Non-nuclear methods for HMA density measurements : final report, June 2008.

Final report; June 2008PDFResearch PaperMBTC 2075Measuring instruments by techniqueHot mix paving mixturesDensityAsphalt mixturesArkansasUniversity of Arkansas, Fayetteville. Dept. of Civil EngineeringWilliams, Stacy G.University of Arkansas, Fayetteville. Dept. of Civil EngineeringNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsNTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and PerformanceUS Transportation CollectionNon-nuclear methods for the measurement of hot-mix asphalt (HMA) density offer the ability to take numerous density readings in a very short period of time, without the need for intensive licensing, training, and maintenance efforts common to nuclear gauges. The Pavement Quality Indicator\ue2\u201e\ua2 (PQI) and the PaveTracker\ue2\u201e\ua2 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 number of field sites were used to evaluate the non-nuclear gauges in terms of ruggedness, accuracy, and precision. A thorough investigation of calibration methods was also performed.In the ruggedness study, three pavement sites were used to determine potential procedural factors that significantly affected the non-nuclear density results. Moisture, the presence of sand or debris, gauge orientation, gauge type, and presence of paint markings were determined to significantly impact the accuracy of non-nuclear gauge readings.Four calibration methods were investigated, including screed offset, core offset, two-point, and data pair techniques. None were found to possess all of the necessary components for generating significant correlations with field core densities. A screed-core method was developed as a method to more comprehensively adjust the magnitude of the offset as well as the sensitivity of the device over a large range of true densities.Overall, neither non-nuclear gauge was able to predict core densities as accurately or precisely as the nuclear gauge. Of the non-nuclear devices, the PQI generated more consistent results but was less sensitive to actual changes in density. The PaveTracker was more sensitive to actual changes in density, but exhibited a higher level of variability. Existing specifications for use of non-nuclear devices should be edited to include guidance on gauge orientation during testing, as well as calibration procedures for a screed-slope type of technique