Investigation of interfacial and mechanical properties of alumina-coated steel fiber reinforced geopolymer composites

[Display omitted] •Deflection hardening behavior is more developed in composite containing alumina coated fibers.•Toughness of alumina coated fiber reinforced composite up to δMOR, showed a significant increment of 94% compared with uncoated steel reinforced composite.•Aluminum atoms from the alumina coating can diffuse across the interface and participate in geopolymeric reactions.•Alumina coating on steel fibers results in 151% enhancement in bond strength. In this study, alumina coated steel reinforced geopolymer composites were successfully fabricated and their interfacial and mechanical properties were investigated. The fiber–matrix interface characteristics were assessed using single-fiber push-out and water contact angle experiments as well as SEM-EDS analysis. Finally, the role of alumina coating on the compressive, flexural and toughness of the geopolymer composites was investigated. The morphological studies revealed that alumina coating on steel can chemically bonded and microstructurally integrated with the surrounding matrix. The push-out test showed that the interfacial shear strength was increased approximately 150% in composites produced with alumina coated steel fiber, suggesting an enhancement of stress transfer across the fiber/matrix interface. The results showed that the composites containing alumina coated steel fibers possess significantly higher mechanical properties in comparison with the uncoated specimens under all tested conditions. A comparison of the mechanical properties of composites at 0.75 vol%, showed that the flexural and compressive strength of alumina coated fiber composites were improved by ~ 17% and ~ 14%, respectively. The calculated toughness and load–deflection curves were indicated an improvement up to ~ 94%. It was also found that deflection hardening behavior is more developed in composite containing alumina coated fibers. These results were considered as an effectiveness of alumina coated steel fibers on reinforcing of metakaolin-based geopolymer composites.