Experimental Study On The Long-term Performance And Optimizing Location Of FBG Sensors For Road Monitoring

With the development of economy, the high way is playing an increasingly important role indaily life. To ensure the normal operation, people need to keep abreast of the health and damageinformation of the high way. Considering all kinds of drawbacks of traditional detection techniques, areal-time health monitoring system is in serious need. FBG sensors have been gradually applied intraffic monitoring, and the service life of highway is up to ten years or even decades, thus, research onthe long-term performance of sensors embedded in pavements is of great significance.In this paper, two different packing materials and methods are used to encapsulate the baregrating to get rigid and flexible sensors which are signed as G and R respectively. The strainsensitivities of the sensors are determined through calibration test. Through embedding the sensors inSMA-13asphalt concrete specimen to conduct static loading calibration test and long-term dynamicloading test and conducting alternate freezing and thawing test to the sensors, a comprehensiveanalysis of the long-term performance of the sensors is obtained. Combining with the wheel trackinglateral distribution frequency curve, the optimum laying method of measuring vehicle speed andweight is obtained.The sensitivities of G sensors are1.492pm/με and1.552pm/με and the sensitivities of R sensorsare5.833pm/με and4.642pm/με respectively, which indicates that the sensitivities of these twosensors are higher than that of bare grating and the R sensor is of greater enhanced sensitivity. Thecenter wavelength and external load shows a good linear relationship after the sensors are embeddedin specimens. In the long-term dynamic loading test, the wavelength increases rapidly during earlyperiod, then continues to grow but with a slower rate during mid-term, and remains same at last. Afterthe long-term dynamic loading test, the center wavelength and load still remains a good linearrelationship with a near sensitivity. For G sensor, the effective working time under long-term dynamicload is254h, resistable rut time is6.4×105, which is equal to the service life of practical application inroad monitoring for3.92years. and for R sensor, the figure is240.5h and6.06×105respectively,which is equal to the service life of practical application in road monitoring for3.7years. The centerwavelength and load remains a good linear relationship before and after the long-term alternatefreezing and thawing test and the sensitivity barely changes, which indicates a good and stableperformance under low temperature condition.As for FBG sensors applied in road monitoring, the layout techniques are important aspects toresearch. In this paper, combined with the wheel track lateral distribution frequency curve, the optimum layout methods for vehicle speed and weight monitoring are obtained. By laying the sensorsin two rows with one single sensor in a row and several sensors in another, the vehicle speed andweight could be measured.