Asphalt pavement compaction quality control and quality assurance (QC/QA) are traditionally based on destructive drilled cores and/or nuclear gauge results, which both are spot measurements representing significantly less than 1 percent of the in-service pavement. Ground penetrating radar (GPR) is emerging as a tool that can be used for nondestructive continuous assessment of asphalt pavement compaction quality through measuring the pavement dielectric constant. Previous studies have established that asphalt pavement dielectric constant measurements are inversely proportional to the air void content for a given asphalt mixture. However, field cores are currently required to calibrate the measured dielectric constant to the pavement density. In this paper, a method is proposed to eliminate the need for field calibration cores by measuring the dielectric constant of asphalt specimens compacted to various air void contents. This can be accomplished with a superpave gyratory compactor (SGC), which is routinely used in the pavement industry to fabricate 6 in. (15.2 cm.) diameter specimens. However, this poses difficulties with the GPR antenna height, direct coupling, and the Fresnel zone in relation to the asphalt specimen dimension limitation. These challenges are overcome by employing a plastic spacer with a known dielectric constant between the SGC specimen and the antenna. The purpose of the spacer is to reduce GPR wave speed so that the signal reflected from the specimen is separated from the direct coupling effects at an antenna height where the Fresnel zone of the GPR is not affected by the specimen dimension. The specimen dielectric constant can then be measured using the reflection coefficient-based surface reflection method (SR) or the pulse velocity-based time-of-flight method (TOF). Also, The Hoegh–Dai model (HD model) is demonstrated to reasonably predict pavement density based on the results of field measurements and corresponding core validation, especially as compared to the conventional exponential model. Results are presented from multiple days of paving on one project, as well as a single paving day on a project with significantly different mix properties. The agreement between the HD model, coreless prediction, and field cores shows the promise for implementation of dielectric-based asphalt compaction evaluation without the need for destructive field core calibration.

The behaviors of unbound aggregate base (UAB) and subgrade layers are considerably affected by seasonal moisture fluctuations which ultimately affect both their load-bearing capacity and the overall performance of the pavement structure. As part of an effort towards designing optimal performing pavements, this study was undertaken to evaluate, characterize, and quantify the effects of moisture and temperature variations on UAB and subgrade materials commonly used in Minnesota. The scope included analyses of subsurface moisture and temperature measurements and characterization of moisture variation in multiple instrumented pavement sections. Key findings indicated that dense-graded aggregate base materials with high quality crushed aggregates and lower fine particles were more resistant to seasonal moisture variations. By contrast, the subbase and subgrade materials exhibited considerable sensitivity to seasonal moisture variations. The subgrade layers, in particular, were found to operate in fully saturated conditions for more than half of their service life. Overall, the study results are a valuable contribution to establishing guidelines for laboratory testing and designing optimal performing pavement structures.

Ground penetrating radar (GPR) is gaining renewed attention from many state highway agencies because of its promising application prospects for rapid, full-coverage, continuous, and nondestructive measurements of the density in newly constructed asphalt pavements. However, several operational and technical issues need to be addressed before this technology can be efficiently deployed for quality control/quality assurance practices. The operation-related challenges are relatively easily addressed with proper project-specific management practices. The technical ones, on the other hand, require improvements to the testing devices and procedures and strategic investigations for further understanding of the relationship between the GPR-measured dielectrics and the density of asphalt mixtures. The latter is particularly crucial given the production and construction variability of asphalt mixtures and the accepted practices of field adjustments to mix designs. This study investigated the sensitivity of dielectric measurements to changes in mix composition and assessed the appropriateness (or lack thereof) of using a single dielectric-density transfer model to analyze field data measured on multiple production days. The study examined asphalt mixtures designed and manufactured in the laboratory with varying amounts of limestone, a high-dielectric aggregate source, as well as plant-produced asphalt mixtures collected on multiple production days. The findings indicated that the source/composition of the aggregate structure affected density-dielectric relationships of asphalt mixtures considerably. On the contrary, the relationship appeared to be less sensitive to normal asphalt production variability (day to day variations) as long as the aggregate source proportions were maintained intact. The experimental investigation proposed in this study can be easily employed to determine the proper amount of calibration models or the extent of allowable adjustment to the mix design for asphalt pavement construction projects.

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Pavement tenting, also referred to as crack-heaving, is a distress condition that primarily affects bituminous roads constructed in cold climates. This type of distress spreads over long stretches of roadways and can drastically affect drivers’ safety and comfort. The phenomenon occurs in freezing winter temperatures offering a limited and dire time window for testing. This paper discusses using an integrated multi-sensor non-destructive testing methodology to evaluate and characterize pavements affected by tenting. A survey van equipped with high-definition video and thermal cameras, LIDAR laser scanner, high-resolution accelerometer, and ground-penetrating radar (GPR) technologies was used to assess several roads suspected of tenting. The plurality of measuring devices and the data fusion and synchronization capabilities proved useful in revealing important pavement tenting characteristics that would have been otherwise overlooked. The data analysis led to the development of test parameters, derived from longitudinal profile measurements, that captured reasonably well the intensity and frequency of the tented cracks. The parameters were successfully employed to characterize the tested roads and determine the extent of critically affected segments. The study also showed the potential of GPR measurements to investigate underneath moisture conditions contributing to the formation of the tented cracks. Finally, the findings and tools developed in this study were discussed and compared with observations of local engineers who have extensive experience and insight on the subject matter. The knowledge and recommendations gathered in this final effort were also synthesized and incorporated into the paper.