*3.5. Water Absorption*

The results of the water absorption test are illustrated in Figure 11. With more fiber additions, the water absorption of geopolymer concrete increased. For geopolymer concrete, the nylon66 fibers with a 2.0% concentration have the maximum water absorption (0.057). This is because the workability reduced with the addition of nylon66 fibers as discovered in this study, which might cause an increase in the creation of pores.

**Figure 11.** Water absorption of geopolymer concrete with addition of plastic fibers.

Permeability is a measure of how efficiently water, air, and other chemicals, such as chloride ions, can be absorbed by geopolymer concrete. Similar to OPC concrete, geopolymer concrete also contains pores that enable the absorption of particular compounds. Higher porosity leads to higher water absorption, which lowers the density of the concrete. Meanwhile, less porosity leads to a higher density of geopolymers, decreasing water absorption. Figure 11 shows the significant relation between water absorption and density, as well as how fiber addition appears to improve water absorption due to higher density. The weak interfacial interaction of Nylon66 fiber with the matrix could lead to the formation of a void, which would increase water absorption as fiber addition increased. Furthermore, as the amount of nylon66 fiber in geopolymer concrete increases, the degree of compaction in the mix decreases, encouraging the volume of air voids in the geopolymer concrete.

According to Jawad et al. [11], when using nylon fibers, water absorption is increased by 3–6%. As compared to samples of ordinary concrete, samples of concrete reinforced with nylon fibers absorb slightly more water. Improved connection between microchannels in the concrete's outer surface and binder matrix may be to blame for this. Additionally, studies show that the addition of fibers improves concrete captivity and water absorption due to the lengthening of the microchannels in the microstructure.

This degradation would affect the performance of the geopolymer concrete's fiber reinforcement, including its compressive strength, flexural properties, fiber matrix interfacial bonding, and durability against blasting. It is essential that geopolymer concrete

has minimal water absorption for better performance. The geopolymer concrete samples obtained from this study have a high potential for corrosion resistance due to low water absorption and the use of fiber material. Water absorption was investigated by weighing the sample after it was removed from the water, since in NRGPC, it alters the qualities of fibers made with poor resistance to corrosion. Because nylon66 fiber has a low water absorption rate and is unaffected by corrosion, the amount of fiber used in this investigation was not measured.

#### *3.6. Slump Test*

Using a standard slump cone, the slump was measured. In this study, the geopolymer concrete's consistency and workability were assessed using the slump test. Figure 12 shows the decrease trend of workability for geopolymer concrete with addition of nylon66 fiber.

**Figure 12.** Slump of geopolymer concrete with addition of plastic fibers.

Figure 12 shows that the slump test result for geopolymer concrete without the inclusion of nylon66 fibers was 100.101 mm. The slump of geopolymer concrete with nylon66 fiber addition reduced with increasing additions of nylon66 fibers from 0% to 2%, which are 95.87 mm (0.5%), 86.3 mm (1%), 80.3 mm (1.5%), and 65.5 mm (2.0%). This has demonstrated that the presence of nylon66 fibers makes geopolymer concrete less workable. This finding suggests that the 65.5 to 100 mm range has low and medium workability.

This outcome also proved that the presence and addition of fibers significantly negatively impacted the workability of geopolymer concrete. This is due to increased friction between the geopolymer concrete matrix and fibers. The addition of more fibers causes the viscosity of new geopolymer concrete to increase because more binder is absorbed by the fibers' higher surface area, resulting in low slump.

In addition, the fiber and coarse aggregate particles were noted to have compatible dimensions, which contribute to resisting the relative mobility of the latter. The flow of fresh geopolymer concrete was resisted in this condition, making it more difficult for coarse particles to move. This interlocking of fiber and aggregate is depicted in Figure 4. As a result, the difficulty of the relative movement between the coarse aggregates and the movement of the mixture increases with the number of fibers added. The mixture flows much more slowly and becomes less workable. The slump test was carried out using a slump cone and a mixture of fresh NFRGC, measuring the distance between the surface of the latter and the top of the slump to gauge the combination's workability.
