The UPM team used weldable fiber optic sensors based on FBG (Fiber Bragg Grating) instead of more traditional methods, such as infrared thermography, acoustic emission, digital image correlation (DIC), ultrasonic sensors, plastic optical fibers or carbon nanotube sensors.
As the sensors can be welded to the rebar, it was possible to measure the strains of a structure from within, not only of the concrete but also of the steel itself,
said Julián García Díaz, doctoral student in Technological Innovation in Building.
Fiber optic sensors were chosen because of their characteristics, and in particular, their longevity compared to conventional electric strain gauges, long-term signal stability in unfavourable conditions, the option to place several sensors on the same cable (multiplexing) and immunity from interference (EMI/RFI). Furthermore, the cable length does not affect the measurement process. All this translates into cost advantages and improvements in performance and accuracy.