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Use of secondary materials in landfill constructions
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
Ecoloop, Stockholm.
Telge AB.
2007 (English)In: SARDINIA 2007: Eleventh International Waste Management and Landfill Symposium ; [1 - 5 October 2007, S. Margherita di Pula, Cagliari, Sardinia, Italy] / [ed] Raffaello Cossu, Cagliari: CISA, Environmental Sanitary Engineering Centre , 2007Conference paper, Published paper (Refereed)
Abstract [en]

Many landfills are subject to closure in the near future. Roughly 2,000 hectares of land­fill area have to be covered only in Sweden, equivalent to about 100 million tonnes of construction material. In addition to material costs in the order of tens of billions Euro, this also puts a strain on the environment through the exploitation of non-renewable virgin construction materials. Many landfill operators are considering alternative cover designs and materials in order to reduce resource spending. However, there is a fair amount of uncertainty with regard to functional and environmental consequences of using alternative (secondary) materials, both from the side of the companies and the authorities. This paper gives an overview over potential waste based construction materials and the use of some of them in projects presently ongoing in Sweden.Research on the use of secondary materials in landfill covers is quite recent. Substitutes for natural or synthetic materials in a landfill cover can be various types of waste from process industry, construction and demolition, or comparable activities. Alter­na­tive mate­rials that have been investigated are ashes, slags, sewage and fibre sludges, treated soils and com­post. Table 1 gives an overview over potential waste based construction materials. The total of potential materials is well in excess of the material needs for landfill construction, but they may not be available at the right time, place or quality.Besides being economically viable, the substitute materials should have suitable technical and environmental properties in order to secure a proper function of the construction. Experiences from three field studies (landfills at Tveta/Södertälje, Hagfors and Alvkarleby) are discussed looking at relevant issues during 1) construction, 2) active after care phase, and 3) long term processes.Using SCM poses additional problems compared to using conventional materials. Often, the supply of material has to be planned in advance and the materials may have to be stored on site. Storing, however, can cause problems if the materials have properties that change over time e.g. due to climate. For other materials storing may be necessary in order to achieve desired properties. One example is the ageing of strongly alkaline materials that react with atmospheric carbon dioxide and thus obtain better leaching properties. Table 1 Overview over potential waste based construction materials and examplesSourceExamplesMining and mineral industryWaste rock, flotation sand, etc...Construction and demolition (C&D)Crushed concrete, gypsum, asphalt, reinforced polymers, woodProcess industryDifferent types of slag from steel making, green liquor and fibre sludge from paper production, ashes and foundry wastesWastewater treatmentDigested sewage sludge, sandIncinerationBottom ash, fly ashThe evidence is mounting that the desired technical function of a landfill cover can be attained using suitable combinations of secondary construction materials. So far, all three field tests indicate leachate amounts between less then one and 30 l (m2 yr)-1 below the liner. In comparison with the average annual precipitation of about 600 mm yr-1 at the Swedish East coast, only 0.2-5 % of the precipitation seeped through the liner so far; i.e. the leachate generation is reduced with about 90 % or more.The issue is more if the materials may cause adverse impacts of the landfill and its recipients. A low water infiltration through the liner means that the most of infiltrating water is removed as drainage water and thus the leaching of the layers above the liner are of the greatest concern.Infiltrating water will yield a liquid to solid ratio of about 1-2 l kg-1 in the layers above the liner after about 10 years. The most mobile elements, such as nitrogen, will be leached to a great extent already at such low L/S ratios, so a forecast with regard to the need of treatment of drainage water points at about two to three decades.In the long term perspective the mineral changes of the construction materials become important. E.g. one of the incentives for using fly ash in liners is their capacity for chemical-mineralogical changes leading to the formation of clay-like structures. This could mean that a liner built of ashes will attain a lower permeability over time. Other mineral changes that can occur in ashes include the trapping of metals in the structure, e g in clay and carbonate phases.Much is still to be learned about the long term processes and the factors that control them. Ongoing studies include the assessment of climatic variables, different material combinations as well as the impact of landfill gases.The following conclusions can be drawn:The use of secondary materials in construction is important due to substantial resource and environmental impacts. An increased use should be beneficial, provided that the problems of using such materials can be managed.In addition to legislative and bureaucratic barriers, there are also practical issues which need to be dealt with in order to pave the way for a wider use of alternative construction materials. In the construction phase more planning is needed due to temporal and geographical limitation of the material availability. Some materials are not ready for immediate use but need to be pre-treated. All of these factors may cause a need for more space and time. A system for quality assurance comparable to that of traditional construction materials is another issue that needs to be resolved. Most likely some kind of legislative pressure is needed for this.In the medium term leaching of pollutants from the construction materials may be the most important issue when using secondary construction materials, which underlines the double standards applied, since traditional construction materials will not be scrutinized in the same manner. Anyhow, the long term interactions between materials and their environment need to be considered and further studies are necessary for secondary construction materials as well as for conventional materials. Existing data indicate both possibilities and problems.In the long term issues of material interactions will remain and the mechanical impact of mineral changes in the secondary construction materials may be added to the list of issues to clarify. Some of the material changes may be beneficial for the function of the construction, e.g. clay formation in liner materials may make them more impervious, but there may also be negative changes caused by deteriorated material properties. The rate and extent of such processes and the factors that enhance or retard them need to be understood better.Secondary construction materials have always been used and some of the "traditional" materials used today were wastes before. There is no reason to believe that this development should not continue.

Place, publisher, year, edition, pages
Cagliari: CISA, Environmental Sanitary Engineering Centre , 2007.
National Category
Other Environmental Engineering
Research subject
Waste Science and Technology
Identifiers
URN: urn:nbn:se:ltu:diva-31839Local ID: 6234b900-685a-11dc-a0c3-000ea68e967bISBN: 978-88-626-5003-8 (print)OAI: oai:DiVA.org:ltu-31839DiVA, id: diva2:1005073
Conference
International Waste Management and Landfill Symposium : 01/10/2007 - 05/10/2007
Note
Godkänd; 2007; 20070921 (laan)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved

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