A STUDY OF THE EFFECT OF CHLORIDE AND SULPHATE IONS IN CONCRETE SOLUTION ON GALVANIC STEEL CORROSION

• Main Author: Hidayatul Azhar, Aidil
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/47177
• Institution: Institut Teknologi Bandung

Coastal infrastructure development has a big challenge with the presence of aggressive chloride ions in seawater. The steel frame in the concrete will be corroded by sea water which will also damage the building structure. The use of galvanized steel is one of the most cost-effective and easy solutions. The zinc coating on galvanized steel provides protection against corrosion. Apart from chloride ions, one of the other aggressive ions is the sulfate ions. Sulfate ions come from SO2 gas which then carries into the air and forms sulphate salts which will be carried down with the rain. Therefore, it is necessary to study how the influence of these two aggressive ions on galvanized steel in concrete. A series of experiments were carried out to study the effect of NaCl and Na2SO4 in concrete solutions. In this experiment three tests were conducted, namely surface characterization test, immersion test and electrochemical characteristics test. The sample used was galvanized steel with a zinc layer of 0.3mm in thickness. The solution used was a combination of a solution of Ca(OH)2 with a pH of 12 added with salt NaCl and Na2SO4, so that seven combinations of test solutions was formed. Initially all samples were immersed for 10 days with Ca(OH)2 then on the 11th day salts were dissolved in accordance with a predetermined scheme. After that, the desired test was then carried out. The results of the three tests determined the corrosion rate analysis, polarization resistance, tafel extrapolation, surface morphology, and the electrical circuit model that occurs in the corrosion process. In solutions containing one type of salt, higher concentrations indicate lower polarization resistance and higher corrosion rates compared to lower concentrations. In salt mixture solutions, higher Na2SO4 concentrations indicate increased polarization resistance and decreased corrosion rate. In the results of the Scanning Electron Microscope (SEM) test, samples that are immersed in a solution of Ca(OH)2 have passive layer deposited on its surface. In samples that are added with salt, the passive layer looks damaged and pits are formed. The Xray Diffraction (XRD) results of all samples tested indicated that there is an intermetallic compound (Fe13Zn126) on the sample surface. In the sample immersed in a solution added with NaCl salt, there are simonkolleite (Zn5Cl2(OH)8.H2O) compounds detected. The presence of corrosion products deposited on the surface of the sample in the NaCl test solution in the form of a compound simonkolleite (Zn5Cl2 (OH)8.H2O) causes a lower corrosion rate than Na2SO4 at the same concentration. The electrical circuit model suitable for samples immersed in a test solution combined with salt is Rs (CPE1/Rpor) (CPE2/Rf) (CPEdl/Rct). This model shows that the passive layer formed from Ca(OH)2 solution is damaged by chloride ions and sulfate ions to form pits.