Moisture effects on moduli of pavement bases

Mechanistic-Empirical (ME) pavement design approaches consider seasonal moisture variations in the subgrade and unbound aggregates base (UAB) layers as an important design parameter. Understanding such moisture variation is essential for modelling the pavement section and predicting its performance. The Enhanced Integrated Climate Models (EICM) are often used to predict the moisture contents in the UAB and subgrade layers for different seasons so that the resilient moduli of the layers can be adjusted. This paper provides an in-depth analysis of the moisture effects on the moduli of a UAB material with four different gradations. Commonly used laboratory and field-testing methods were conducted to measure the moduli of the specimens prepared at different moisture contents and fine contents from the same UAB source. The UAB moduli decreased with the increase in the moisture content. However, the patterns in the reduction in modulus depended on the laboratory or field test method used. Although the EICM module of the AASHTOWare Pavement ME Design software can predict the laboratory resilient moduli at moisture contents greater than the optimum moisture content, it was not possible to measure the moduli at those elevated moisture contents for the selected UAB.