SPECIFICATIONS, PROPERTIES AND PERFORMANCE OFASPHALTIC MATERIALS IN THE UNITED STATES Rsum Asphalt is a major material for highway construction and maintenance in the United States. Current specification tests to measure flow properties are empirical and requirements have been developed on a trial and error basis. Research and development studies are under way in the United States to develop fundamental tests and knowledge to define the essential engineering properties that can be used in specifications. A "Research Specification" based on fundamental viscosity tests has been proposed in the United States and the form is similar to that presented at the 6th World Petroleum Congress. The proposed specifications appear to offer a sound basis for continuing research directed toward characterizing asphalt in terms of engineering properties.
The requirements of the two specifications are compared and data on asphalt cements produced in the United States are summarized. The properties measured by fundamental tests vary appreciably in the low temperature range. Continued research is recommended to develop knowledge relating fundamental properties of asphalt to the fundamental properties of asphalt-aggregate systems and to pavement performance. Tests selected for a rational specification for asphalt should be reliable, simple and rapid. Requirements should recognize variability due to manufacturing, sampling and testing but should control the properties that are critical to optimum pavement performance.
Asphalt is a major material used in the construction and maintenance of highways in the United States. Highway Statistic's shows a total of 3,644,069 miles of highways and streets of which 2,730,336 miles are improved with some type of surface. Almost 50 per cent of the improved road mileage has some type of bituminous surface. Of the remainder, four per cent is concrete and the balance is improved with selected by J. Y. WELBORNBureau of Public Roads, Department of Commerce, U.S.A.
Cet article prsente une revue des mthodes utilises actuellement aux Etats-Unis pour le choix des matriaux asphaltiques routiers destins tre employs dans diffrentes conditions de trafic et de milieu ambiant, et montre la varit des proprits attendues des bitumes selon les normes habituelles. Des normes nouvelles sont ncessaires pour:
Dfinir les proprits des bitumes de manire choisir celles qui conviennent le mieux aux conditions particulires de trafic et de milieu ambiant.
Dfinir les proprits techles. Des normes nouvelles sont ncessaires pour calculer les mlanges routiers, construire les routes et leur donner une bonne tenue en service.
Etablir les meilleures limites pour des normes qui, tout en tenant compte de variations acceptables, fixent, en mme temps, les valeurs des caractristiques assurant les meilleures conditions de service et de rendement. soil or aggregate materials. Excluding the latter, the bituminous types comprise over 90