Recent Advances in the Use of Green Corrosion Inhibitors to Prevent Chloride-Induced Corrosion in Reinforced Concrete

Abstract

Inhibitors for the prevention of corrosion in reinforced concrete are chemical substances able to reduce carbon steel reinforcements corrosion without altering the overall properties of concrete. Today, many commercially available substances have a negative impact on human safety during either the inhibitor synthesis, their handling or application in field. Green corrosion inhibitors are nontoxic, biodegradable and environmentally biocompatible substances. They are generally made of extracts from natural plants or waste, which are abundantly available in several countries. The majority of green inhibitor molecules usually contain multiple bonds, aromatic rings, polar functional groups and electronegative atoms as P, N, S or O; the latter are able to coordinate with metal cations to form protective layers on the metallic surface of the reinforcements, so as to inhibit the development (initiation and/or propagation) of the corrosion process. In this review, the most recent achievements on the study and investigation of green corrosion inhibitors for concrete structures are presented and discussed. Inhibitors are classified based on their nature and inhibition mechanism. The inhibition effectiveness of the substances is compared with the well-established effective nitrite-based inhibitor, distinguishing between accelerated and long-term tests. Based on the available data, a summary of corrosion inhibitors efficiency is reported.

Keywords: bacteria; chloride-induced corrosion; concrete; green inhibitors; plant extracts; rebars corrosion; waste materials.

Figure 1

Electrochemical equivalent circuits used to fit EIS spectra after (a,b) exposure to Cl⁻ without and with inhibitor (c,d) (reprinted with permission from [35]).

Figure 2

Pictorial representation of the GIM inhibition mechanism on low-carbon steel in 1 M NaOH + 1 M NaCl solution (reprinted with permission from [41]).

Figure 3

Guar gum extract chemical composition (reprinted with permission from [51]).

Figure 4

i_corr as a function of chloride ion concentration calculated through linear polarization. A SCP solution blank system; B1 3 wt.% extract 1#; B2 3 wt.% extract 2#; B3 3 wt.% extract 3#; B4−, B4, B4+, respectively 1, 3 and 5 wt.% extract 4#; C 3 wt.% DMEA; D 1 wt.% sodium nitrite (reprinted with permission from [60]).