Fig. 12. Mechanism of fiber resistance to SO42- and Cl-[26]
Reproduced from [26], with permission from [Publisher]
In short, fiber-reinforced composites matter considerably in combating against the harsh conditions of the ocean. The bridging effect of randomly distributed fibers inhibits the initiation, development and penetration of cracks in the matrix, delays the diffusion of SO42- and Cl- into the base, and prevents against physical (freeze-thaw process) and chemical (SO42- and Cl- erosion) attacks[63], which also resists the fatigue load of sulfate crystallization and optimizes the pore structure[73, 76, 77]. When the local geopolymer is subjected to loading pressure, fibers weakly bonded to the matrix will break first, form microcracks and produce elastic deformation afterwards. The mass loss of terpolymer sulfate erosion leads to the formation of porous structure and sulfate crystal phase, thereby resulting in strength loss[26].

5.3 Freezing-thaw resistance

The freeze-thaw cycle is one of significant indexes to evaluate the durability of the geopolymer[78]. In geopolymer structures, water mainly exists in three forms, i.e., crystal water, gel water and free water. Crystal water and gel water will not be frozen because of its small pore, while only the free water with capillary pores will freeze at a negative temperature. The resistance against geopolymer can be effectively improved by reducing the porosity and improving the compactness of the structure[12].