Investigation of passive layer formation on steel rebars in foamed concrete

Foamed concrete is a versatile lightweight material which is increasingly being considered for structural and semi structural applications. This would inevitably involve incorporation of steel reinforcement inside foamed concrete. The presence of large volume of air voids in the vicinity of steel could unfavorably affect its electrochemical behavior and jeopardize the formation of the passive layer. In the current study the passive layer formation of steel embedded in foam concrete with 55% air content was investigated and compared to that of steel embedded in the same mix without foam incorporation, that is, the base mix. The electrochemical tests included half-cell potential, linear polarization resistance (LPR), potentiodynamic test, and electrochemical impedance spectroscopy (EIS). The results of half-cell potential and the LPR test show that a passive layer forms within 3 weeks of casting steel inside foamed concrete which is similar to that observed for the steel in the base mix. The results of the potentiodynamic and the EIS tests which were carried out at the age of 28 days confirmed the passivity of reinforcement embedded in both foamed concrete and the base mix