In a world context, recycling of road-making materials has long been recognised to have the potential to conserve natural resources and reduce the energy used in production. The useful life of a bituminous pavement depends on a number of factors, such as the traffic loading, the environment, the drainage and the quality of construction. Timely maintenance can extend the life of a bituminous pavement, but if it is delayed then the bituminous
surfacing will often crack and will then need to be removed prior to rehabilitation. This is often the case in tropical countries where the rapid oxidation of the bitumen at the surface of the mix causes premature cracking which starts at the top of the bituminous surfacing and propagates downwards. Thick bituminous surfacings in tropical climates are also prone to
failure through deformation in their early life. These types of failures occur particularly in areas of slow moving traffic such as junctions and climbing lanes. With the increasing use of thick bituminous surfacings in the emerging countries the disposal of these surfacings is a waste of valuable natural resources and more effort needs to be made to re-use these materials as part of the reconstruction process.
UK and European attitudes towards the environment have also changed rapidly and the conservation of natural resources has become an extremely important issue. Today, in some European countries, recycling is a standard alternative for both construction and maintenance particularly in countries where there is a shortage of road-building aggregate or where there are
no indigenous oil reserves.
This unpublished Report reviews cold mix and hot mix recycling practices world-wide, and shows that there is no commonly accepted design method for cold mix recycled materials. For partial depth recycling the Marshall method, the Hveem method, resilient modulus and indirect tensile tests are all used by different authorities in the USA. The same is true for full depth recycled materials with CBR and unconfined compressive strength tests being used for modified materials in South Africa whereas for similar materials in Australia the resilient modulus and deformation characteristics are used in the design. There is no such divergence in the adopted design procedure for hot mix recycled materials where, besides specialised surfacing recycling techniques, the majority or road authorities outside Europe use a form of the design method proposed by the Asphalt Institute.
The review also considers the alternative methods of reclaiming, crushing and storing asphalt material and how it is processed through both batch and drum hot mix asphalt plants. Examples of sampling, testing and designing hot mixed recycled materials and the early results from cold-mix recycling trials are given in the Appendices of the report.
Smith, H.R.; Edwards, A.C. Recycling of bituminous materials: final report. (2001)