Bond performance of GFRP and steel rebars embedded in metakaolin based geopolymer concrete

Abstract

This research investigates the bond performance of metakaolin based geopolymer concrete (GPC). Pullout tests were conducted for steel and GFRP bars embedded in plain and fiber-reinforced GPC. Three types of mixes were adopted to produce plain and steel fiber-reinforced GPC by controlling both alkaline solids to metakaolin ratio and sodium silicate to sodium hydroxide ratio. Comparative reference tests were also performed on cement concrete. Concrete splitting was observed for plain geopolymer mixes with both GFRP and steel bars. The steel fiber-reinforced GPC having GFRP bars experienced bar pullout while specimens with steel bars failed by concrete splitting, bar pullout, or bar rupture. For cement concrete mixes, the bond strength of steel bars was better than that of GFRP bars. The average normalized bond strength of plain GPC mixes was generally lower than that of cement concrete by 11%–27% and 21%–40% for steel and GFRP bars, respectively. The inclusion of steel fibers in GPC improved the bond performance for specimens with steel and GFRP bars by 7%–45% and 33%–114%, respectively. A model is proposed for the prediction of bond strength of GFRP and steel rebars embedded in plain and fiber-reinforced GPC.