New Optical Sensors for Determination of Corrosion in Reinforcement Concrete

Corrosion of reinforcement steel of concrete is one of the main causes of deteriorations of structures. Principally, it is an electrochemical process, which can be divided by two mechanisms - acidic and chloride initiated corrosion. Optical sensoric materials were prepared, which allow a non-destructive monitoring of these processes. The sensors are embedded into concrete structures and the signal is transported through optical fibres. pH-indicator azo dyes have been synthesised for monitoring of acidic attack. An aldehyde group has been used as dye-reactive functionality for the first time. The dyes have been covalent bound to poly(vinyl alcohol co ethylen) by acetal spacer bridge to assure long-term stability of the sensor. The colour change of such prepared pH-indicator materials occurs in the pH interval of 11 to 13 and allows to predict the acidic attack in an early stage. The response time of these sensors is in the range of seconds. The optical detection of chloride ions in alkaline media has been investigated. Benzimidazolotrimethine dyes tend to form J-aggregates under influence of chloride ion concentration in pH of 10 to 13. A suitable polymer has been developed - poly(vinyl alcohol co vinyl butyral), in which the dye is dissolved as host-guest system. Such prepared sensor material allows a precise determination of chloride concentration and shows an excellent selectivity against other anions, which are typical in the presence of concrete structures. To the best of our knowledge it is the first optical sensors for determination of chloride in alkaline media.