Analysis of TransTech Model 300 Pavement Quality Indicator: Laboratory and Field Studies for Determining Asphalt Pavement Density

The pavement quality indicator (PQI) produced by TransTech Systems, Inc., uses principles of electrical impedance and the dielectric constants of materials to determine the densities of asphalt pavements. The Model 300 PQI device was recently evaluated in Illinois as a potential alternative to nuclear density gauges for quality control/quality assurance of asphalt pavement construction. Both laboratory and field testing were conducted to meet these objectives. The PQI has several appealing features relative to the nuclear density gauge, including its light weight and rapid operation in the field without the need for special licensing, handling, or training. The density determined with the nuclear density gauge generally exhibited a closer correlation with the density determined from pavement cores, as denoted by significantly lower squared error of the regression values in the regression analyses performed. Also, although the Model 300 PQI has been improved from earlier models to account for moisture and temperature, the data suggest that the device is still influenced by environmental conditions. On the other hand, the PQI proved to be more operationally convenient for the field technician, being significantly lighter and less time-consuming to operate in the field. On the basis of analysis of the information obtained from the studies, the Illinois Department of Transportation has chosen to base acceptance and statistical pay factors on density values obtained by the AASHTO T166 method with pavement cores. At present, the nuclear density gauge is still the specified device for quality control/quality assurance of asphalt pavement projects in Illinois.