Mn/ROAD Case Study Using CalBack and CalM

This study demonstrates how the software programs CalBack and CalME were used to predict the in-situ pavement performance of two test sections at the Minnesota Road Research Project (Mn/ROAD). The study demonstrates the benefits of using CalBack to backcalculate changes in layer moduli from deflection data; the resulting data show the influence of freeze/thaw and seasonal changes of subgrade stiffness; the confining effects of overlying layers; and the hardening/aging effects of time on the hotmix asphalt (HMA). Data from the comprehensive Mn/ROAD database were used to run CalME, a program that simulates pavement performance using a mechanistic-empirical approach. These inputs included data collected on traffic and environment, from condition surveys, and during falling weight deflectometer and material testing. Two mainline flexible pavement cells—Cell 3 and Cell 21—were selected for the study for two reasons: because of the availability of material for laboratory testing by the UCPRC to characterize material response/performance models for CalME simulation, and because of the cells’ contrasting pavement performance with respect to fatigue cracking and rutting. For both cells, the CalME simulations, which presumed bottom-up fatigue cracking, matched reasonably well with the top-down cracking indicated by the condition survey. Whether the cracking resulted from a bottom-up or top-down process remains an open question. CalME accurately predicted the rutting performance of Cell 3 appropriately; however, the rutting performance of Cell 21 did not match well with the software’s predicted results, although possible over-asphalting during construction or the Marshall mix design might have contributed to premature rutting failure. Overall, the use of CalBack and CalME for predicting pavement performance for this climate (cold winter, warm summer) appears promising. However, the CalME performance shift factor for rutting, developed from HVS testing, appears to need recalibration for normal traffic.