| Summary: | The lifespan of asphalt surfacing materials can vary from a very short duration, when temporary surfacing is considered, to up to 25 years for permanent surfacings. Throughout their lifespan the surfacings are expected to contribute to the provision of adequate levels of friction. The purpose of this research is to examine the variation of friction characteristics of road surfacing materials with time. The asphalt industry has undergone considerable change over the past two decades. This has seen the dominance of hot rolled asphalt and bituminous macadams (now asphalt concrete) being replaced by a spectrum of asphalt mixes specifically designed to offer a wider range of enhanced characteristics. Skidding resistance has remained as a priority requirement. Research has highlighted that there are distinct periods during the life of asphalt road surface materials. The existing standards are based on an equilibrium period during which there is seasonal variation with an overall downward trend to a value at which the surface warrants investigation prior to possible resurfacing or some other type of treatment. For some materials, there is an initial period of lower than expected skidding resistance found to last from a number of days, weeks to months and is termed early life. The majority of laboratory studies undertaken in this thesis were designed to reflect either real or hypothetical scenarios that could be encountered on an in-service highway surface. The programme of work considered the development of skid resistance for a range of surfacing materials from initial compaction until they have reached their equilibrium and are failing for different reasons. There were distinct generic relationships and the development of friction properties has different timelines depending on factors such as aggregate type, asphalt type, bitumen type and stressing conditions. The findings of the research will necessitate the revision of current Irish standards that will bring it closer in line with other European countries. This will probably involve the use of smaller stone size mixes and lowering the requirements for texture depth. It is anticipated that the improved understanding of the implications of poor practise will lead to better quality road surfaces in Ireland.
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