Development Of Helical-Bending Optical Fiber Strain Sensor And Its Application In Pavement Engineering

Optical fiber sensing technology is a new sensing technology developed along with fiber optic and optical communication technologies.Compared with traditional electrical sensing technology,optical fiber sensor has significant advantages in harsh road construction and service environments.In this research,in order to enlarge the measurement range of the optical fiber sensor and reduce the cost of the sensor,an optical fiber strain sensor based on the optical helical winding modulation structure is developed.The sensor system consists of optical fiber sensing elements,a packaging structure,a quasi-distributed measurement network and a signal demodulation algorithm.Based on dynamic simulations of the sensor responses under rolling compaction of asphalt concrete and 3D printing technology,a sensor for deformation monitoring of asphalt pavement is developed.The performance of the sensor was verified by laboratory and field experiments.The deformation data of the asphalt mixture compaction process is obtained.The main research developments of this study are summarized as follows.(1)Based on the principle of macro-bending loss of optical fibers,the influence of helical bending structure on the optical loss index of optical fibers is assessed.The data file processing program of optical time domain reflectometer was developed using Matlab.,The noise distribution and of the measured signal was analyzed and a denoising method was developed to improve the signal-to-noise ratio of the sensor.(2)Based on the helical-bending modulation structure of optical fibers,a prototype of fiber optic strain sensor based on rubber rod is developed.The optimal pitch and mechanical properties of rubber materials of the sensor were analyzed and a signal demodulation method was developed.Through data analysis and calibration test,the factors that may affect the sensing performance of the helical-bending structure are analyzed,which provides guidance for the parameter selection of the measuring equipment and improves the sensing performance.The quasi-distributed multiplexing method and the demodulation method of the sensor are evaluated and utilized.Uses of these methods improve the measurement range of the sensor and expand the application scenarios of the sensor.(3)Based on a viscoelastic constitutive model,the ABAQUS finite element software is used to simulate the dynamic compaction process of hot asphalt mixture,and the deformation characteristics of the compaction process of asphalt concrete mixtures are obtained.According to the characteristics of compaction deformation of asphalt mixture,using a cylindrical spring replacement rubber rod as elastic substrate,a sensor for deformation monitoring of asphalt pavement is developed.The influencing factors on strain measurement sensitivity of the sensor are analyzed by theoretical calculations,Matlab simulations and finite element analyses.Based on the analysis results,the geometric parameters of the spring were optimized,which effectively improves the sensitivity of the sensor.(4)A quasi-distributed sensing network with three sensing nodes was built.The quasi-distributed sensing network was used to monitor the compaction process of asphalt mixture.The experimental data show that the vertical deformation of as-phalt mixture increases gradually with the increase of compaction times,and finally tends to be stable.The sensor monitoring of experimental compaction processes indicated that the sensor can monitor the compaction process of asphalt mixture.In brief,in this study,a large-strain optical fiber sensor based on the principle of optical fiber macro-bending loss and using the helical-bending modulation structure is developed.Compared with commercial fiber sensing technologies,the strain sensing range of the newly developed sensor is greatly enlarged.The sensor has advantages of simple structure,low cost and flexibility for customization.Based on these basis preparations,a sensor for deformation monitoring of asphalt pavement is developed and it provides a novel monitoring method to understand the compaction mechanisms and improve the quality of asphalt concrete pavement construction.It provides a new scope of applications of large-strain fiber optic sensors.