A concept suggests that the increases in flexural or tensile test results must be higher than those in compressive strength when using steel fibers and a specific nanomaterial in a fixed ratio for geopolymer concrete. This concept, known as the "synergistic effect" of combined reinforcement, has been studied in recent literature (Shah et al., 2021; Shen et al., 2020). According to Shah et al. (2021), adding steel fibers and nanomaterials can create a synergistic effect that results in more robust and durable geopolymer concrete. Similarly, Shen et al. (2020) found that using steel fibers and nanosilica in a geopolymer mixture improved flexural and tensile properties compared to a control mixture without these additives. It should be noted, however, that the extent of this synergistic effect may vary depending on the type and proportion of steel fibers and nanomaterials used, as well as the properties of the geopolymer mixture. For instance, a study by Ali Dattatreya (2020) showed that adding a specific type of steel fiber had a more pronounced effect on geopolymer concrete's flexural strength than compressive strength. Meanwhile, the type and dosage of nanomaterial can also affect the degree of improvement in both properties (Zhang et al., 2017). Overall, while the synergistic effect of combined reinforcement in geopolymer concrete has been observed in recent studies, the exact increase in flexural or tensile strength over compressive strength may vary depending on several factors. Further research is needed to determine the optimum combination of steel fibers, nanomaterials, and geopolymer mixtures to achieve the highest increase in both properties.

References:

Ali, M. A., & Dattatreya, J. K. (2020). Mechanical properties of steel fiber reinforced geopolymer concrete: A review. Materials Today: Proceedings, 37, 3069-3073. https://doi.org/10.1016/j.matpr.2020.06.441

Shah, S. P., Doski, H. D., Petrov, K. R., Vaidya, H., & Goltermann, P. (2021). Manufacturing and mechanical properties of steel fiber reinforced engineered geopolymer composites (EGCs): Construction and Building Materials, 284, 122853. https://doi.org/10.1016/j.conbuildmat.2021.122853

Shen, X., Dong, X., Tan, L., & Chen, C. (2020). Effects of steel fibers on fly ash-based geopolymer concrete's mechanical properties and microstructure. Construction and Building Materials, 250, 118921. https://doi.org/10.1016/j.conbuildmat.2020.118921

Zhang, Y., Ke, X., Du, H., Yao, H., & Nie, J. (2017). Mechanical properties of hybrid fiber reinforced engineered geopolymer composites with nano-silica and alkaline activated fly ash. Materials & Design, pp. 131, 455–462. https://doi.org/10.1016/j.matdes.2017.05.014