A FIELD EVALUATION OF NUCLEAR GAUGE CALIBRATION METHODS, PART 1: MANUFACTURER'S CALIBRATION

A field evaluation was made of several methods of calibrating nuclear density/moisture gauges. Wet densities, moisture contents and dry densities of a layer of crushed rock pavement were determined by four gauges at 40 sites using the manufacturer's blocks calibration. Subsequently the corresponding orthodox test values were measured by the sand replacement and IPCAD tests. In part 1 of this two part series, the accuracy of results obtained by the manufacturer's blocks method of calibration is discussed. It is concluded that the use of this type of calibration can result in substantially biased estimates of orthodox wet densities, moisture contents and dry densities. Significant differences were also observed between the results of gauges when calibrated by this method. Consequently when specifications are based on gauge rather than orthodox test values, more reproducible results would be obtained if all gauges involved in testing were adjusted to give similar results (a). (TRRL)