The use of corrosion inhibitors is one of the promising protection methods for controlling steel corrosion in concrete because of their low cost and easy application. The development and application of surfactant corrosion inhibitors have drawn special attention. Many surfactants have inviting application prospects for the corrosion protection of metals. Cetyltrimethylammonium bromide (CTMAB), a cationic surface active agent, has been studied for metal corrosion protection due to its main advantages of non-toxicity and a popular price. Nevertheless, there is little information on CTMAB as a corrosion inhibitor for steel in concrete.
In this work, the surfactant CTMAB was employed as a corrosion inhibitor and its inhibition performance against reinforcing steel corrosion in the simulated concrete pore solutions was studied by electrochemical measurements and surface analyses.
The cylindrical specimens with Ø11.2 mm × 4 mm were cut from a Q235 reinforcing steel bar. The specimen mounted in epoxy resin was used as the working electrode with an exposed area of 1.00 cm2during electrochemical measurements, and a platinum sheet and a saturated calomel electrode (SEC) served as the auxiliary electrode and the reference electrode, respectively. The compositions of the specimens were analyzed by X-ray energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and their morphologies were observed by scanning electron microscopy (SEM).
A saturated Ca(OH)2 solution with pH about 12.50 was selected as a simulated concrete pore solution. After the solution was adjusted to pH 11.00 with a 0.8 mol/L NaHCO3solution and 0.5 M NaCl was added, it served as a simulated polluted concrete pore (SPCP) solution, namely a test solution. Then different concentrations of CTMAB were added to the SPCP solution to investigate the corrosion inhibition effect of CTMAB on the reinforcing steel.
The EIS analysis of the steel in the SPCP solution showed the capacitive reactance arc size increased gradually while the CTMAB concentration was increased from 0 to 0.005 M, then decreased with the increasing of the CTMAB concentration from 0.005 to 0.1 M. When the CTMAB concentration was 0.005 M, the interfacial charge transfer resistance (Rct) of the steel reached a maximum of 41.17 kΩ cm2, and the inhibition efficiency of CTMAB was 79.9%.
The inhibition efficiency of CTMAB determined from the polarization curve of the steel in the SPCP solution with 0.005 M CTMAB reached 87.6%, indicating that the CTMAB could inhibit corrosion of reinforcing steel effectively. For the SPCP solution without CTMAB there was not a passive region on the potentiodynamic anodic polarization curve of the steel, indicating that the steel corrosion took place. However, the steel was in a passive state for the solution with 0.005 M CTMAB. The SEM results also indicated that CTMAB could protect the steel from corrosion.
XPS and Raman results proved that CTMAB was an adsorption type corrosion inhibitor. The adsorbed CTMAB resulted in the formation of a protective film on the steel surface to protect the steel from corrosion.