Practical use of distributed fibre optic sensors in research on FRCM composites

This article describes research on FRCM (Fabric Reinforced Cementitious Matrix) composites, which unlike commonly used FRP (Fibre Reinforced Polymers) composites make use of a mineral matrix instead of epoxy resin, which allows to achieve much higher resistance to elevated temperatures. In the described studies, experimental measurement of deformations with the use of the DFOS (Distributed Fibre Optic Sensors) method was applied. This method allows for geometrically continuous measurement of deformations, which is its significant advantage compared to traditional electric resistance wire strain gauge, as it reduces the possibility of measuring deformations in a place where they are not representative. The tests were carried out using two reinforced concrete slab elements loaded to failure in the 4-point bending scheme. Fibre optic sensors were installed on an unstrengthened control element and on an element strengthened with FRCM composite. During the tests, deformations of the concrete under tension and the external surface of the FRCM reinforcing composite were determined. Measurements were carried out simultaneously in two manners: using the DFOS method, and strain gauges placed at the characteristic points of the element. The test results based on both methods were compared and analysed. The comparative analysis confirmed the usefulness and effectiveness of the DFOS method while measuring deformations in strengthening composites, and showed its significant advantages such as precise indication of the place of elements cracking as well as the possibility of conducting a global analysis of deformations.