Demonstration of a fibre-optic sensing technique for the measurement of moisture absorption in concrete

• Published in: Smart materials and structures 2006-04, Vol.15 (2), p.N40-N45
• Main Authors: Yeo, T L, Eckstein, D, McKinley, B, Boswell, L F, Sun, T, Grattan, K T V
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Measurement and testing methods; Physics; Servo and control equipment; robots; Solid mechanics; Structural and continuum mechanics
• ISSN: 0964-1726; 1361-665X
• DOI: 10.1088/0964-1726/15/2/N03

A fibre-optic-based humidity sensor has been developed and used for the measurement of moisture absorption in concrete. The sensor was fabricated using a fibre Bragg grating (FBG) coated with a moisture sensitive polymer. To investigate the use of this sensing technique for the detection of moisture ingress in concrete, the sensor was embedded in various concrete samples of different water to cement ratios which were then immersed in a water bath. A direct indication of the humidity level within a sample is given by the shift of the Bragg wavelength caused by the expansion of the humidity-sensitive material coated on the fibre. The sensor itself exploits the inherent characteristics of the FBG, with its operation being based on the strain effect induced in the Bragg grating, through the swelling of the polymer coating.