Synthesis of fly ash/metakaolin geopolymer for concrete retrofitting application

The purpose of this research is to use fly ash as raw material to synthesize geopolymer paste that can replace traditional epoxy resin for concrete reinforcement purpose. Fly ash and metakaolin are mixed with alkali solution at predetermined SiO2/Na2O modulus to form geopolymer pastes, which were then used as a binding agent between carbon fiber reinforced polymer (CFRP) and the concrete substrate. According to the test results, the geopolymer paste synthesized with 0.75 SiO2/Na2O modulus alkali activator have the highest mechanical strength and fire resistance. Under ambient condition, the compressive strength of the concrete cylinder bonded to one layer and two layers CFRP using geopolymers binder is 1.5 times and 2 times of original concrete cylinder, respectively. Under 85% compressive strength loading and elevated temperature, the CFRP (geopolymer) bonded concrete cylinder failed at 516 °C. These test results proved that geopolymer can be a potential binding material for concrete rehabilitation due to its high‐mechanical strength and excellent fire resistance.