Optimizing Mounting Techniques for FBG Sensors to Minimize Measurement Errors in Concrete Deformation Tracking

The reliability of fiber-optic Bragg grating (FBG) sensors for monitoring reinforced concrete structures is determined by the efficiency of strain transfer across the sensor-structure interface. However, mounting methods are often chosen empirically, resulting in measurement deviations. This study quantitatively compares two surface mounting methods for FBG sensors: mechanical fastening through a metal substrate and adhesive fastening. The novelty of this study lies in the comprehensive quantitative assessment of the strain transfer coefficient for the two mounting methods using reference strain gauges, temperature compensation, and triplicate experiments. The experiments were conducted on reinforced concrete specimens and with two concrete compositions under step loading from 0 to 10 kN. Mechanical fastening provided a transmission coefficient of k = 0.92 with an error of less than 12%, while for adhesive fastening, k = 0.41 with an error of over 53%. Spectral analysis additionally demonstrated differences in the reflection-peak characteristics of the two investigated FBG sensors; however, these differences were not interpreted as direct evidence of localized structural damage.