Incorporation of Municipal Solid Waste Incinerator Fly Ash into Concrete: A Sustainable Approach

Abstract

Municipal Solid Waste (MSW) Management is a great challenge facing countries worldwide. While landfilling has been considered the cheapest and most efficient approach for dealing with MSW, it proved to have many environmental, social, and economic drawbacks. Therefore, many countries adopted alternative technologies to safely manage their MSW. Incineration, being one of these adopted technologies, demonstrated to be very effective in drastically reducing the quantities of waste (by weight and volume), in addition to the possible energy recovery in the form of heat and electricity. In this context, for a small country like Lebanon, generating more than 2.7 million tons of waste annually, controlled MSW incineration is necessary. Incineration involves the combustion of waste materials resulting in the formation of flue gases, ash, and heat as by-products. The major environmental concern of incineration is flue gases, as they are hazardous and should be controlled using proper filters. Another environmental concern is managing the ash residues, namely fly ash, as it contains most of the inorganic toxins and heavy metals and is often dumped in landfills, posing a great threat to groundwater. This research aims at solving this particular problem through the incorporation of MSW incinerator fly ash in concrete with partial replacement of cement. Fly ash acquired from SICOMO, a Lebanese MSWI located in Lebanon, was characterized by analyzing its physical and chemical properties to ensure its compatibility as a replacement material to cement in cement mortars. Results indicated that fly ash from SICOMO showed characteristics similar to other MSWI fly ashes reported in the literature, enabling us to use it as a partial replacement to cement without any pretreatment. To investigate the compatibility of this partial incorporation, cement mortars containing 10% (by weight) replacement of cement with fly ash were prepared and tested for compressive strength. Results showed that cement mortars containing 10% cement replacement achieved 97% of the 28-day compressive strength of control cement mortars. To find the optimum percentage replacement and promote more use of fly ash, additional batches containing 15% and 20% (by weight) replacement of cement were prepared and tested for compressive strength, achieving 81% and 74% of the 28-day compressive strength of control cement mortars, respectively. Such replacement offers a sustainable feature to the concrete since the carbon footprint associated with the inclusion of cement is reduced. Lastly, leachability tests of different heavy metals (Pb, Cr, and Cd) were carried on whole, demolished, and loose cement mortars incorporating fly ash, to check the environmental impact associated with this incorporation. All results indicated proper entrapment of metals in the hardened cement mixture, with concentrations of metals in the water not exceeding the allowable limit in waste set by the Environmental Protection Agency (EPA). This research provides a green sustainable solution for managing MSW through incineration, by reducing the resulting amount of fly ash, and lowering the carbon footprint of concrete.