Bond behavior of deformed steel bars in fly ash–based geopolymer concrete: Test results and development-length implications

Fly ash geopolymer concrete (GPC) is a low-carbon alternative to Portland cement concrete. A reliable bond between steel reinforcement and GPC is essential for structural design. This study investigates the bond behavior of deformed steel bars embedded in fly ash GPC. The GPC mixtures are activated with a sodium hydroxide–sodium silicate solution and heat-cured at 60 °C for 24 h. Pull-out tests are conducted to obtain bond stress–slip curves. The peak bond stress, the slip at peak, and the residual bond stress are reported. The influence of compressive strength and confinement conditions is examined. The test results are compared with common bond models developed for Portland cement concrete. The comparisons show systematic differences in peak bond and post-peak softening. A simple calibration is proposed to adapt existing models for fly ash GPC. The calibrated model is used to discuss development-length implications for reinforced GPC members.