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].