Effects of Combined MSWI Flue Gas Treatment Residues, Fly Ash and Boiler Dust on the Properties of Cement Mortars

This study evaluated the feasibility of using two hazardous residue streams from municipal solid waste incineration (MSWI) as partial substitutes for conventional constituents of cement mortars. A mixture of solid residues from flue gas treatment and fly ash (MSWI-SW/FA; 19 01 07* and 19 01 13*) was used as a partial replacement for natural sand, whereas boiler dust containing hazardous substances (MSWI-BD; 19 01 15*) was used as a partial cement replacement. The residues were incorporated separately and simultaneously at different replacement levels. Mortar consistency, compressive and flexural strength after 7 and 28 days, water absorption, freeze–thaw resistance, and microstructure were evaluated. At low replacement levels, mechanical properties remained close to those of the reference mortar. After 28 days, the best mixture containing both residues reached compressive and flexural strengths of 50.68 and 9.01 MPa, compared with 52.23 and 9.36 MPa for the reference mortar. Increasing MSWI-BD content reduced strength and increased water absorption, whereas MSWI-SW/FA improved freeze–thaw resistance. The most favorable freeze–thaw performance was obtained for MIX 2.93/17.07, with only a 3.20% reduction in compressive strength after 25 cycles. Mortar performance depended strongly on residue type, replacement level, and relative proportion.