AASHTO R 32-20 PDF Download

The AASHTO R 32-20 standard is a recommended practice for calibrating the load cell and deflection sensors on a falling weight deflectometer (FWD). The standard specifies the procedures for both the annual calibration of the load cell and deflection sensors and the monthly relative calibration of the deflection sensors.

The calibration process involves establishing calibration factors that can be used to correct FWD measurements. A certified technician is required for the annual reference calibration, which is performed once a year or when the load cell has been replaced. The monthly relative calibration can be performed by any technician and should be done at least once a month or immediately after a deflection sensor is replaced.

The calibration factors obtained from the calibration procedure are entered into the FWD software as multipliers, allowing the correction of the FWD measurements to align with the calibration instrumentation. The procedure is applicable to various types of FWDs with minor modifications, and it is recommended to use the automated software package called WinFWDCal to carry out the calibration procedure.

In order to use the procedure, the FWD computer must be capable of electronic data transfer, and data files from all types of FWDs can be read by the WinFWDCal software. The PDDX file format is required for data input, and if the FWD data files are in their native format, they can be converted to PDDX format using the PDDXconvert tool within the WinFWDCal software package.