Effect of Primer Layer and Curing Method on Geopolymer Paste Coating Properties

This technical paper presents a comprehensive study on the properties of geopolymer coating applied to mild steel pipelines as a potential alternative to Ordinary Portland cement (OPC) concrete structures. The geopolymer paste was formulated using a mixture of fly ash and alkaline activators, specifically sodium hydroxide (NaOH) solution and sodium silicate (Na2SiO3) solution. Two types of primers, epoxy metal primer and self-etch primer were applied before the geopolymer coating and various curing conditions were investigated. The geopolymer samples were subjected to two different curing processes: one set was cured in an oven at 60°C for 24 hours while the other set was left to cure under ambient conditions. After the curing period, the samples were aged at ambient conditions for 28 days. The properties of the fly ash and geopolymer paste were evaluated through a range of tests including phase analysis, morphology analysis, optical emission spectroscopy (OES) analysis, chemical composition analysis and adhesion strength testing. The results revealed that the geopolymer coatings exhibited surface cracks and efflorescence attributed to unreacted sodium oxide. X-Ray diffraction (XRD) analysis confirmed the presence of quartz, hematite, magnetite, aluminum oxide and mullite in the geopolymer coating. The self-etch primer-coated samples demonstrated improved adhesion and corrosion resistance properties with a denser and more cohesive microstructure. The geopolymer coating when applied with a self-etch primer and cured at 60°C for 2 hours, achieved the highest adhesion strength of 2.2 MPa, indicating strong bonding with the mild steel pipelines. These findings contribute to the understanding of geopolymer coatings and their potential application in enhancing the performance and durability of mild steel pipelines, offering a sustainable alternative to conventional concrete coatings with improved corrosion resistance and adhesion properties.