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Publication Number: FHWA-RD-94-110
Date: January 1995
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This report describes the operation theory, installation procedures and operation guidelines for instrumentation selected to monitor changes in internal pavement moisture and thermal regimes, frost/thaw conditions, and external climate at test sections in the long-term pavement performance seasonal monitoring study. The instrumentation includes time domain reflectometry to measure moisture content of unbound materials, thermistor sensors to measure pavement temperature gradients and air temperature, electrical resistivity probes to measure frost locations, a piezometer to measure the depth of ground water table and tipping-bucket rain gauge to measure precipitation. These measurements of the external climate and the resulting changes in the pavement material will be coupled with monthly or more frequent deflection measurements, seasonal roughness measurements, elevation profile and distress surveys to study the cause and effects of seasonal changes in pavement structural response. Guidelines and procedures for the collection of these data are also described in this report.
It is widely recognized that temperature, moisture, and frost/thaw related changes in pavement structures, both within a day, and over the course of a year, can have a significant impact on structural characteristics of pavement layers, thereby affecting response of the pavement to traffic loads, and ultimately the life of the pavement. However, the magnitude and relationship of these effects are not well understood, making them difficult to address (with any degree of accuracy or confidence) in pavement design and evaluation.
The Seasonal Monitoring Program (SMP) within the long-term pavement performance (LTPP) study intends to begin to rectify this situation. Products of the LTPP seasonal monitoring effort will provide (1) the means to link pavement response data obtained at random points in time to critical design conditions; (2) the means to validate models for relationships between environmental conditions (e.g., temperature and precipitation) and in situ structural properties of pavement materials; and (3) expanded knowledge of the magnitude and impact of the changes involved.
This manual was developed for use by personnel responsible for installing moisture, temperature and frost/thaw instrumentation, and collecting data in pavement test sections in the seasonal monitoring program. The manual presents an overview of the seasonal monitoring instrumentation, provides guidelines for the installation and operation of this instrumentation, and provides guidelines for the collection of seasonal monitoring data.
People involved with seasonal monitoring are encouraged to discuss the contents of this manual with the four LTPP Regional Coordination Office Contractors (RCOC's). The RCOC's will keep FHW A-LTPP Division staff informed of necessary changes. Periodic review and necessary updates to the manual will help keep the guidelines current and maintain uniform installation and monitoring procedures among the four regions.