Asphalt cement has been used over a century for roadway contstruction in United States. Historically,one of the most extensively studied physical properties has been the viscosity of the asphalt binder, in particular, how the viscosity of the asphalt binder changes during a pavement's lifetime. Many attempts have bene made to relate the viscosity of the binder to its chemical composition and molecular structue. One complicating factor to understanding the exact relationship between viscosity and chemical composition arises from the extremely complex chemical composition (an asphalt may contain thousands of individual components). Another complicating factor arises from the ever changing chemical composition of the binder throughout the pavement's lifetime as a result of low temperature oxidation. As a result, most attempts to correlate a binder's viscosity to the binder's chemical composition have been in terms of only a few pseudo-components. The components found to have the greatest influence on the viscosity are referred to collectively as the asphaltenes.
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