Development of an improved calibration procedure for the electrical density gauge

The nuclear density gauge (NDG) is currently the state-of-The-practice device used for quality control of compacted subgrade materials used in transportation construction. However, many transportation agencies have growing concerns over these devices because of the increasingly stringent storage and maintenance requirements of a device with a radioactive source, and with the costs associated with personnel training. These concerns have led to the development of non-nuclear devices as potential replacements for the NDG. The Electrical Density Gauge (EDG) is a non-nuclear device that calculates the dry unit weight and moisture content of soil by means of electromagnetic wave propagation theory. The device requires a soil-specific calibration process where soil moisture and density are correlated to electrical parameters. These correlations are referred to as soil models. Unfortunately, the manufacturer recommended procedure tends to be cumbersome and very labor-intensive. This paper presents a new, less labor-intensive calibration procedure. Calibrated soil models were generated using the manufacturer recommended procedures and the new proposed procedures. Models were then tested for accuracy using a large soil test box, which simulated field conditions. In general, it was found that the new procedures outperformed the manufacturer recommended procedures.