Initiation and repassivation of pitting corrosion of carbon steel in carbonated concrete pore solution

The initiation, propagation, repassivation of metastable pits of Q345 carbon steel in Cl− containing concrete pore solution were studied by electrochemical noise. The initiation rate of metastable pits increases exponentially up to a constant value with time. After stable pit occurs, the nucleation of metastable pits is mainly induced by the rust layer, and mainly takes place in the outskirt of the rust layer. Stable pits incline to expand horizontally to produce a shallow pit. In addition, high concentration of nitrite can inhibit the nucleation of metastable pits around the rust cover and accelerate the repassivation of stable pits.

Research highlights
► Initiation rate of metastable pits increases exponentially to constant with time.
► Metastable pits can be induced by rust layer and merged with stable pit.
► Stable pit expands preferentially in horizontal orientation on carbon steel.
► Nitrite can inhibit the nucleation of metastable pits and accelerate repassivation.