Monitoring of concrete at very early age using stiff SOFO sensor

The SOFO system is based on low-coherence interferometry in single-mode fibres and allows the measurement of deformations in civil structures built with classical civil engineering materials (concrete, steel and wood). It has been successfully tested in different types of structures such as bridges, dams, tunnels and piles. In order to monitor behaviour of concrete at the very early age a stiff SOFO sensor has been developed. Using standard SOFO sensor it is possible to measure deformation of concrete at the very early age (thermal swelling and shrinkage). However, by coupling it with a stiff sensor, it is possible to determine the hardening time of concrete and to measure initial stress in the rebars. The stiff sensor and the results obtained using its first prototype are presented in this paper.