Fig .3. Effect of fiber content on the compressive strength of
geopolymer
[12-14, 18, 21, 23, 28, 33-41].
The effect of different fiber contents on 28 d compressive strength of
geopolymer is listed in Fig. 3.
Due to the high rigidity of steel fibers, its addition improves the
compressive strength of geopolymer. The experimental results of Zada
Farhan show that 6mm steel fibers improve the compressive strength more
efficiently than 12mm steel fibers[34], and that the alumina coating
can improve the interfacial bonding strength between steel fiber and
geopolymer, which is 151% higher than that of uncoated steel
fiber[3]. With the increase of polypropylene fiber content, the
decrease in strength is attributed to the formation of interpolymer
voids and weak interfacial bonding zone. Murthy’s study shows that 1%
is the best content for polypropylene fiber to improve the compressive
strength of geopolymer[35], while Bellum’s research indicates that
2% is the best content for polypropylene fiber to improve the
compressive strength of geopolymer[13], and Wang’s study considers
0.8% polyvinyl alcohol fiber the best dosage to improve the compressive
strength of geopolymer. However, Wang and Li’s study indicates that a
higher polypropylene fiber content represents a higher compressive
strength[18] [37]. Xu has found that the optimal dosage of
basalt fiber to improve the compressive strength of geopolymer is 0.6%,
and that the comprehensive performance of 6mm basalt fiber is better
than that of 3mm basalt fiber [38]. Wang’s study shows that a higher
content of basalt fiber indicates a better compressive strength[14],
and Bai’s study recognizes 0.4% glass fiber as the best dosage to
improve the compressive strength of geopolymer. Glass fiber can
eliminate the microcrack of polymer and improve the mechanical
properties of geopolymer[28]. Silva’s research shows that a higher
sisal fiber content means a better compressive strength[23].
Wongsa’s study implies that sisal fibers greater than 0.5% reduces the
compressive strength of geopolymers[21], that the jute fiber optimal
dosage is 0.5%, and that the cotton fiber optimal dosage is
0.5%[41]. More than 0.5% of coconut fiber decreases the
compressive strength of the geopolymer[21].
As shown in Fig.4, internal tensile stress is generated when the fiber
reinforced geopolymer is squeezed by external force. The appropriate
amount of fiber can play a bridging role and effectively inhibit the
crack propagation. The strength growth percentage of cement-based
materials caused by fiber inclusions is usually lower than that of
geopolymer, which can be explained by the ceramic-like and polymer-like
properties of geopolymers and better fiber matrix interface. Geopolymer
has finer pore distribution than cement-based materials.