Chemische Stabilität von Natriummonofluorphosphat in der Porenlösung des Betons / Chemical stability of sodium monofluorophosphate in the pore solution of concrete

For non-destructive rehabilitation in case of corroding reinforcement the application of sodium monofluorophosphate has been proposed. In practice an aqueous solution of sodium monofluorophosphate is sprayed on the concrete surface.

By capillary suction the inhibitor is supposed to he transported into zones surrounding the corroding reinforcement in order to inhibit further corrosion. Hut the results presented here show that monofluorophosphate decomposes in the alkaline concrete pore solution forming slightly soluble calcium phosphate and calcium fluoride. Calcium phosphate and calcium fluoride are not known to work as corrosion inhibitors. The penetration depth in concrete depends on the properties of the microstructure and the rate of decomposition of sodium inonofluorophosphate. These mechanisms strongly limit the possible concentration near the reinforcement bars and, as a consequence, it is very unlikely to reach the level necessary to maintain the inhibition of corrosion in reinforced concrete.