The design and performance of thin surfacing layers

Although thin surfacing layers are not new, there has been a dramatic increase in their use on major roads over the last twenty years. These newer thin surfacings were originally developed in the 1980s and, in some parts of Western Europe, are now the preferred surfacing layer. This paper reviews the design considerations of a range of thin surfacing systems within Europe and elsewhere and outlines the advantages over more traditional surface treatments. The scope for innovation is high and both wide grading ranges and different layer thicknesses have been successfully used. The binder used, the mixture chosen and the construction practice are all important components to achieve a performing and durable material. The performance of a number of road contracts carried out under a range of climatic conditions is reported, including performance data from Poland, Sweden, United Kingdom and the United States of America. The road sites are still under assessment and all are performing satisfactorily. Given the wide application range for thin layer technologies. the paper also discusses the possible failure criteria for the various thin surfacing systems and attempts to give an indication as to likely surfacing life.