Evaluation of Unbound Aggregate Base Layers using Moisture Monitoring Data

Abstract

The behaviors of unbound aggregate base (UAB) and subgrade layers are considerably affected by seasonal moisture fluctuations which ultimately affect both their load-bearing capacity and the overall performance of the pavement structure. As part of an effort towards designing optimal performing pavements, this study was undertaken to evaluate, characterize, and quantify the effects of moisture and temperature variations on UAB and subgrade materials commonly used in Minnesota. The scope included analyses of subsurface moisture and temperature measurements and characterization of moisture variation in multiple instrumented pavement sections. Key findings indicated that dense-graded aggregate base materials with high quality crushed aggregates and lower fine particles were more resistant to seasonal moisture variations. By contrast, the subbase and subgrade materials exhibited considerable sensitivity to seasonal moisture variations. The subgrade layers, in particular, were found to operate in fully saturated conditions for more than half of their service life. Overall, the study results are a valuable contribution to establishing guidelines for laboratory testing and designing optimal performing pavement structures.