Use of Nuclear Gauge for Quality Control of an Unbound Base Course Blended with RAP

Abstract: In a recent study, it was found that the Virginia Department of Transportation (VDOT) could use up to 30% recycled asphalt pavement (RAP) in a pavement unbound base aggregate layer without any adverse effect on the pavement performance. To implement the use of RAP materials in the base course, an effective quality assurance protocol for monitoring construction is needed. Based on the recent study, a lightweight falling weight deflectometer (LWD) device was recommended to be used for quality control and quality assurance (QC/QA) of RAP-aggregate base construction. Currently, VDOT does not use such device for any of unbound layer construction control. A major modification of VDOT practices and significant resource allocations would be required to implement the LWD method for compaction control. As an alternative, this study explored the feasibility of using the nuclear gauge method, current VDOT practice for compaction control, to monitor the construction quality of a base course when up to 30% RAP is blended with base aggregate. Although several state DOTs currently use nuclear density gauge for such construction monitoring, accurate moisture measurement using nuclear device is challenging because of the presence of hydrogen in asphalt in RAP. A 2ft x 2ft wooden box was filled with RAP-aggregate blend at different proportions and compacted using a vibratory hammer in the lab. Densities were measured using nuclear density gauge and verified by Sand Cone test. Nuclear moisture measurements were compared to oven dry method and Speedy moisture tester. The nuclear gauge measured the wet densities accurately irrespective of RAP content in the base aggregate, with most measurements were within 5 pcf of the corresponding Sand Cone measurements in a laboratory set-up. Moisture measurements were affected by the presence of RAP and increased linearly with the increasing RAP content. Speedy moisture meter measurements were not affected by the presence of asphalt, however, the sample size affected the measurements, especially with higher RAP content, as more hydrophobic particles contributed to greater water content dispersion. Recommendations for the effective use of a nuclear gauge for quality assurance of unbound base aggregate blended with RAP were developed.