Effect of Geopolymer Coating on Mild Steel

Abstract

This paper presents the results of a study on the effect of geopolymer coating on mild steel. Geopolymer is synthesis of a fly ash and alkaline activators which are sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3). Fly ash is one of residue produced during the combustion of coal in coal power plant. In this study, fly ash class F based geopolymer was used as a source material. The alkaline activators then were mixed with fly ash to produce the geopolymer paste which acts as a coating material. The mixture was placed in molds and reinforcement bar were embedded in geopolymer paste. After that, the corrosion behavior of reinforcement bars for all samples were observed by using Open Circuit Potential (OCP) testing. Referring the pourbaix diagram regarding OCP testing, samples are in passivity region. Besides that, mild steel also were coated with geopolymer paste for adhesion test. Elcometer 108 was used for adhesion strength test. Morphology analysis also been used to determine the microstructure of fly ash and geopolymer paste. Phase analysis was used for the analysis phase between fly ash, geopolymer paste and mild steel coated with geopolymer paste. From OCP test, pourbaix diagram shows that samples is placed in the passivity region, iron (III) oxide (Fe2O3) which is in stable phase and iron (II, III) oxide same results as in phase analysis. The minimum potential value for OCP is 0.015 V and the maximum potential value is 0.133 V. For adhesion strength, day 14 got the highest results compared day 7 and day 3 which the results are 2.0 Mpa, 1.9 Mpa and 1.5 Mpa respectively. It is because from day 3 until day 14, the structure of geopolymer paste becomes more compact, denser and better crystallization as shown in morphological analysis.