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Contact Stéphanie Staquet, Thibault Lenormand, Jérôme Carette
Keywords reactivity, lixiviation, municipal solid waste incineration
Prof. Ahmed Loukili, GeM, Central Nantes, France
Dr Emmanuel Rozière, GeM, Central Nantes, France
Dr Christian Pierre, CRIC-OCCN, Bruxelles 
Dr Aurore De Boom, CREA-SURF, ULB
Prof. Marc Degrez, CREA-SURF, ULB

Title of Project

Incorporation after treatment of Municipal Solid Waste Incineration fly ashes from electrostatic precipitator (ESP) in concrete
Description of the research project

Waste management has become one of the key priorities of European Union environmental policy. Waste prevention, material recycling and recovery are the main objectives of the European Union; energy recovery remains the best solution for waste which cannot be avoided nor recycled, while landfilling is discouraged. In that context, this project aims to valorise residues from thermal processes in construction materials; specifically, fly ashes and APC residues from Municipal Solid Waste Incineration (MSWI) are planned to be treated and added to cement or concrete, as hydraulic binders (mineral addition of type II) or inert filler, like sand and lightweight aggregates. Fly ashes and APC residues from MSWI are considered as hazardous waste mainly because of the leachability of chlorides and metals. As bottom ash can be reused in civil construction, these residues correspond to the ultimate residues from MSWI. They are usually placed in special landfill, after a treatment, and represent thus significant financial and environmental impacts.

Recent researches suggest using these residues in civil engineering applications, in particular as mineral additions to cement or concrete, after a pre-treatment stabilising or removing some problematic compounds. On the other hand, the construction industry suffers from a decrease of natural resources. The substitution of some natural constituents in the composition of construction material allows reducing the environmental impact due to the production of the cement in terms of CO2 gas emission into the atmosphere, by keeping a product of quality. In Belgium, coal fly ashes and blast furnace slag are commonly added to cement. However, the blast furnace slag supply becomes insufficient to cover the increasing demand in mineral additions.

The project proposes to solve both problems by developing a process using some fractions of fly ashes and APC residues in cementitious materials. It considers each MSWI fly ashes and APC residues separately and aims to treat the most appropriate residue to be incorporated in a construction material. Analyses and tests needed in this project will also provide new knowledge about the residues, the link between their chemical composition, their mineralogy and their reactivity and new understanding about eco-cement behaviour. Since the MSWI input daily varies, the residues variability will be also studied to guarantee a successful treatment and a final product of quality. According to the residues characteristics, a specific treatment is build up such as the treated residues can be incorporated in a construction material. The residues treatment is based on both physical (size-based) and chemical separation, according to recent research works of the project partners. Concerning the new eco-construction material, its properties can be adapted to complete some specifications. As this material is expected to be cheaper, it can be destined to some civil work which needs large quantities in volume. In term of delivery, the project plans to determine an exportable process of waste treatment and to obtain a technical approval which enables to commercialise the treated waste in cementitious materials.

MSWI fly ashes and APC residues could then be advantageously reused in Belgium, by taking benefit of their potential pozzolanic reactivity and their geographical proximity. For the cement industry, the MSWI fly ashes and APC residues valorisation furnishes a new mineral addition, easily available and marketable in cementitious materials. Furthermore, the valorisation of the MSWI fly ashes and APC residues in construction material contributes to the development of the industrial ecology, by transforming waste from an industry to primary material for another. Such a process reduces the global environmental impacts of both industries, the first producing less waste, the second consuming less natural resources and producing less CO2 gas emission into the atmosphere.