Sensing Performance and Optimizing Encapsulation Materials of a Coordinated Epoxy-Encapsulated Sensor for Strain Monitoring of Asphalt Pavement Layered Structures

The accurate mechanical response of asphalt pavement interlayer structure under complex environments still lacks reliable and durable real-time monitoring methods up to now. In this study, metal-foil strain gage, a mature and traditional stickup sensing element, was innovatively used as an embedded strain sensor to monitor asphalt mixture deformation by proposing the method of polymer encapsulated strain gage. The performance of encapsulating polymer was optimized and the effectiveness of sensor was studied. The DMP-30 was adopted to modify epoxy
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anhydride blends for strain gauge encapsulation, and dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy were carried out. The results indicated that the encapsulating polymer with 1phr DMP-30 shows good modulus accommodation with asphalt pavement, and provides better thermal properties to adapt to the harsh environment of pavement monitoring. Benefiting from the encapsulated method and optimized encapsulating polymer, the sensor shows the same excellent sensing performance as the bare strain gage as well as good linearity and fatigue performance (more than 100,000 cycles at 200u
$\varepsilon $
). Laboratory bending test of asphalt concrete with embedded sensor verified the high sensitivity coefficient and good survivability, which is accurate for micro strain monitoring. Meanwhile, numerical simulation confirmed the good compatibility and deformation coordination between the developed sensor and asphalt concrete. Therefore, the results of this study provide a new idea for accurate, long-term, and stable acquisition of dynamic response of pavement.