RELATIONSHIPS BETWEEN COMPOSITION, STRUCTURE, AND PROPERTIES OF ROAD ASPHALTS: STATE OF RESEARCH AT THE FRENCH PUBLIC WORKS CENTRAL LABORATORY

Abstract

Reviewed is the past and ongoing research conducted at France's Laboratoire Central des Ponts et Chaussees (LCPC) (Public Works Central Laboratory) in the area of asphalt cements. The investigations cover the development of methods for characterizing the physicochemical and rheological properties of such materials, and the establishment of relationships between their composition, colloidal structure, and practical properties. For physicochemical characterization, the research makes use of such techniques as high-pressure liquid chromatography, gel permeation chromatography (GPC), and differential scanning calorimetry. The rheological behavior of materials is studied by the peeling technique, viscoelastisimetry, and viscosimetry on thin films (with specially designed apparatus). Theoretical studies have led to the proposal of a new rheological behavior model better suited to experimental results than conventional models, characterized by its analogy with the laws of chemical kinetics, and allowing the calculation of a structural parameter as well as a parameter dependent on energy per unit volume dissipated and having activation energy characteristics. The foregoing assessment brings out the effectiveness of the facilities set up by the LCPC, and it is important to note that the new characterization methods indicate that asphalt cements with the same specifications have substantially different physicochemical compositions and rheological behaviors. Among the most important results, it is demonstrated that GPC makes it possible to characterize the equilibrium of the colloidal structure of asphalt cement and to obtain information on the ability of asphaltenes to interact to form a more or less developed network responsible for the gel character of the rheological behavior noted. It is also demonstrated that information obtained by GPC on the interaction of asphaltene micelles is closely correlated with certain observed characteristics of rheological behavior.