Seasonal variations in the moduli of unbound pavement layers

The in situ moduli of unbound pavement materials vary on a seasonal basis as a function of temperature and moisture conditions. Knowledge of these variations is required for accurate prediction of pavement life for pavement design and other pavement management activities. The primary objective of the present research is to advance the rational estimation of seasonal variations in backcalculated pavement layer moduli using data collected via the Seasonal Monitoring Program of the Long Term Pavement Performance Program. Principal components of this endeavor included: evaluation of the moisture predictive capabilities of the Enhanced Integrated Climatic Model (EICM); development of empirical models to predict backcalculated pavement layer moduli as a function of moisture content, stress state, and other explanatory variables; and trial application of the models developed to prediction backcalculated moduli for unbound pavement layers.; This investigation yielded two key contributions to advance the state-of-the-art of pavement engineering. First, it provided the impetus for developing EICM version 2.6 by demonstrating the practical inadequacies of EICM versions 2.0 and 2.1 when applied to the prediction of in situ moisture content, and then demonstrated that substantial improvement in the moisture predictive capability of the EICM had been achieved in Version 2.6. This contribution provided an immediate and direct benefit to the development of the forthcoming 2002 Guide for Design of New and Rehabilitated Pavement Structures. Second, the research identified fundamental shortcomings of linear layered elastic theory for modeling and evaluating nonlinear unbound pavement layers. The benefits of this finding are longer term, as additional research will be needed to develop nonlinear backcalculation models that are applicable in routine practice.; Other important findings included (1) variation in moisture content is not always the most important factor associated with seasonal variations in pavement layer moduli, and (2) the model form E/P_a = k ₁10(k2&thgr;/Pa)(τ/Pa+1)k3 fits linear elastic backcalculated moduli reasonably well.; The overall accuracy of the modulus predictions achieved in the trial application of the predictive models was not fully acceptable. Several avenues for further research to improve upon these results are identified.