CONCEPTS USED FOR DEVELOPMENT OF BITUMEN SPECIFICATIONS

The evolution of bitumen specifications has been dramatic in the last 15 years. Simple empirical tests based on mechanical properties formed the first types of binder tests. More recently however, fundamental, visco-elastic and damage characterization methods have been adopted. Changes in specifications have been motivated by various factors and have had various consequences in different parts of the world. In this paper, the authors bring together their experience of working in three different continents, to evaluate various bitumen specifications and discuss merits of different concepts used from as early as 1950 to 2003. The paper shows how the Bitumen Test Data Chart (BTDC), and the van der Poel nomograph, which is based on penetration and softening point, could be used to link the empirical test results to performance related properties such as stiffness and strength and how these derived measures could be linked to traffic volume, traffic speed and pavement design temperatures similar to the Superpave PG system. The approach is used to discuss the current South Africa Specification and to propose a possible performance grading system for South Africa using actual climatic and traffic data. Finally, this paper covers the most recent changes proposed in the USA and Europe for the original Performance Grading concept, aimed at including Polymer Modified Bitumen.