A Review of Research Pertaining to Asphalt Composition and Its Relation to Quality

About the report:

This report reviews both early and recent research on asphalt quality with emphasis on compositional factors and how the findings of such research relate to present-day problems with asphalt cements and asphaltic paving mixtures. It is shown that historically the quality of an asphalt as a paving material has been judged by its physical characteristics and its performance in a pavement. However, when properly used, asphalts of widely different physical characteristics can provide good service. Conversely, if asphalts that normally provide good performance are used in improperly designed mixtures, poor performance can result. Accordingly, since many factors enter into pavement performance and these factors often interact with each other, it is difficult to define the quality of an asphalt on the basis of its characteristics alone. Because of the complexity of the chemical composition of asphalt, it is necessary that analyses of asphalts be based on determining types of compounds or groups of constituents having similar behaviors. Several procedures are available for such analyses, but there is no universal agreement among chemists and asphalt technologists as to which procedure is best. Research has also shown that asphalt-aggregate interactions vary depending upon the characteristics of the aggregates as well as those of the asphalt. Thus, an asphalt exhibiting optimum behavior with one type of aggregate may exhibit significantly different behavior with another aggregate. Accordingly, although it is recognized that physical characteristics are established by chemical composition, materials with significantly different compositions can possess similar physical characteristics. It is concluded that asphalt specifications based on chemical composition do not now, or in the near future, appear feasible. However, expanded research to better define the relationship of physical characteristics to chemical composition is needed and should provide knowledge that upgrading poor or borderline asphalt cements through adjustment of composition or the use of additives.

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