Performance of nonnuclear devices for in situ moisture and density determination

The largest portion of highway construction cost is in the earthwork phase. Inadequate soil subgrade compaction can cause structural failure of the roadway and infrastructure. Quality control of compacted soil subgrade is commonly performed using the nuclear density gauge. However, growing concerns over the safety of using the device with a radioactive source and training and calibration costs have warranted an effort to replace the nuclear density gauge. Several nonnuclear devices have been developed for the determination of in situ soil moisture density. These devices all utilize electromagnetic wave propagation theory to obtain frequency-dependent electrical measurements in a soil mass. These electrical measurements are subsequently related to soil properties such as moisture and density. Three of these devices were selected for this study to evaluate their performance and applicability for use in the field. The soil density gauge, electrical density gauge, and moisture and density indicator were examined at four construction sites to evaluate their reliability, repeatability, and usability under field conditions. In these tests, the density measurements of the devices were compared with densities obtained from a sand cone density apparatus and from a nuclear density gauge. Measurements of moisture content were compared with oven-derived moisture contents. Difficulties in device operation were also noted. This study found that the device based on electromagnetic impedance spectroscopy provided the most repeatable results and was easiest to use. Despite the criticism that its main algorithms are not accessible for user modification and site-specific calibration, this device appears to the most feasible device for replacement of the nuclear density gauge.