Use of tyre shreds in civil engineering applications technical and environmental properties

Sammanfattning: End-of-life tyres are a disposal problem regarding the large volumes produced every year. Tyre shreds are primarily produced to reduce the transportation volumes of end-of-life tyres after collection. Within the European Union, there is a ban for landfilling tyre material in order to reduce the total landfilling volumes and to encourage recycling measures. Until recently the main disposal option has been energy recovery in industrial processes. However, legislation acts has recently been taken in the European Union to encourage recycling and recovery of end-of-life-tyres and re-use of tyre materials in construction works is listed as one disposal option. Tyre shreds possess interesting technical properties that could be beneficially used in civil engineering applications. Some characteristic properties of tyre shred materials are the low density, high elasticity, low stiffness, high drainage capacity and high thermal insulation capacity. These properties open up possibilities for utilisation of the material in an innovative manner. The overall aim of this thesis work has been to describe and evaluate tyre shreds as a civil engineering construction material from environmental and technical point of view. The thesis work has included laboratory tests and full scale field tests to investigate technical and environmental properties of tyre shreds and to investigate the tyre shred material behaviour in a real road construction. Furthermore, the state-of-the-art knowledge in the area has also been analysed and presented. In the laboratory studies technical properties focused on compaction and compression behaviour of tyre shreds have been investigated. In a field study of a built road, tyre shreds has been tested and evaluated, during four years, as lightweight fill and frost insulation material. Environmental properties of tyre shreds, mainly leaching characteristics, have been studied in laboratory tests and monitored in two full scale field tests. Based on the results in the laboratory studies a model is proposed for evaluation of stressstrain properties and prediction of compression behaviour. Recommendations for construction works and pavement design are suggested based on the road construction field study results. Conclusions regarding the studied leaching properties of tyre shreds, based on the laboratory tests and the field monitoring, are that zinc and iron are the metals mainly released and that the release of the studied organic compounds, i.e. PAH and phenols, are low. From an environmental point-of-view focus should be moved from PAH-compounds towards other compounds that are more interesting from mobility perspective and lack of knowledge. It is concluded from this thesis work that PAH is not a pollution problem in the area of use of tyre material covered by this work. Applications where tyre shreds have been successfully utilised as construction material, are e.g. as draining layers in landfills and as material in trotting tracks and paddocks. The utilisation of the material in trotting tracks and paddocks is especially interesting since the unique elasticity of the material is utilised. The potential of utilising tyre shreds in civil engineering construction is big. Since the available amounts of material is limited there is a possibility to direct the use of tyre shreds to the most favourable applications of tyre shreds and still solve the disposal problem of end-of-life tyres.