Bridge expansion joint device with color-changing sensor

Expansion joint device with stress-chromic polymer coating on finger plates and concrete blocks for visual deformation monitoring

This technology is a bridge expansion joint device consisting of a pair of concrete blocks placed facing each other across a joint gap, an expansion joint that changes width based on block movement, and a color-changing sensor coated on the surfaces to indicate deformation.

Expansion joints absorb bridge deck deformation caused by loads, temperature fluctuations, and concrete shrinkage or creep. Traditionally, fiber Bragg grating sensors were used to detect deformation by measuring changes in light properties. However, this required multiple fiber-optic and strain sensors at every joint, leading to complex structures and high installation costs.

This technology features an expansion joint composed of support brackets on the blocks, a V-shaped gutter, interlocking finger plates, and a buffer between the plates and blocks. A stress-sensitive polydiacetylene-based polymer sensor is applied across the boundaries of these components, changing color when displacement occurs. The sensor is created by polymerizing diisocyanate, amino-terminated polydimethylsiloxane, and diacetylene via UV or heat. Applicable to highway bridge joints, urban elevated railways, and long-span bridges, it allows for visual inspection of joint behavior directly from the road surface without fiber-optic wiring or instrumentation, enabling proactive maintenance.

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Key Features:

• A pair of concrete blocks placed facing each other across a joint gap on the bridge deck
• A pair of finger plates with interlocking grooves and protrusions, placed on support brackets atop the concrete blocks
• A buffer provided between the finger plates and concrete blocks, with its top surface coated with a color-changing sensor along with the concrete block surface
• A stress-sensitive polymer color-changing sensor coated on at least one surface of the concrete blocks or the expansion joint to change color under stress

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This invention was developed with support from the Ministry of Science and ICT for the development of a durability evaluation platform for stress visualization and quantification based on stimuli-responsive polymer composites.

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