A Retrospective Study Quantifying the Effects of Mixture Design and Constituent Properties on Asphalt Pavement Roughness

Given the importance of pavement surface, many transportation agencies have developed technical specifications to serve as a baseline for ensuring the quality of initial pavement roughness after paving works, monitoring it over time as an indicator of serviceability, and then referring to it as a threshold for strategic scheduling of pavement repair and maintenance works. Past studies have shown that various external factors are involved in determining pavement roughness; however, how principal asphaltic design parameters may affect initial pavement roughness has not been examined so far. To close this gap, this study investigated the contribution of the basic concepts of the Marshall mixture design method and individual constituent properties by analyzing the international roughness index (IRI) values of the asphalt wearing course of nine different roads with a total length of 435 km. The evidence from this study suggested that the strongest relationship at the mixture level was observed between Marshall stability and IRI, whereas optimum bitumen content had no influence on IRI. At the ingredient level, among various material properties, the specific gravity of fine aggregate was found to have the most pronounced effect on IRI. Consequently, particular attention should be devoted to these two factors to further improve IRI values at the mixture design stage.

Once put into service, asphaltic pavements experience detrimental deteriorations because of repeated load-based stress and environmental conditions that result in an increase in pavement roughness. Defined as “irregularities of pavement surface,” roughness is used for rating road serviceability, assessing paving quality, monitoring network condition, and optimizing investments in preservation, rehabilitation, and reconstruction of pavements. Furthermore, roughness is known to affect pillars of riding safety and driving costs. Correspondingly, most transportation agencies around the world developed technical guidelines to determine the initial roughness of the pavements newly opened to service. To improve these guidelines, more factors affecting initial pavement roughness should be uncovered. Bearing this in mind, the study presented in this paper strives to examine the comprehensive factors of asphalt design parameters and material properties to elaborate on what affects initial pavement roughness at the design level. The study results demonstrated that the strength of the paving mixture and the density of fine particles used in the mixture are of great importance for initial pavement roughness. Hence, in order to construct sustainable and cost-effective road pavements with desirable roughness, the impact of these two factors should be considered when designing asphalt mixtures.