste to energy (WTE) ash as roadway construction aggregates. Beneficial use involves taking a “waste” product and evaluating it from an environmental risk perspective along with assessing its physical properties (e.g., hardness) to determine if and how it may be reused rather than disposed of. This endeavor has global benefits such as landfill diversion and avoidance of greenhouse gas emissions associated with the production and transport of virgin aggregates for construction purposes. Research objectives include examining the physical performance and environmental impacts of utilizing ash-derived aggregate in hot-mix asphalt (HMA) and road base applications, observing the effects of pre-processing on WTE ash-derived aggregate, and investigating the economics of WTE ash recycling.
A common practice in the United States (U.S.) is to comingle bottom ash and fly ash together for disposal, creating a combined ash product. Part of Spreadbury’s Ph.D. work involves screening out coarse (1/4-3/4”) sized combined ash for HMA aggregate and blending 1/4-1.5” combined ash and <1/4” combined ash together to create a road base product. These products will be assessed from a physical and, most importantly, an environmental risk perspective to evaluate the potential for beneficial use of ash-derived aggregates produced from combined ash. The findings from this work may be relevant to any scenario where bottom ash and fly ash are commingled, within or outside the US.
While screening WTE ash can be an acceptable form of preprocessing, washing may also yield additional benefits such as removing lightweight particles (e.g. unburned plastics, wood), which can be detrimental to construction materials. The effect of washing WTE ash to produce an optimal product will also be evaluated in my Ph.D. works, with a particular interest in the wash water created during this process from an environmental standpoint as well as how it may affect the economic feasibility of WTE ash beneficial use.
An economic feasibility assessment of WTE ash as a road construction aggregate is the last component of this research. Spreadbury will investigate the infrastructure necessary for beneficial use beyond a laboratory scale. This analysis will also include needed components to truly assess the economic cost of reuse (e.g., aggregate demand, cost of conventional aggregates, transportation costs) along with how this process may be made more economically feasible (e.g., advanced metals recovery, washing).
Spreadbury began his undergraduate career at St. Petersburg College, FL in Fall 2011 where he received his Associate of Arts degree in Spring 2013 before transferring to the University of Florida (UF) in Fall 2013 to finish his Bachelor of Science degree in Environmental Engineering Sciences in Spring 2016. While at UF, he developed a passion for sustainable solid waste management, which led him to pursue a Ph.D. at UF in Environmental Engineering Sciences. His anticipated graduating in the Spring of 2020.
As a Ph.D., he has had numerous experiences related to sustainable solid waste management through conducting research and providing solutions for parties ranging from local county governments to material/construction contractors to multinational companies. While creating new knowledge is thrilling, he found that sharing it and inspiring others is just as rewarding and exciting. He was first chosen to co-teach Introduction to Engineering, a role in which he walked his students (240/semester) through constructing a landfill, how waste to energy (WTE) facilities work, and how their ash can be beneficially used. He later came full circle when he became the teaching assistant for Solid & Hazardous Waste Management (60 students/semester). He finds delving into the regulatory and professional practice that is so unique to solid waste management that many undergraduates have limited or no previous exposure to has been truly gratifying.