Evaluating Nonnuclear Measurement Devices to Determine In-Place Pavement Density

The air void content of both in-place and laboratory-compacted hot-mix asphalt may be the factor that most affects the performance of a properly designed mixture. A mediocre mix, well constructed with good in-place air voids, often will perform better than a good mix that has been poorly constructed. In-place density may be monitored by using three methods: cores, nuclear density gauge measurements, and nonnuclear density gauge measurements. A study was done to evaluate and compare two non-nuclear density devices, the pavement quality indicator (PQI) Model 301 and the PaveTracker, to in-place core densities. Testing and analyses of 20 projects showed that uncorrected gauge measurements (from each gauge) provided reasonable correlation (significant at a 5% level of significance) with core density measurements approximately 75% of the time. Average coefficients of determination for the relationships between uncorrected gauge measurements and core densities were approximately .5. Simulation analyses indicated that the error in measuring in-place air voids using calibrated PQI Model 301 gauge measurements based on the constant offset method can be 1% to 2.7% air voids for the average of 10 measurements. The numerical experiments also indicated that calibration of PQI Model 301 by simple offset or by slope and offset did not improve the correlation between the gauge and core densities.