Effect of Inhibitors on the Bond Strength of Rebar an‎d Geopolymer

10/18/2025 12:00:00 AM

The production of ordinary Portlan‎d cement (OPC), as one of the most widely used construction materials, has led to a considerable increase in greenhouse gas emissions an‎d environmental pollution. Consequently, geopolymers have emerged as a promising alternative binder. A geopolymer is an inorganic material formed through the reaction of aluminosilicate precursors with an alkaline activator. By eliminating cement, it can reduce CO₂ emissions by up to 80% an‎d, when properly formulated, improve the durability an‎d mechanical properties of concrete—including the bond strength between steel reinforcement an‎d the matrix. The bond between rebar an‎d geopolymer is of particular importance in this replacement, an‎d previous studies have reported improvements compared with Ordinary Concrete. However, corrosion of reinforcing steel remains a major factor that weakens this bond, while the influence of corrosion inhibitors on bond performance has received limited experimental attention. Therefore, the present study investigates the effect of tartaric acid, used as a corrosion inhibitor, on the bond behavior between steel reinforcement an‎d geopolymer paste. For this purpose, geopolymer pastes based on metakaolin an‎d pumice were synthesized using sodium hydroxide an‎d sodium silicate as activators at different concentrations an‎d mass ratios. Based on the compressive an‎d flexural strength results, the optimal parameters for both pastes were determined as 10 M NaOH concentration, Na₂SiO₃/NaOH ratio of 2.5, an‎d solution-to-binder ratio of 0.75. After optimizing the curing conditions, the fresh mixed specimens were cured at 80 °C. afterwards, tartaric acid was added into the geopolymer mixtures at three dosages of 0.01, 0.03, an‎d 0.05 wt% of the binder, which increased the fluidity by approximately 35%. In Metakaolin pastes, adding tartaric acid to the geopolymer at levels of 0.01, 0.03, an‎d 0.05 wt% caused an increase of 2.6, 3.2, an‎d a decrease of 13.1%, respectively, an‎d in pumice pastes, it caused a decrease of 34.7, 17.2, an‎d 18%, respectively, in the compressive strength at age of 7 days. In terms of flexural strength, tartaric acid addition caused 32%, 29%, an‎d 43% reductions in metakaolin-based mixtures, while the pumice-based pastes showed decreases of 11.7% an‎d increases of 0.8% an‎d 19.9% at the respective dosages, compared to the control samples. Finally, bond strength (pull-out) tests revealed that tartaric acid significantly enhanced the bond performance of both geopolymer systems at 3 an‎d 7 days. In metakaolin-based geopolymers, the bond strength at 7 days increased by 186.5%, 194.6%, an‎d 175.6% at 0.01, 0.03, an‎d 0.05 wt%, respectively. Similarly, the pumice-based mixtures exhibited bond strength improvements of 92.8%, 97.6%, an‎d 57.1% under the same conditions. This enhancement is attributed to the formation of hydrogen bonds, Chelation of alkaline ions, reduced Kinetics of geopolymerization reaction, an‎d a denser gel structure—especially in the interfacial transition zone around the rebar. Microstructural analyses confirmed these mechanisms.

ژئوپليمر , متاكائولن , پوميس , مهاركننده , تارتاريك اسيد , پيوستگي

Geopolymer , Metakaolin , Pumice , Inhibitor , Tartaric acid , Bond strength

Moein Shirdel

Asghar Habibnejad Korayem