Development and Field Construction Protection of a Fiber Bragg Grating-Geogrid Integrated System in Asphalt Pavements

Facing the challenges in field monitoring of the mechanical response of geogrids in asphalt pavements, this study integrated two types of Fiber Bragg Grating (FBG) sensors, unarmored and armored, into geogrids using the pillar-stitching technique on industrial warp-knitting production lines. The integrated FBG-geogrid systems were comprehensively evaluated in both wound and flattened configurations, enabling the selection of a sensor type suitable for industrial production. After precise strain calibration, a full-scale field damage test was performed during the construction of the Qu-Gang Expressway in Hebei Province, China. The results demonstrate that the helical steel armor layer significantly enhances the mechanical durability of the FBG sensor. Specifically, the armored sensor maintained stable optical transmission over its entire 60-m length, with an average performance retention rate of 98.86% in the flattened state. Moreover, a strong linear correlation was established between the wavelength shift of the armored FBG sensor and the tensile strain of the geogrids. In contrast, the unarmored FBG sensor underwent irreversible shear deformation during production and contained at least two breakpoints. Additionally, a protection scheme employing fiberglass-reinforced silicone rubber on the hot side and standard silicone rubber on the cold side effectively shielded the sensors from high-temperature and compaction loads during asphalt paving. Consequently, the proposed FBG-geogrid integration method and the corresponding field protection strategy provide technical support for the real-time monitoring of geogrid performance in asphalt pavements and have significant engineering value.