Multifaceted geopolymer coating: Material development, characterization and study of long term anti-corrosive properties

Abstract Geopolymers are traditionally used as construction and building material to partially replace Portland cement consumption. The versatile properties of geopolymer present it for use as a multifunctional material and geopolymer cementitious coating is an emerging part of it. In attempts to develop green and sustainable geopolymer coating material for advanced application, we studied geopolymeric coating of varying Na/Si ratio and alkaline molarities and their long term corrosion resistant properties on mild steel to protect it from surface corrosion. Chemical characterization was performed using combination of powerful characterization tools, more specifically mineralogical assessment by X-ray diffractometer, bonding arrangements by Fourier transform infrared spectroscopy and microstructural details by Field emission scanning electron microscopy techniques. Time of flight secondary ion mass spectroscopy was also used as novel characterization approach to envision the coating-substrate interface and for elemental mapping at the interface which delivered useful information about occurrence of strong covalent bonds between Si–O–Fe in the form of Fe2OSi+ mass fragment with m/z ratio 156. The material was further investigated in terms of adhesion strength and water/salt resistant, following accelerated salt fog test by ASTM codes. Geopolymer with varying Na/Si ratio and alkaline molarity exhibited change in XRD amorphicity and microstructure. Results also displayed that even at low Na/Si ratio geopolymeric coating performs high adhesion with iron with no considerable change in corrosion resistant properties. The maximum adhesion of developed material with mild steel was 14.68 M Pa. after 28 day ambient curing which presented its functional suitability. Coating sustained point load upto 5 kgs and showed adequate water and salt resistance upto 3 months. In accelerated corrosion environment, optimized geopolymer coating displayed adequate corrosion resistance and displayed rust rating 9. Overall we obtained an optimized material which is well suited for coating of buried mild steel pipes to replace contemporary cement mortar coating in terms of properties, durability, cost effectiveness and environmental sustainability.