Critical Factors Affecting Field Determination of Hot-Mix Asphalt Density Using Nonnuclear Devices

Abstract

Nonnuclear methods for the measurement of hot-mix asphalt (HMA) density offer the ability to take numerous density readings in a short time period, without the need for intensive licensing, training, and maintenance efforts common to nuclear gauges. The Pavement Quality Indicator (PQI) and the PaveTracker use electrical impedance to estimate density. Early models of these gauges were deemed inadequate for quality control and quality assurance testing, but improvements have been made to each. In this project, a ruggedness study was performed to evaluate the effects of gauge model, temperature, moisture, use of sand to fill surface voids, gauge orientation, number of replicate measurements, and gauge placement on two nonnuclear gauges. Significant factors arising from the ruggedness study were further investigated. Two 12.5-mm mixes and one 37.5-mm mix were evaluated, using 42 test locations. Gauge orientation was significant, suggesting that the test method protocol should specify gauge orientation with respect to the direction of paving. Four replicate measurements were deemed acceptable for producing a single reported result, and all sand and debris should be thoroughly brushed from the surface before testing. Moisture significantly affected the measured densities in some cases, most notably for the 37.5-mm test locations and for the PaveTracker device.