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Abstract
Fibre Bragg grating (FBG)-based optical fire sensors have found numerous applications in various industries over nearly 20 years. The aim of this thesis is to address the technology gap identified through the exploration and development of a series of FBG-based sensors for structural health monitoring and required by industry. The primary objective of the work is to explore the use of polymer-coated FBGs as sensors in the cementious matrix to monitor moisture which is considered as a main agent involved in most of the chemical attacks, by transporting corrosive ions in concrete structures. The sensing concept used in this work exploits the inherent characteristics of the FBG and is based on the strain effect induced in the FBG through the swelling of the polymer coating. A direct indication of the moisture level is given by the shift of the Bragg wavelength caused by the expansion of the sensing material. The context of the work, both technical and applications-focuses and the development and characterisation of the sensors are discussed extensively in this thesis. The effectiveness of the sensors developed was evaluated through a series of tests performed under various harsh conditions using a range of concrete specimens with different porosity and mix composition, designed in collaboration with civil engineers. Results of the work are reported and relevant conclusions drawn for the use of this technology in the civil engineering sector, as well as incorporating a discussion of future trends and potential wider applications.