Asphalt Concrete Density’s Monitoring during Construction

Over the past three decades, GPR has been implemented for various applications in civil engineering infrastructure, including predicting in-situ density of AC pavements. Given the sensitivity of asphalt concrete (AC) layer density to compaction effort during construction, real-time AC density monitoring is invaluable. Unlike traditional approaches that estimate in-situ AC density (e.g., extracted cores and nuclear gauge measurements), ground penetrating radar (GPR) technology may be used for real-time prediction of AC density, allowing modification of compaction pattern and effort on the fly. A new GPR mount prototype was designed, allowing direct installation on various roller compactor types. The design was field validated.

Electromagnetic mixing theory is used, and bulk AC dielectric constant is related to its components’ dielectric constants and their corresponding volumetric proportions. The AC volumetrics could be determined from the job mix formula. The relative dielectric constants of binder and air are known to be approximately 3 and 1, respectively. However, cores are usually required to back-calculate the aggregates’ dielectric constant, which depends on aggregate minerology. In this study, aggregate dielectric constant values were used from an established aggregate dielectric constant database for Illinois.

Six stone matrix asphalt (SMA) test sections were constructed using different aggregate types at the Illinois Center for Transportation. GPR data were collected for each roller pass during compacting the test sections. An automated density prediction tool was developed to provide the roller operator with real-time prediction of the AC density. The AC predicted densities were compared to values obtained from nuclear gauge measurements and extracted cores densities. The GPR-predicted AC densities were better correlated to ground truth core densities than those by a nuclear gauge. In addition to ensuring AC quality when the introduced system is used, cost savings and emission reduction could be realized when compaction effort is optimized.