Measurement of early age deformations in cement-based materials using distributed fiber optic sensors

This paper presents an innovative approach to embedded deformation measurement in cement-based matrices using distributed fiber optic sensors (DFOS). The first 24 h after casting is a complex and dynamic process that has a significant impact on the subsequent quality, performance and durability of the material. Traditional deformation measurement techniques have limitations, particularly in terms of spatial resolution, variation or interruption of the hydration process. In this study, the suitability of Rayleigh scattering based DFOS for the detection of early deformation in mortars was evaluated. Experiments were performed at standardized prisms according to EN 196, using both uncoated (UCF) and ORMOCER® coated fibers (OCF). The measurements were performed under controlled environmental conditions with full temperature and humidity compensation. The results show a high reproducibility with low variation of the measured values at different samples. A negative deformation was observed after the first two hours. This was followed by expansion, which may be related to ettringite formation, thermal expansion, reabsorption of bleeding water and hydration discussed in the literature. These observations are in agreement with recent hydration models which assume a fundamentally expansive hydration process. The study demonstrates the suitability of DFOS technology for accurate and reliable measurements of early deformation in cement matrices. The continuous monitoring of concrete components over their entire life cycle opens up new possibilities for the optimization of concrete structures and contributes to a better understanding of the complex early deformations, including cracking or the influence of reinforcement.