Background The project addressed two major environmental problems that exist in every European country with significant industry and construction activities. Firstly, environmental damage is caused to the ecological system, landscape and ground water resources when non-renewable natural stone materials are used to construct roads, landfills and other civil engineering applications. Increasing restrictions on the use of natural resources creates problems of limited availability and increases the costs of raw materials for the construction sector. Secondly, there are vast quantities of industrial process waste uselessly deposited in landfills – either directly from the manufacturing process (like gypsum, sludge and filter-cake) or indirectly through incineration (ashes). This waste is an environmental problem both for the industry and society as a whole. In Finland alone, 4 million tonnes/year of process waste is being produced that could be used in geotechnical applications instead of depositing it. Industrial waste will never compensate for all natural stone materials, but it is estimated that it could potentially cover 20-25 % of the current consumption level. Objectives The objective of the “KUKKIA-CIRCLET” project was to demonstrate the sustainable, environmental and competitive benefits of road construction methods that reuse old road material and recycle high-volume waste from the paper (fibre sludge and fly ash) and chemical industry (process gypsum and filtercake) in the construction and maintenance of the secondary road network. The project was to test the new, innovative methods to the full scale, assess the performance of the new processes and show the favourable long-term environmental, technical, social and economic benefits of the new methods to various interest groups in Europe. It was intended that a wide exploitation of the project results was to protect non-renewable natural resources and reduce the quantity of waste and the need for landfills in Europe. Results The project planned and implemented four different types of road improvement interventions, each of them presenting different technical characteristics and problems. 1) A section of unpaved rural road of some 7 kilometres, suffering from deformations during frost-melting periods, was renovated by applying a thick surface layer, consisting of a mixture of gravel, paper sludge and fly ash. 2) Another, short unpaved rural road section of some 0,5 km suffering from structural weaknesses was renovated by adding a very thick surface layer also with a mixture of gravel, sludge and fly ash. 3) Approximately one kilometre of a paved regional road was widened to include light-traffic lanes (pedestrian and biking) in a road section with steep gradient again using a mix of gravel, fly ash and sludge material. 4) The last intervention was the construction of two sections of light-traffic lanes, one in a sensitive groundwater area and another which was to demonstrate the use of waste material mix in the surface layer instead of asphalt. The project surveyed the stability and technical characteristics of the constructions and also monitored the possible environmental impacts such as the leaching of harmful or hazardous substances from the waste material mix. The surveys and monitoring of the structural stability resulted in the conclusion that the waste containing material can easily replace the virgin gravel as a load bearing, structural element and that the material as surface element is as tough as the more commonly used fine gravel. In the light traffic lanes the waste mix gave a paved/asphalt like touch to the surface. No specific leaching was detected from the renovated structures. The waste containing material allowed steeper structural gradients, which obviously made certain renovation works easier. However, the practical working methods will need some fine-tuning and the commonly used road construction equipment some light modifications to be suitable for handling the material, which has slightly different physical characteristics compared to the traditional gravel mixes. For the time being, the waste-containing construction materials have no standards or classification. Each separate intervention is usually assessed, from the environmental point of view, as an individual exercise, which increases the costs. This project has contributed to the harmonisation of the practices and supports the case for standardization of the materials, which then could be applied in a more routine way in the design phase. The financial cost of the large volume waste is usually very low, which makes it an attractive substitute for virgin materials. However, long transport distances counterbalances the low cost of the waste material.