Performance of structural concrete using Waste-to-Energy (WTE) combined ash

By Yixi Tian*, A.C. (Thanos) Bourtsalas*, Shiho Kawashima, Siwei Ma, Nickolas J. Themelis

Journal: Waste Management Volume 118 (December 2020), Pages 180–189

Department of Earth and Environmental Engineering
Fu Foundation School of Engineering & Applied Science
Columbia University

The study was supported by the Earth Engineering Center of Columbia University and Global WtERT Council, Inc. The authors gratefully acknowledge the contribution of the engineers of Covanta for the sample collection.


• This study assessed the use of US WTE residues for raw materials savings.
• Up to 100 wt% of aggregate in concrete can be substituted by combined ash > 2 mm.
• Combined ash < 2 mm is not suitable as sand substitute due to metallic aluminum.
• The compressive strength of optimal products exceeds 28 MPa after 28-day curing.
• Optimal products can be used in construction and comply with leaching standards.


In the U.S., about 27 million metric tons of municipal solid waste are used as fuel in Waste-to-Energy (WTE) power plants, generating about seven million tons of mixed bottom ash and fly ash (combined ash) annually, which are disposed of in landfills after metal separation. This study assessed the effect of using combined ash as a substitute of mined stone aggregates on the mechanical properties and leachability of cement mortar and concrete. The as-received combined ash was separated into three fractions: fine (<2 mm), medium (2–9.5 mm), and coarse (9.5–25 mm). The substitution of up to 100% of stone aggregate by the coarse and medium fractions of combined ash produced concrete with compressive strength exceeding 28 MPa after 28 days of curing. Similar results were obtained when the fine combined ash was used as a sand substitute, at 10 wt%, in mortar. The concrete specimens were subjected to several days of curing and mechanical testing. The results were comparable to the properties of commercial concrete products. The mechanical test results were supplemented by XRD and SEM analysis, and leachability tests by EPA Method 1313 showed that the optimal concrete products effectively immobilized the heavy metals in the combined ash.

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