History and Development of U.S. Procedures for Falling Weight Deflectometer Calibration

Abstract

In 1988 the Strategic Highway Research Program purchased four falling weight deflectometers (FWDs). During the acceptance testing it became evident that an improved procedure for calibration was needed to determine whether the specifications for the precision and the accuracy of the sensors were achieved. The authors were responsible for developing the procedure. This paper reports on the steps taken during the development of the calibration protocol. The reasons underlying the equipment and the procedures chosen are discussed. The sources of error in FWD measurements are identified, and ways that have been used to reduce those errors are reported. The goal was to reduce the systematic (bias) error to less than 0.3% through calibration. This level of error ensures that the random measurement error is larger than the systematic error for all pavement deflections less than 600 μm [24 mils (1 mil = 0.001 in.)]. Experience has shown that most highway pavements deflect less than 600 μm. The effects of FWD measurement errors on backcalculated pavement moduli are briefly reviewed. Verification of the protocol by several means showed that the calibration goal was achieved. Subsequent experience with the calibration protocol has shown that it has been effective and that it ensures high quality in the FWD data.

Get full access to this article

View all access options for this article.

References

Richter

C. A.

, and Rauhut

J. B.

. SHRP Plans for Nondestructive Deflection Testing in the Development of Pavement Performance Prediction Models. In Nondestructive Testing of Pavements and Backcalculation of Moduli. ASTM STP 1026 ( Bush

A. J.

III , and Baladi

G. Y.

, ed.), ASTM, Philadelphia, Pa., 1989, pp. 556–562.

Irwin

L. H.

, Yang

W. S.

, and Stubstad

R. N.

. Deflection Reading Accuracy and Layer Thickness Accuracy in Backcalculation of Pavement Layer Moduli. In Nondestructive Testing of Pavements and Backcalculation of Moduli. ASTM STP 1026 ( Bush

A. J.

III , and Baladi

G. Y.

, ed.), ASTM, Philadelphia, Pa., 1989, pp. 229–244.

SHRP FWD Calibration Protocol. In Manual for FWD Testing in the Long-Term Pavement Performance Program, SHRP, National Research Council, Washington, D.C., 1993, pp. A1–A22.

Standard Specifications for Transportation Materials and Methods for Sampling and Testing, Part 1B: Specifications, 24th ed. AASHTO, Washington, D.C., 2004, pp. R321 and R331.

Orr

D. P.

, and Wallace

J. M. S.

. Falling Weight Deflectometer Calibration: Looking Back to the Future. In Pavement Evaluation 2002 (CD-ROM), Virginia Polytechnic Institute and State University, Roanoke, 2002.

Fulfilling the Promise of Better Roads: A Report of the TRB Long-Term Pavement Performance Committee. TRB, National Research Council, Washington, D.C., 2001.