PURPOSES: The objective of this study was to determine the relationship between the dielectric characteristics of asphalt mixtures and the air voids present in them using ground penetrating radar (GPR) testing.
METHODS : To measure the dielectric properties of the asphalt mixtures, the reflection coefficient method and the approach based on the actual thickness of the asphalt layer were used. An air-couple-type GPR antenna with a center frequency of 1 GHz was used to measure the time for reflection from the asphalt/base layer interface. A piece of aluminum foil was placed at the interface to be able to determine the reflection time of the GPR signal with accuracy. An asphalt pavement testbed was constructed, and asphalt mixtures with different compaction numbers were tested. After the GPR tests, the asphalt samples were cored and their thicknesses and number of air voids were measured in the laboratory.
RESULTS: It was found the dielectric constant of asphalt mixtures tends to decrease with an increase in the number of air voids. The dielectric constant values estimated from the reflection coefficient method exhibited a slight correlation to the number of air voids. However, the dielectric constant values measured using the approach based on the actual asphalt layer thickness were closely related to the asphalt mixture density. Based on these results, a regression equation to determine the number of air voids in asphalt mixtures using the GPR test method was proposed.
CONCLUSIONS: It was concluded that the number of air voids in an asphalt mixture can be calculated based on the dielectric constant of the mixture as determined by GPR testing. It was also found that the number of air voids was exponentially related to the dielectric constant, with the coefficient of determination, R2, being 0.74. These results suggest that the dielectric constant as determined by GPR testing can be used to improve the construction quality and maintenance of asphalt pavements.

1. 서론
 2. 유전상수 산정 방법
 3. 유전상수와 공극률의 관계에 대한 기존문헌 고찰
 4. GPR 시험을 위한 테스트베드 시공
 5. 시험 결과
 6. 결론
 REFERENCES

• 김제원(한국건설기술연구원 도로연구소 수석연구원) | Kim Je Won
• 김연태(한국건설기술연구원 도로연구소 전임연구원) | Kim Yeon Tae
• 김부일(한국건설기술연구원 도로연구소 연구위원) | Kim Booil
• 박희문(한국건설기술연구원 도로연구소 연구위원) | Park Hee Mun 교신저자