ORIGINAL PAPER Corrosion and Fire Protective Behavior of Advanced Phosphatic Geopolymeric Coating on Mild Steel Substrate Pooja Bhardwaj 1 & Rainy Gupta 2 & Deepti Mishra 2 & S. K. Sanghi 2 & Sarika Verma 2 & Sudhir S. Amritphale 2 Received: 23 November 2018 /Accepted: 2 April 2019 # Springer Nature B.V. 2019 Abstract The research objectives of this study were to investigate and compare corrosion and fire protective properties of conventional and advanced phosphatic geopolymeric coating on mild steel substrate using spray coating technique For these studies two compo- sition were developed using conventional geopolymerisation route by adding alkali activator solution to fly ash and six compo- sitions were developed using advanced geopolymerisation process in which water was added to solid precursor powder obtained by together co-ginding of raw materials for a period of 8 h. Coated plates were tested for adhesion strength, water resistance, fire protection and corrosion resistance. Results indicated that coating developed from two passes with thickness 100 ± 15 μm showed better adhesion as compared to single pass and also proved to be promising corrosion protective coating material for mild steel substrate under sea water conditions. The developed material is able to withstand flame for more than 45 min and also no cracks were observed in coating by direct heating on liquefied petroleum gas flame. Thus developed phosphatic geopolymeric material is well suited for protecting the mild steel structures from fire and corrosion. Keywords Advanced geopolymeric coatings . Spray coating . Fire protection . Adhesion strength . Corrosion protection 1 Introduction In the present scenario, with increase in environmental concerns, the significance of geopolymers as coating material is self-evi- dent. Geopolymer coatings are one of the protective coatings which are good in adhesion with substrate, corrosion protection, fire and heat resistant [1–6]. Fly ash based geopolymer are rich in siloxane bond, sialate bond (Al-O-Si) and the metal cations (Na + ) which provide charge neutrality and provides durable coat- ing by utilizing waste of thermal power plant [7, 8] . To increase the protection efficiency of the metal surface from the external environmental conditions, the alkalinity of the geopolymer gel is best suited as it enhances the production of the protective layer over the metal surface [9–11]. The conventional method of prep- aration of geopolymers by sol-gel mechanism is associated with the drawback of handling of hazardous alkali and therefore have limited application spectrum. To overcome the issues associated with conventional technique of geopolymer development a nov- el solid state mechanism of geopolymerization have been con- ceptualized which provide uniform gel matrix and hence im- prove the corrosion resistance behavior of the metal [12].In ad- dition to these properties, the other concerns like strong adhesion and durability of coating on are addressed by adding Ca 3 (PO 4 ) 2 (tricalcium phosphate). Phosphate based coatings are reported to possess effective corrosion protective and fire protective proper- ties, enhance the inhibition efficiency and improve the passivity of the metal surface [13]. Spray coating techniques is most suitable in terms of appli- cability [14] and has been widely used for fabricating the metal substrates for excellent performance and also has broad industrial application. Nowadays, spray techniques is gaining more attention for the recovery of the damaged structural parts [15]. Apart from technique used, adhesion and thickness of coating material were the important parameters in improving the efficiency of the coated-substrate material [16]. In the present studies different compositions of geopolymeric coating material were prepared by conventional as well as ad- vanced technique by varying Na/Si, Si/Al and Ca/Si ratio utilising * Pooja Bhardwaj bhardwajpooja851@gmail.com 1 Academy of Scientific and Innovative Research- AcSIR- AMPRI, Council of Scientific and Industrial Research, Advanced Materials and Processes Research Institute (CSIR-AMPRI), Hoshangabad Road, Bhopal (M.P.) 462064, India 2 Materials for Radiation Shielding and Cement Free Concrete Division, Council of Scientific and Industrial Research, Advanced Materials and Processes Research Institute (CSIR-AMPRI), Hoshangabad Road, Bhopal, MP 462064, India Silicon https://doi.org/10.1007/s12633-019-00153-1