Life cycle assessment model for road construction and use of residues from waste incineration

Harpa Birgisdottir

Research output: Book/ReportPh.D. thesisResearch

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Abstract

Large amounts of materials are used in the road sector. The use of virgin materials predominates, but recycled materials are used increasingly. Construction of new roads often implies considerable interference with the environment, both related to the alignment of the road and the procurement of the large amounts of natural aggregates needed for the construction. Residues from waste incineration, especially bottom ash, can be utilized in road construction. In Denmark, approximately 80% of the 640 000 tons of bottom ash generated annually are utilized for construction purposes. The use of residues promotes the goals of minimizing the use of natural resources. However, many residues have a chemical composition that differs considerably from that of conventional materials, and when in contact with water constituents might leach from the materials into the environmental compartments. Introduction of residues into the road area therefore calls for augmented awareness of the environmental impacts. Laboratory leaching tests and field tests have been used to both estimate leaching from residues and for comparison with conventional materials. Assessment methods, such as risk assessment and life cycle assessment, assessing the overall environmental impacts related to the residues have been suggested as a means of evaluating the consequences of recycling in broader perspective.

A new life cycle assessment model for road construction and disposal of residues, named ROAD-RES, has been developed. The model has two purposes: (i) to evaluate the environmental impacts and resource consumption in different life cycle stages of road construction with virgin materials and residues from waste incineration; (ii) to evaluate and compare two disposal methods for waste incineration residues, namely landfilling, and utilization in roads. Methods to predict the leaching from materials as well as the distribution of leached constituents into the five environmental compartments (air, soil, groundwater, fresh surface water and marine surface water) have been developed and preliminary values are provided. The model includes a new characterization method for contamination of groundwater due to leaching of salts; this method is named Potentially spoiled groundwater resource. In addition, characterization factors for Human Toxicity through groundwater due to emissions of heavy metals have been calculated. To account for the long-term leaching, the model includes a new impact category: Stored Ecotoxicity in water and soil that accounts for the presence of heavy metals and very persistent organic compounds that in the long term might leach.

The ROAD-RES model has been used in the assessment of two hypothetical case studies: disposal of municipal solid waste incineration (MSWI) bottom ash, and construction of secondary road with and without MSWI bottom ash. The outcomes of the cases studies have shown that the model is useful for making comparisons of different options, for both road constructions and disposal of residues. The model has been thoroughly tested for errors, both in the calculation method of the model and the data available in databases.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherDTU Environment
Number of pages45
ISBN (Print)87-89220-92-7
Publication statusPublished - Sep 2005

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