Local and state highway agencies dedicate a significant portion of their annual pavement management and rehabilitation budgets for assessing the condition of in-service pavements. To aid agencies in selecting an adequate, effective, and economical rehabilitation strategy, an accurate means for evaluating the functional and structural deficiencies of an existing pavement is necessary. For that reason, a project was initiated by the Illinois Department of Transportation (IDOT) to demonstrate the advantages of nondestructive testing (NDT) and evaluation for local agency pavement rehabilitation.
In the research study (“Development of Improved Overlay Thickness Design Alternatives for Local Roads”) conducted by the Illinois Center for Transportation (ICT), pavement sections with varying structural and traffic characteristics were selected in six Illinois counties. The objectives of the study were to develop hot-mix asphalt (HMA) overlay thickness designs based on various models; evaluate the advantages, disadvantages, and costs of each design alternative; and demonstrate through nondestructive falling weight deflectometer (FWD) testing that improved design procedures can be developed to provide reliable and cost-effective HMA overlays for local roads.
Tom Winkelman, Local Planning and Programming Engineer in IDOT’s Bureau of Local Roads and Streets, served as Technical Review Panel (TRP) chair for the project during its final stages. Previous IDOT TRP chairs were Scott Lackey, District 5 Local Roads Engineer; and Kevin Burke, Local Policy and Technology Engineer.
The research team looked at three existing methods for determining HMA overlay thickness designs. According to Winkelman, “Those methods did not fully capture the existing pavement structural conditions when determining overlay thickness.”
A mechanistic–empirical method was therefore developed to better account for the condition of the existing pavement (see figure below).
“This new approach will allow local public agencies to design and implement more cost-effective HMA overlay solutions, and the results of this research will eventually be incorporated into Chapter 46 of the IDOT Bureau of Local Roads and Streets Policy Manual,” says Winkelman.
The study’s principal investigator was Erol Tutumluer, professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign and ICT Associate Director for Transportation Geotechnics. He says, “Pavement structural evaluation through nondestructive FWD testing is quite affordable in local road projects considering that 13 out of 20 pavement sections studied required lower thickness requirements when compared with those calculated by the current IDOT modified layer coefficients method. For the other 7 pavement sections, the developed mechanistic–empirical method safely assessed larger overlay thickness needs for a proper structural upgrade.”
Flowchart of the proposed mechanistic–
empirical overlay design procedure
Posted September 18, 2015