The Use of Falling Weight Deflectometer Data in Monitoring Flexible Pavement Systems

Abstract

Pavement performance studies are being conducted in the states of Nevada and Washington for the purpose of developing mechanistically based pavement design procedures for highways. A critical element of each of these studies is the statewide characterization of the pavement materials. The materials characterization process has included laboratory and field testing for 16 sites in Washington and 27 sites in Nevada. This paper presents the general approach used by these states in the development of mechanistic design methods and how resilient moduli inferred from falling weight deflectometer (FWD) data have been used in the process. The FWD has been used to monitor the variability of roadway materials and to ascertain the seasonal changes in material properties. Comparisons of laboratory-determined and field-estimated resilient moduli are discussed. It was found that there is generally excellent agreement between the laboratory and field results on subgrade modulus. The accuracy of granular base course modulus estimates primarily depends upon the thickness of the base course and the thickness of the asphalt concrete surface. Backcalculated asphalt concrete modulus values can differ significantly from laboratory values. However, if care is taken to account for the effects of temperature and rate of loading, the agreement for uncracked asphalt concrete can be good. One of the important assets of the FWD is that it allows the evaluation of in-place materials variations. Thus, it is possible to realistically sample and test materials for design purposes. This, in turn, means that material properties can be treated more realistically than they have been in the past. In the development of a mechanistically based pavement design procedure, it is necessary to account for seasonal variations in material properties. The FWD can be used for the purpose of monitoring how materials change with the environment. This information can be used to develop algorithms which describe these changes. Washington State has accumulated over two years of data regarding seasonal changes, and Nevada has just begun to gather these data. This paper presents the approaches used by these two states in the development of pavement design procedures. It is hoped that the information contained herein will be of use to others considering similar efforts.