rolled asphalt is used as the wearing course on most heavily trafficked roads in britain, and on the majority of these it performs very well. however, some conventional rolled asphalts have insufficient resistance to permanent deformation for roads which carry the heaviest traffic. in an effort to improve visco-elastic properties and resistance to permanent deformation, experiments have been carried out in which sulphur has been substituted for various proportions of the filler and bitumen components of the rolled asphalt mix. the properties of these modified mixes have been studied in the laboratory using the marshall test, the wheel-tracking test and measurements of dynamic modulus and fatigue life. these tests showed that resistance to permanent deformation should be improved by adding sulphur, with only a small reduction in laboratory fatigue-life. full-scale mixing and laying trials have also been carried out, and these showed that it is possible to manufacture and lay sulphur-modified asphalt providing its processing temperatures are carefully controlled. there are several problems that would need to be resolved, however, before this process could be used more widely. the nature and structure of sulphur in asphalt has also been investigated and this has improved the understanding of the role of sulphur in the mixing and its likely effects on more practical aspects, such as handling and road performance.(a)

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