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 the material hydration. A fluorescent molecular probe, Naphth-AlkyneOMe is en-trapped in a cross-linked polyvinyl alcohol-glutaraldehyde matrix to synthesize thin films with pKa values increasing with glutaraldehyde ratio. The obtained sensing films with an average thickness of 150µm show reversible responses to pH change. 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.