Volume 3, Issue 3 (March 2006)
Assessing the Precision of Falling Weight Deflectometer for Field Measurements
Deflection-based techniques are being widely used to evaluate the structural integrity and for estimating the elastic moduli of in-service pavements. These deflections can be non-destructively induced and measured using various commercially available devices. In recent years, the Falling Weight Deflectometer (FWD) has gained worldwide acceptance among most highway agencies due to its versatility and ease of use. However, as with any testing using subject-driven, instrumented devices, the major concerns of the end usefulness of the resulting data are accuracy and precision. Although a level of uncertainty is always inherent to any measurement process, it must also be appropriately quantified or assessed. Therefore, the Florida Department of Transportation initiated the present field study to assess the level of precision of FWD measurements on flexible pavements. Deflection data were acquired using three FWD units concurrently on four different asphalt pavement sections. The precision was then addressed in terms of testing repeatability and reproducibility. In addition, the effects of buffer designs on deflection measurements were also evaluated. This paper presents a description of the testing program, data collection efforts, and subsequent analyses and findings. Precision statements for repeatability and reproducibility of field measurements were developed and are summarized herein. A generally high level of repeatability and reproducibility of the deflection measurements is demonstrated.