Fig .4. Effect of fiber content on the compressive strength of geopolymer (a) little; and (b) much[42]. Reproduced from [42], with permission from [Publisher]
In short, the strong bond between geopolymer and fiber may be related to the following aspects: (a) different reaction mechanism and reaction products of geopolymer and cement-based materials; (b) strong adhesion of N-A-S-H to matrix; (c) the formation of an improved interface transition zone (ITZ) in the geopolymer, which is partially attributed to the fact that cement-based materials tend to form low strength silicates at the ITZ, and partially that the fiber matrix interface is affected by higher pH values.

4.2 Flexural strength

Considering the brittleness caused by the internal structure of geopolymer cross-linked each other, adding fiber can significantly enhance the flexural properties of geopolymer, while considering the crack bridging mechanism of fibers, the bending strength of fiber reinforced geopolymer is significantly higher than that of unreinforced geopolymer.