Attachment and Visual Observation of a Photonic Crystal-Based Mechanochromic Sensor on Concrete, Masonry, and Timber Components: A Preliminary Experimental Evaluation

Crack monitoring in building components requires sensing methods that accommodate different surface conditions while maintaining consistent observation conditions. This preliminary study investigated a photonic crystal-based mechanochromic sensor for visual crack monitoring of concrete, masonry, and timber components. Attachment and observation characteristics were examined considering surface conditions and crack behavior. In the concrete T girder, the sensor tended to change from blue toward green hues as cracking progressed and detached at the shear failure stage. For masonry, the attachment location and method were selected considering surface irregularities between bricks and mortar joints, and crack development was observed with a crack gauge installed near the sensor. For timber, irregular crack paths and difficulties in direct attachment were observed, and a clamping frame was applied to restrain displacement and rotation of the sensor. A measurement device was developed to maintain the relative positions of the sensor, camera, and light source during repeated imaging. Based on these observations, attachment and image-acquisition procedures were proposed for repeated visual crack monitoring. Initial remote image-acquisition functions were implemented, and an integrated architecture incorporating Long-Term Evolution (LTE) and an independent power supply was proposed to support future expansion to practical applications.