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Publication Number: FHWA-HRT-04-079
Date: July 2006
Seasonal Variations in The Moduli of Unbound Pavement Layers
Chapter 1: Introduction and Research Objectives
Among the more important considerations in pavement design is the fact that the in situ moduli of the pavement layers vary on a seasonal basis, due to variations in the environmental conditions within the pavement structure. For the sections under study in the Seasonal Monitoring Program[ 1 ] of the Long-Term Pavement Performance (LTPP) program, the observed amplitude of seasonal variations in backcalculated moduli for unbound pavement layers, exclusive of frost effects and expressed as a percentage of the minimum observed modulus, ranges from 1 percent to more than 300 percent.
Seasonal variations in pavement layer moduli are important because the deflections, stresses, and strains induced in the pavement by traffic loads, and the resultant incremental damage imparted to the pavement, vary with the moduli of the pavement layers. Unlike most structures, pavements are designed with a finite life expectancy, with design lives greater than 25 to 35 years being the exception, not the rule. The key to cost-effective management of a network of pavements lies in the ability to predict the condition of each pavement at any selected time, and when each will fail (i.e., performance) with a reasonable degree of accuracy and precision. This cannot be achieved without considering the seasonal variations in the pavement layer moduli, and resultant variations in incremental damage.
The work discussed here applied data collected through the Seasonal Monitoring Program of the LTPP program to study the issue of seasonal variations in unbound pavement layers, exclusive of frost effects. Within the Seasonal Monitoring Program, data characterizing both the structural changes in the pavement and the key factors believed to cause those changes are collected monthly. Selected site-specific weather data are collected continuously. The test sections at which these data are collected are geographically dispersed and thus represent a broad array of temperature and moisture conditions prevalent in the United States. Details of test sections and the data used in this investigation are provided in Chapter 3.
The overall goal of this research was to advance the state of the art relative to the estimation of seasonal variations in backcalculated pavement layer moduli for unbound pavement materials under nonfrozen conditions. Four specific objectives, elaborated in the next section, support that goal:
This study applied data collected via the Seasonal Monitoring Program of the LTPP program to build upon the foundation embodied in the EICM for the prediction of backcalculated pavement layer moduli for unbound pavement layers under nonfrozen conditions. The overall research approach was comprised of four major tasks:
Overall conclusion and recommendations drawn from this study are presented in Chapter 7.