Estimation of Air Void Content of Dense Graded Water-covering Asphalt Layer Based on GPR
CUI Lilong1, LING Tianqing2, ZENG Fangui3, LIANG Lijuan4, LI Rukai1
1 College of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China 2 College of Architecture and Urban Planning, Chongqing Jiaotong University, Chongqing 400074, China 3 Chongqing Construction Residential Engineering Co., Ltd, Chongqing 400015, China 4 Guiyang Urban Development & Investment (Group) Co., Ltd, Guiyang 550000, China
Abstract: In order to solve the problem that ground penetrating radar (GPR) can not predict the air void content of water-covering asphalt layer with metal plate reflection method, three kinds of FDTD numerical models of pavement structure with different incident angles of pulse are established to study the influence of the dispersion of pulse on the reflection coefficient of monochromatic wavelet. Under the assumption of dry-wet layers system, a nonlinear calculation algorithm is proposed based on the theory of full waveform inversion with the considering of the incident angle of pulse. The dielectric constant and air void content of dry asphalt layer can be obtained through the nonlinear calculation algorithm utilizing GPR when the surface of layer is covered water. The reliability of the algorithm is validated by employing FDTD numerical models of dry-wet layers system with seven different moisture contents as well as the laboratory test. The results show that in the range of incidence angle of three numerical models, the variation of reflection coefficient of monochromatic wavelet is very small, which can be regarded as a constant, meaning the excitation value of incident wavelet corresponding to each frequency is the same. The synthetic pulse reconstructed by nonlinear calculation algorithm match the real wave well. The error of dielectric constant estimated by metal plate reflection method and nonlinear calculation algorithm increases with the rising of moisture content of wet asphalt layer, while the error growth of nonlinear calculation algorithm is much smaller than that of metal plate reflection method. Compared with the metal plate reflection method, the relative error of the dielectric constant, the bulk specific density of asphalt mixture and the air void content obtained by the nonlinear calculation algorithm are reduced from 10.9% to 1.6%, from 4.6% to 1.1%, and from 24.9% to 7.2%, which proves the nonlinear calculation algorithm can effectively eliminate the influence of water covering on the asphalt layer to calculate the dielectric constant and air void content of dry asphalt layer accurately, providing an accurate and effective way for the real-time monitoring of asphalt layer compaction quality and intelligent compaction technology.
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