Fluoride induced corrosion of steel rebars in contact with alkaline solutions, cement slurry and concrete mortars

Corrosion behaviour of mild steel rebars has been studied in contact with 0.01 N NaOH. saturated lime water. cement Slurry and embedded mortars having different concentrations of fluoride ions. Weight-loss, electrochemical DC cyclic polarisation and polarisation resistance, surface topographic and X-ray diffraction (XRD) techniques hake been used to investigate the effects of fluoride ion on the corrosion behaviour of the material. Under all the conditions of the exposure it is observed that it low content of fluoride ( less than or equal to 25 ppm) in the corrodent has deleterious action on the performance of the steel, where as Lit its higher content ( greater than or equal to 100 ppm) the ion has rather an inhibiting effect on corrosion rate. XRD studies of the corrosion product accumulated on the steel surface in the presence of fluoride ion indicate the predominance of magnetite oxide phase. Accelerating effect of the ion is observed to be due to depolarisation of cathodic reaction of the corrosion process, Observations show that in accelerating range kf fluoride ( less than or equal to 25 ppm) it has almost double corrosive effect than noted for equal concentration of chloride ion. (C) 2002 Elsevier Science Ltd. All rights reserved.