THE DEVELOPMENT OF THE BENDING BEAM RHEOMETER; BASICS AND CRITICAL EVALUATION OF THE RHEOMETER

The bending beam rheometer is proposed by the Strategic Highway Research Program (SHRP) for direct measurements of the rheological properties of asphalts at the lowest pavement temperatures. The purpose of this paper is to present the basic concepts upon which the rheometer was developed, to describe the testing procedure and the important procedural factors that affect test results, and to discuss the methodology of data interpretation. Typical results from the research program using a large number of asphalts to evaluate the rheometer are presented to illustrate the differences in behavior of asphalts from different sources and of different grades. The paper highlights the features of the testing system and the specimen preparation procedure. The results of the rheometer evaluation indicate that the rheometer is a repeatable test that can be used effectively to characterize the visco-elastic nature of asphalts at the lowest pavement temperatures. The paper includes discussion of the rationale behind selecting the specification parameters and the specification criteria to enhance binder contribution to resistance to thermal cracking.