Fluorescent molecular probe based optical fiber sensor dedicated to pH measurement of concrete

An optical fiber sensor based on a fluorescent molecular probe has been developed to measure the pH of cementitious materials, from the early stages of hydration to advanced ageing of the material. A fluorescent molecular probe, Naphth-AlkyneOMe was entrapped in a cross-linked polyvinyl alcohol-glutaraldehyde matrix to generate thin films with well-defined physicochemical and photophysical properties. The obtained sensing films, with an average thickness of 150 mu m, have showed reversible and reliable responses to pH changes. The developed optode has the required characteristics for the study of concrete, with a response time of 100 s and a precision of +/- 0.1 pH units. Measurements of pH were performed on the surface of low-pH cement paste samples after 4, 6, 7 and 8 days of hydration.