The effect of seasonal variations on the resilient modulus of unbound materials

Pavement design continues to advance from empirical towards mechanistic methodologies. A project to develop guidelines for the implementation of the new mechanistic-empirical pavement design guide (ME PDG) for Canadian conditions has been advanced through the Pavements and the Soils and Materials Standing Committees of the Transportation Association of Canada (TAC). This project will identify the needs for the calibration and validation of the M-E Pavement Design Guide for conditions typical for Canada. Material characterization for input into the ME PDG will be a principle component of data collection activities. More specifically, the major material characteristics associated with unbound materials will quantify stress state and in-situ moisture conditions. Typically, the moduli of coarse-grained materials will increase with the confining stress, while cohesive materials may have a reduction in moduli. Further, the moduli will generally decrease with increases in-situ moisture contents as can be expected with seasonal climatic variation. A study has been undertaken to examine how subgrade material characterization can be better quantified, especially given that seasonal variations in the Canadian climate have a huge impact on test results. The recently constructed Centre for Pavement and Transportation Technology (CPATT) test track, located at the University of Waterloo provides a readily accessible, safe, and relatively uniform location for determining the seasonal variations of Mr in the unbound layers. The road consists of five different asphalt mix test sections, each approximately 140 m in length constructed over dense graded granular base and a predominantly clay subgrade. In the Fall of 2003, CPATT in collaboration with ARA began a non-destructive deflection testing program to complete pavement load/deflection testing and data analysis of the test track at regular intervals. The primary objective of this work is to compile a database of seasonal variations to the Mr of the unbound layers, which could subsequently be used in the ME PDG calibration. This paper outlines the testing program used to collect the pavement load/deflection data and presents the test results collected to-date.