Performance of refractoriness geopolymer with alumina additive for ceramic weld backing applications

Back shielding gases are important for weld root quality in oxidation-sensitive materials. Metallic backing with gas venting is effective but heavy, costly, and limited in geometry and length, whereas ceramic backing is more suitable for controlling root shape than oxidation protection. Geopolymers offer a promising ceramic substitute with high thermal resistance and room-temperature processability. However, conventional MK–FA geopolymers have limited resistance when directly exposed to the intense heat of molten metal, which can be improved by alumina addition. This research focused on develop a thermally resistant and reusable geopolymer-based weld backing by tailoring alkali/pozzolan ratios (0.6–1.0) and incorporating alumina powder (0–15 wt%). Geopolymer specimens were examined in terms of compressive strength, refractoriness, microstructural development, thermal conductivity, and their performance during welding. The 0.6FM80A10 formulation was the best formula, offering the most balanced combination of properties. Its microstructure showed clear signs of densification, maintained phase stability even when exposed to temperatures approaching 1200 °C and lowest thermal conductivity (0.2645 W/m·K). Because of optimum alumina percentage helped tighten the matrix and reduce pore development, thereby strengthening the material and improving its resistance to high temperatures. After using 0.6FM80A10 as backing with venting gases in welding, the results showed that it had adequate heat efficiency, and it remained structurally sound through more than ten welding cycles. This research presented that the geopolymer with alumina additive could serve as sustainable weld backing with gas venting holes as an alternative to commercial metallic backing.