The landfilling of municipal incineration residues is an expensive option for municipalities. This work evaluates an alternative way to render waste inert in cement-based materials by combining the reduction of waste content with the immobilization properties of metakaolin (MK). The functional and environmental properties of ternary and quaternary binders using cement, metakaolin, and two industrial by-products from combustion processes (MSWIFA - Municipal Solid Waste Incineration Fly Ash and SSA - Sewage Sludge Ash) were evaluated. The binders were composed of 75% cement, 22.5% metakaolin and 2.5% residue. Results on the impact of residues on the functional and environmental behavior of mortars showed that the mechanical, dimensional and leaching properties were not affected by the residues. In particular, the use of metakaolin led to a significant decrease in soluble fractions and heavy metals released from the binder matrix. The results are discussed in terms of classification of the leaching behavior, efficiency and role of metakaolin in the immobilization of heavy metals in of MSWIFA and SSA, and the pertinence of the dilution process. (C) 2012 Elsevier B.V. All rights reserved.