Long term study of passive corrosion of steel rebars in Portland mortar in context of nuclear waste disposal

An experimental campaign was carried out to study the passivity of steel embedded in Ordinary Portland mortar. Mockup samples made of steel coupons (roughly polished or pre-corroded) embedded in mortar were tested under a relative humidity of 80, 90 and 95% or in a solution simulating the ground water of the French site of Bure (at 25 and 50°C) and under aerated and de-aerated conditions, during up to 3 years. The results of gravimetric measurements show that the average corrosion rates determined on polished coupons are typical of passive conditions (<1 μm/year) and vary from 0·2 to 2·3 μm/year for pre-corroded coupons. Moreover, characterisation (Raman spectroscopy and SEM-EDS) of the samples tested in aerated conditions points out a stable state in term of the nature of the corrosion products and of the composition of the steel/mortar interface. In de-aerated conditions, magnetite is observed in the corrosion products.