Impact of Local Calibration on Rehabilitation Design: Comparison of Mechanistic–Empirical and AASHTO 1993 Methods in Michigan

Abstract: The Michigan Department of Transportation (MDOT) is currently conducting a comprehensive study to locally calibrate the mechanistic–empirical performance prediction models in AASHTOWare Pavement Mechanistic–Empirical Design (PMED) for pavement rehabilitation applications. As part of this ongoing effort, the research team evaluated the impact of the newly calibrated models on rehabilitation design outcomes in comparison with the current AASHTO 1993 procedure. The team selected representative pavement sections from MDOT’s life-cycle cost analysis (LCCA) database and used identical PMED input parameters to ensure a rational comparison. The study focused on five rehabilitation categories, including hot-mix asphalt (HMA) over HMA, HMA over crush and shape (C&S) HMA, HMA over rubblized PCC, HMA over PCC/composite (HMA/PCC), and unbonded PCC overlays. For the C&S, rubblized, and unbonded overlays, both the newly developed calibration coefficients and the previous SPR-1595 coefficients were used for comparison. In contrast, HMA over HMA and HMA over composite sections were evaluated using the locally calibrated coefficients only.
Preliminary findings suggest that the locally calibrated PMED models yield overlay thicknesses that are generally comparable to, but less conservative than, those obtained using the AASHTO 1993 method. For C&S sections, PMED designs ranged from 3.5 in. to 4.0 in. compared to 6.5 in. for AASHTO 93, with thermal cracking controlling most cases. For rubblized sections, the new and old calibrations yielded thicknesses between 6.5 in. and 7.5 in., consistent with AASHTO 93 results. Composite overlays were typically 0.5 in. to 1.0 in. thicker than AASHTO designs, governed by total transverse cracking. HMA over HMA designs yielded a minimum thickness of 3.5 inches, which is less than the AASHTO 93 design. The JPCP-based coefficients, derived from a larger calibration dataset, yielded more reasonable and consistent overlay thicknesses for unbonded overlay designs.