EAGER: Spherical Porous Reactive Aggregates from Coal Bottom Ash

Drexel University, Philadelphia PA

Investigators

Abstract

This Early-concept Grant for Exploratory Research (EAGER) project pursues research to understand the fundamental physical and chemical mechanisms for producing spherical porous reactive aggregates (SPoRA) for concrete materials using worthless coal bottom ash. Coal power plants around the country generate large volumes of bottom ash with no engineering value and a high environmental cost to the society. This project aims to convert this waste material into value-added reactive aggregates that will improve the cracking resistance of concrete by strengthening the bonding between aggregates and hardened cement. The research will estimate the savings in energy, greenhouse gas emissions, and landfilled waste when using coal bottom ash for construction materials. The project will nurture undergraduate students by incorporating co-op training into this research. Freshman and senior design projects will germinate from this project. Undergraduate students working on this project will serve as mentors for the high school students who are participating in the STEM scholar program of the institution. Residual carbon coal bottom ash is converted to concrete aggregate materials through a sintering process by timing the initiation of volume expansion within the melt trajectory. In parallel to applying thermodynamic and kinetic modeling and experimental synthesizing of SPoRA, will be the benchmarking of its life cycle environmental impacts against conventional lightweight aggregates. The hypothesis is that partially melting the oxide compounds and subsequently combusting the residual carbon will create a porous material encapsulated by a glassy layer that exhibits pozzolanic reactivity. The highly pozzolanic reactive amorphous surface alters the microstructure of the interfacial transition zone, enhancing the cracking resistance of concrete. The dominantly crystalline core of the aggregates provides the strength. The knowledge acquired from creating lightweight aggregates by controlling the amorphous phase as a functional design requirement is transferable to other sintered lightweight aggregates.