Measurement and stabilization of waste-to-energy ash - Concrete expansion in seawater

Combustion residues from waste-to-energy systems can be stabilized with por tland cement to form offshore artificial reefs that augment fishing harvest s. To use secondary raw materials from waste-to-energy systems for benefici al applications, the stabilized material must maintain its structural integ rity in a marine environment. The current study compared the rates of expan sion of ash-concrete with selected combinations of bottom ash and/or scrubb er residue, examined changes in mineral phases during exposure to seawater, acid assessed mechanisms for reducing expansion. The rate of expansion of ash-concrete prepared with bottom ash alone or with scrubber residue was ap proximately 1.5 times the rate of expansion of mortar. Superficial structur al degradation of these materials in seawater was not observed. Ash-concret e prepared with scrubber residue alone exhibited significant expansion and structural deterioration after 80 days of exposure. Bubbling in ash-concret e with scrubber residue provided physical evidence of gas formation. Hydrat ing scrubber residue at a moisture content of 30% for 5 days prior to stabi lization reduced expansion by a factor of 3 and mitigated bubbling and crac king that was observed in ash-concretes with scrubber residue. Ettringite, associated with expansion of conventional concrete, was present in hydrated scrubber residue but not in scrubber residue. Hydrating the scrubber resid ue may limit expansion by facilitating the formation of gypsum and ettringi te and the liberation of gas prior to stabilization.