The need for overlay design solutions for deteriorated roadways in Illinois is great. With increasing construction of ultra-thin whitetopping (UTW) pavements in Illinois, it was important to assess the performance of those pavements. To address this need, IDOT funded a study conducted by the Illinois Center for Transportation (ICT).
The two main components of the study were (1) visual distress surveys of 20 existing UTW pavements in the state ranging in age from 1 to 15 years and (2) falling weight deflectometer (FWD) testing of eight of those projects. (Ultra-thin whitetopping, as defined in this project, is a 3.5- to 6-inch Portland cement concrete overlay bonded to an existing asphalt concrete or composite pavement.)
Jeffery Roesler, professor in the Department of Civil and Environmental Engineering (CEE) at the University of Illinois at Urbana-Champaign, served as principal investigator for the study. Daniel King, a graduate student in CEE at Illinois, served as research assistant.
The primary purpose of the visual distress surveys was to evaluate the UTW projects by documenting all observed distresses and to determine the design features that provide favorable—as well as unfavorable—performance. The surveys provided IDOT with significant insight as to whether the existing design methodology used in Illinois is sufficient in areas such as slab thickness, panel size, use of macro-fibers, and construction choices.
Because UTW layer thicknesses and support conditions can vary along a project, it can be difficult to characterize the load-carrying capacity of a UTW pavement at a given point. Therefore, the ICT researchers also conducted falling weight deflectometer (FWD) testing. In FWD testing, dynamic loads are applied to a pavement surface to simulate the load produced by a rolling vehicle wheel. In the ICT study, deflection data collected during FWD testing were used to directly calculate the load-transfer efficiency and assess joint performance, but there was no existing method to assess in situ structural properties of UTW pavement. The research team addressed this challenge by deriving and applying a backcalculation procedure to the deflection data derived from the FWD testing.
“Our field surveys and the new FWD backcalculation procedure demonstrated that IDOT’s design procedure was providing adequate performance. Additionally, we found that macro-fibers in the concrete have helped in resisting crack propagation, kept existing cracks tight, and minimized misalignment between adjacent slab panels,” says Roesler.
IDOT’s Charles Wienrank, who led the Technical Review Panel that oversaw the research project, says, “Professor Roesler and his research assistants evaluated the performance of several whitetopping projects throughout the state. They were able to validate the thickness design procedure currently being used by IDOT and make recommendations on design details. Professor Roesler continues to provide IDOT with valuable guidance on the design and construction of rigid pavements.” Wienrank is a Pavement Design Engineer in IDOT’s Bureau of Materials and Physical Research.
The study, titled “Mechanistic-Empirical Design, Implementation and Monitoring for Rigid Pavements” (R27-061), was conducted in fiscal years 2012–2014. A copy of the project’s final report is available on ICT’s website.