00615726

Component

http://onlinepubs.trb.org...trr/1991/1293/1293-003.pdf

https://scholar.google.co...iggs&publication_year=1991

Many highway agencies use falling weight deflectometers (FWDs) for pavement evaluation. The primary function of the FWD is to measure a deflection basin due to a load imparted to the pavement. Deflection basins measured in the field are used to backcalculate modulus profiles of pavement sections. Accurate determination of deflection basins in the field is critical. Velocity transducers (geophones) are used to determine the deflections, and load cells are used to measure the applied loads. The accuracy of deflections and loads obtained from these devices is of much concern, and a system is needed to calibrate them. A recently developed absolute calibration system is described. The system consists of two well-calibrated geophones, three load cells, a signal-conditioning unit, a loading plate, an analog-to-digital (A/D) board, and a computer. Software was developed to control the A/D board and to reduce the data. Geophones were selected for the calibration of the FWD sensors after an evaluation of the accuracy and precision of five candidate sensors. An aluminum loading plate was constructed to allow mounting of the load cells in line with and below the FWD load cell. The calibration curves of all load cells were traceable to the National Institute of Standards and Technology (formerly National Bureau of Standards). The effects on the calibration factors of load cells of using the aluminum plate were small. The signal-conditioning unit was developed to condition the signals before acquisition. The system was used to calibrate an FWD device. The system was effective. A calibration process is proposed on the basis of an analysis of the data collected. The calibration system is cost-effectve, accurate, and rugged, and it can be used by highway agencies to calibrate their FWD devices.

This paper appears in Transportation Research Record No. 1293, Backcalculation of Pavement Moduli 1991. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved

01411133

p. 24-30

1991

Transportation Research Record

0309051010

Figures (9) ; Photos (3) ; References (3) ; Tables (2)

Accuracy; Calibration; Deflection; Falling weight deflectometers; Geophones; Measurement; Nondestructive tests; Pavements

Design; Highways; Pavements; I22: Design of Pavements, Railways and Guideways; I23: Properties of Road Surfaces

TRIS, TRB, ATRI

Sep 30 1991 12:00AM

• ACCURACY AND CONSISTENCY OF BACKCALCULATED PAVEMENT LAYER MODULI
• ADVANCED BACKCALCULATION USING A NONLINEAR LEAST SQUARES OPTIMIZATION TECHNIQUE
• BACKCALCULATION OF ASPHALT CONCRETE-OVERLAID PORTLAND CEMENT CONCRETE PAVEMENT LAYER MODULI
• CALCULATING PAVEMENT DEFLECTIONS WITH VELOCITY TRANSDUCERS
• CHARACTERIZATION OF FALLING WEIGHT DEFLECTOMETER DEFLECTION BASIN
• COMPARISON OF COMPUTER PREDICTIONS AND FIELD DATA FOR DYNAMIC ANALYSIS OF FALLING WEIGHT DEFLECTOMETER DATA
• COMPARISON OF DYNAMIC AND STATIC BACKCALCULATION MODULI FOR THREE-LAYER PAVEMENTS
• DETECTION AND DETERMINATION OF DEPTH OF RIGID BOTTOM IN BACKCALCULATION OF LAYER MODULI FROM FALLING WEIGHT DEFLECTOMETER DATA
• EFFECT OF VARIOUS LOAD DISTRIBUTIONS ON BACKCALCULATED MODULI VALUES IN FLEXIBLE PAVEMENTS
• ESTIMATION OF PAVING MATERIALS DESIGN MODULI FROM FALLING WEIGHT DEFLECTOMETER MEASUREMENTS
• FULL-SCALE ACCELERATED PAVEMENT TESTING FOR THE TEXAS STATE DEPARTMENT OF HIGHWAYS AND PUBLIC TRANSPORTATION
• RELATING DEFLECTION DATA TO PAVEMENT STRAIN