Overlay Thickness Design for Low-Volume Roads
Identifying the appropriate overlay thicknesses is critical to a local transportation agency's ability to maintain its pavement network. Local agencies often use empirical approaches for designing the overlay thickness for low-volume pavements. For example, overlay design for low-volume roads in Illinois is currently carried out using assumed layer coefficients for a limited number of material types. Although such empirical approaches are fairly simple to use, they are often not suitable for considering the effects of recycled and nontraditional construction materials that are more commonly considered in current-day sustainable pavement applications. The lack of mechanical testing for evaluating the pavement structural condition often leads to uneconomical practices in the rehabilitation of low-volume roads. This paper presents a mechanistic–empirical approach for overlay thickness designs of low-volume pavements through a combination of nondestructive deflection testing and preestablished pavement damage models. Five pavement sections, with varying structural and traffic characteristics, were selected from two counties in Illinois. Three sets of falling weight deflectometer tests were conducted over a period of one year to monitor changes in pavement deflection responses. Structural conditions of the pavement sections in their original configuration were evaluated first. Then, the corresponding required overlay thicknesses were determined by using two methods currently used by local agencies. The inability of the currently available methods to properly account for current pavement structural conditions was highlighted. A new mechanistic–empirical overlay thickness design method introduced in this study successfully identified structural deficiencies in the original pavement configurations.