Reexamining C-phi concept for asphalt paving mix design

The study of applying the C-phi (cohesion and angle of friction) concept to asphalt paving mix design was once an active area of research in the early 1950s. Further research, however, was not pursued subsequently probably du e to the complexity and long duration of the laboratory triaxial tests, and the difficulties encountered in relating the test results to field behavio r of paving mixtures. Today, with much more advanced test equipment and pow erful analytical and computation tools, another look at this theoretically sound approach is justified. By means of a C-phi finite element model, this paper illustrates that a link between Marshall test results and the triaxi al test properties of C-phi can be established analytically. This presents a useful tool for analyzing past pavements that were designed on the basis of Marshall criteria. The analytical model is also used to reestablish the C-phi based asphalt paving mix design concept proposed by Smith in 1950, an d to show that Smith's analysis model is a poor representation of multilaye r asphalt pavement systems. Of special interest is that the proposed analyt ical C-phi model is able to analyze the behavior of asphalt pavement under load, thereby permitting the incorporation of mechanistic or semimechanisti c distress models into asphalt mix design as well as pavement thickness des ign. It thus offers a potentially useful basis for an integrated procedure for asphalt paving mix design and asphalt pavement design.