Measurement and Stabilization of Waste-to-Energy Ash−Concrete Expansion in Seawater

Combustion residues from waste-to-energy systems can be stabilized with portland cement to form offshore artificial reefs that augment fishing harvests. To use secondary raw materials from waste-to-energy systems for beneficial applications, the stabilized material must maintain its structural integrity in a marine environment. The current study compared the rates of expansion of ash−concrete with selected combinations of bottom ash and/or scrubber residue, examined changes in mineral phases during exposure to seawater, and assessed mechanisms for reducing expansion. The rate of expansion of ash−concrete prepared with bottom ash alone or with scrubber residue was approximately 1.5 times the rate of expansion of mortar. Superficial structural degradation of these materials in seawater was not observed. Ash−concrete prepared with scrubber residue alone exhibited significant expansion and structural deterioration after 80 days of exposure. Bubbling in ash−concrete with scrubber residue provided physical evidence of gas formation. Hydrating scrubber residue at a moisture content of 30% for 5 days prior to stabilization reduced expansion by a factor of 3 and mitigated bubbling and cracking 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 residue may limit expansion by facilitating the formation of gypsum and ettringite and the liberation of gas prior to stabilization.