TEMPERATURE CONSIDERATIONS IN ASPHALT-AGGREGATE MIXTURE ANALYSIS AND DESIGN

Abstract

The objective was to develop and demonstrate techniques for incorporating the effects of in situ temperature in the mixture-design process without adding significantly to the complexity of testing and analysis. The recommended approach converts the expected traffic, expressed in terms of equivalent single axle loads (ESALs) according to conventional AASHTO practice, into its equivalent value at critical pavement temperature. For both fatigue and permanent deformation, acceptable mixtures are those that resist equivalent laboratory loading in cyclic tests conducted at the critical temperature. Critical temperatures, the points at which most damage occurs in situ, were developed for nine climatic regions throughout the United States using the FHWA's Integrated Climatic Model for determining in situ temperatures. For 20-cm (8-in.) pavements, more than 40% of the fatigue damage and more than 64% of the permanent-deformation damage occurred within a 5 deg C (9 deg F) range centered on the critical temperature. Temperature equivalency factors, used to convert ESALs at one temperature to their equivalent at the critical temperature, were found to depend on mode of distress, the pavement structure, and the asphalt mixture--but to be independent of climate. When multiple temperature laboratory testing is required, for example, when reliability must be unusually high, suitable temperature ranges are 15 deg C to 30 deg C (59 deg F to 86 deg F) for fatigue testing and 30 deg C to 45 deg C (86 deg F to 113 deg F) for permanent-deformation testing.