Smartec in collaboration with Politecnico of Turin has pervormed a series of crack detection tests in concrete beams using different types of distriuted optical fiber cables.
The test consists of loading the beam in two points until it reaches its ultimate deformation. The beam has a 30 x 15 cm section with 2ø14mm on the upper side and 2ø18mm on the lower side, the length equals 400cm. Smartec installed three distributed strain cables inside the beam (SmartProfileSMARTProfile II and Hydro&Geo) and the other two below the beam (SMARTProfile and SMARTape).
View Paper: “Crack Detection Using Embedded Fiber-Optic Sensors in Reinforced Concrete Beams”.
A DiTest interrogator has been used, with 50cm of spatial resolution and 25cm of sampling interval. All the cables have been joined in a single loop and the reading unit gives a single frequency profile in which different areas represent different types of cable and positions.
Many smaller cracks occurred, between 0.1mm to 2mm. Crack detection with distributed sensors was reliably possible for cracks of 1mm and above, but we are working on techniques to detect smaller cracks.
Three beams have been fabricated and tested for failure. The beams had different reinforcement designs to simulate the formation of single large cracks or multiple smaller cracks.
In the following example, the local strain peak due to crack formation is visible for load step 8.
