Reexamining C–ϕ Concept for Asphalt Paving Mix Design

The study of applying the C–ϕ (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 due to the complexity and long duration of the laboratory triaxial tests, and the difficulties encountered in relating the test results to field behavior of paving mixtures. Today, with much more advanced test equipment and powerful analytical and computation tools, another look at this theoretically sound approach is justified. By means of a C–ϕ finite element model, this paper illustrates that a link between Marshall test results and the triaxial test properties of C–ϕ 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–ϕ based asphalt paving mix design concept proposed by Smith in 1950, and to show that Smith's analysis model is a poor representation of multilayer asphalt pavement systems. Of special interest is that the proposed analytical C–ϕ model is able to analyze the behavior of asphalt pavement under load, thereby permitting the incorporation of mechanistic or semimechanistic distress models into asphalt mix design as well as pavement thickness design. It thus offers a potentially useful basis for an integrated procedure for asphalt paving mix design and asphalt pavement design.