Analysis and Procedure for Conducting Laboratory Dielectric Measurements for Bulk Specific Gravity Determination

The use of a laboratory dielectric measurement system (LDMS), based on ground penetrating radar (GPR) technology, was explored in this study to alleviate the shortcomings (in terms of equipment, measurements and accuracy) of the current American Association of State Highway and Transportation Officials (AASHTO) specifications for measuring bulk specific gravity (Gmb) of laboratory compacted asphalt specimens. To ensure an accurate relationship between Gmb and dielectric measurements, repeatable and reliable testing using the LDMS is required. The objective of this study is to develop a procedure for conducting the LDMS. Collected dense-graded asphalt mixtures with a range of mixture properties (nominal maximum aggregate size, aggregate types, binder content, etc.) were compacted into asphalt specimens of various specimen surface conditions and sizes and tested using the LDMS. The collected dielectric results were statistically analyzed to study dielectric measurement repeatability and reliability by grouping measurements at various orientations together and comparing them to all measurements of the corresponding asphalt specimen. Sensitivity analysis was also performed to study measurement accuracy and resolution for replicate dielectric measurements. Taking dielectric measurements at any three orientations 120° apart (three measurements total) was determined to yield repeatable dielectric measurements with acceptable accuracy (maximum dielectric error of 0.04) for use as standard method for Gmb determination of compacted asphalt mixture specimens.