Effect of Benzotriazole as Corrosion Inhibitor for Reinforcing Steel in Cement Mortar

Abstract

The effects of benzotriazole (BTA) on the corrosion behavior of reinforcing steel in mortar specimens were studied by corrosion potential (Ecorr), polarization resistance (Rp), and resistivity of mortar cover (ρc). Additionally, the corrosion inhibiting efficiencies of BTA and NaNO2 (SN) were compared after exposure to 3.5% (w) NaCl solution for 360 d. Three samples with different surface conditions (as-received reinforcing steel, pre-rusted reinforcing steel, and chloride-admixed in mortar) were studied using electrochemical impendence spectroscopy (EIS), cyclic polarization (CP) and cyclic voltammetry (CV). Environmental scanning electron microscopy (ESEM) and energy dispersive spectroscopy (EDS) were employed to obtain the mechanism of the inhibiting efficiency of BTA in cementitious materials. The results show that under all three conditions, BTA strongly reduces the uniform corrosion rates of reinforcing steels in mortar with inhibiting efficiencies better than those of SN. On the other hand, the pitting corrosion resistance of specimen with BTA is slightly lower than that with SN for the as-received and pre-rusted reinforcing steels. However, when chlorides were pre-mixed in mortar, BTA showed better protection against pitting corrosion. In previous investigations, BTA was found to form a complex film on the surface of the reinforcing steel which restrained the depassivation of the passive film by Cl-. The results of ESEM/ EDS indicate that BTA facilitates more Ca-rich C-S-H gel in the mortar matrix, which may refine the microstructure of the reinforcing steel/mortar interface. The compact microstructure delays the transport of Cl- towards the steel surface, which protects the reinforcing steel effectively. The long-term (360 d) strength of the mortar specimen is not affected obviously when BTA is used in appropriate proportions. © Editorial office of Acta Physico-Chimica Sinica.