Fig. 2. The interfacial bonding of different fibers with geopolymer
steel fiber[31]; (b) glass fiber[14]; (c) basalt fiber[14]; (d) polypropylene fiber[31]; (e) jute fiber[23]; (f) sisal fiber[23][14, 23, 31]
Reproduced from [14, 23, 31], with permission from [Publisher]
Fig. 2(a) shows that the steel fiber and geopolymer matrix contact well, and there is no interface peeling phenomenon. Given that steel fibers are often hydrophilic, they can significantly improve the energy absorption and bending strength of composites[31]. The glass fiber and basalt fiber in Figures 2(b) and 2 (c) present obvious interfacial debonding with geopolymer. The addition of glass fiber increases the compressive strength and flexural strength of the matrix by 32.6 % and 30.35 %, respectively, while the addition of basalt fiber increases the compressive strength and flexural strength of the matrix by 27.3 % and 35.36 %, respectively[14]. Fig. 2(d) describes the interface bonding between polypropylene fiber and geopolymer matrix. Organic fiber also shows the interface peeling phenomenon, and the addition of adding polypropylene fiber increases the compressive strength and flexural strength of the matrix by 27.5 % and 16.07 %, respectively. Fig. 2(e) (f) depicts the interfacial bonding between jute, sisal fiber and geopolymer in natural fibers. The jute with a mass fraction of 1.5 % increases the compressive strength and tensile strength of the matrix by 64 % and 45 %, respectively, while the sisal fiber with a mass fraction of 2.5 % increases the compressive strength and tensile strength of the matrix by 76 % and 112 %, respectively.
The bonding between steel fiber and geopolymer is found the best, and no interface peeling phenomenon is observed. Considering the high strength and rough surface of steel fiber, the mechanical bonding force with geopolymer is formed, and leads to the optimal mechanical properties of geopolymer.