**2. Materials and Methods**

#### *Preparation of NFRGC*

In this study, Nylon66 Fiber Reinforcement Geopolymer Concrete (NFRGC) was used in the formation of geopolymers alongside other materials, including fly ash, alkali activator, and aggregates. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) were combined to create an alkali activator with a ratio of 2.5. 12M of NaOH concentration was used in this research, which was achieved by diluting the NaOH pellet in distilled water at the desired concentration. Meanwhile, the ratio of fly ash to an alkali activator was fixed at 2.0. All of the selected ratios for the formation of fly ash geopolymers in Tables 1 and 2 were based on the previous findings [13].

**Table 1.** Mix design of nylon66 fiber reinforced geopolymer concrete for compressive.


**Table 2.** Mix design of nylon66 fiber reinforced geopolymer concrete for flexural.


The fly ash class C used in this study was taken from the plant Manjung, Perak, Malaysia. There are two types of aggregates used in this study: fine and coarse. River sand was used as fine aggregate, and granite was used as coarse aggregate, with sizes of 4.7 mm and 20 mm, respectively. The combination ratio for both aggregates is 60% coarse and 40% fine by weight. Meanwhile, the ratio between geopolymers and aggregate is 40% geopolymers and 60% aggregate.

Fly ash and alkali activators are mixed at a ratio of 2.0 to create the geopolymer paste. Nylon66 fibers of diamond form were used in this experiment, which involved Interlocking Chain Plastic Beads (ICPB). The volume fraction of samples with compressive and flexural strengths of 0%, 0.5%, 1.0%, 1.5%, and 2.0% was used to determine the amount of nylon66 fibers to add to the geopolymer concrete mixture. Addition of 0%, 0.5%, 1.0%, 1.5%, and 2.0% by volume were tested for compressive strength testing. Additional information on Nylon fiber specification used in the production of NFRGC is summarized in Figure 1.

**Figure 1.** The plastic fiber and specification.

To create the required and precise shape and dimensions of the plastic bead, a unique mold was created. The beads' shape was created using the plastic injection molding process. With controlled speed and pressure, a molten nylon66 resin mixture colored with white was injected into the mold. The substance was then freed from the mold after cooling and taking on the appropriate form. The procedure was repeated in order to obtain more units. Six (6) different beads per set make up the linked plastic beads. They had two and three-bead systems cut off. This study does not include a fiber-type processing step. The fiber type was applied in this study to investigate the effect of ICPB in geopolymer concrete, since studies on the diamond shape of ICPB are still limited. Nylon66 is noted as a polymer, and thus has poor bonding between matrix and fiber compared to metallic fibers, but excellent corrosion resistance. In this study, new virgin material was used instead of recycled material to reduce impurities.

There is no standard shape for aggregates because they all have unique forms; however, spherical and angular aggregates are the most popular and function well. Additionally, as aggregate shapes are inherently uneven after crushing and display similarities in terms of shape, size, and surface roughness, it is impossible to design or manufacture something that is precisely like an aggregate. Based on the situation, diamond-shaped beads were chosen as the form for the beads. The diamond shape is both round and slightly angular.

The NFRGC samples were cast in (100 mm × 100 mm × 100 mm) and (500 mm × 100 mm × 100 mm) molds for physical (workability, density, and water absorption) and mechanical (compressive and flexural) testing. Following a 24 h curing period, samples were removed from the mold and allowed to cure for 28 and 90 days at room temperature.

A slump test was used to evaluate the NFRGC's workability. The ASTM C143 guidelines were followed for performing the slump test. After mixing, three layers of newly created geopolymer concrete were poured into a slump cone. Twenty-five tamping rod strokes were used to compress each layer. From the cone's top, fresher NFRGC was scraped off. The freshly constructed NFRGC was then immediately raised vertically to eliminate the concrete cone's workability. The slump was calculated by determining the separation between the top of the slump cone and the original center, which had been shifted, of the top surface of the new NFRGC.

A density test was conducted on the 28-day sample. A sample was submerged in water at room temperature for 24 h. In a water tank, the NFRGC sample was positioned apart from one another without touching. The top of the sample surface was no more than 150 mm relative to the still water line. To guarantee there was a 3 mm space between the sample and the bottom of the water container, the immersed sample was set on a wire mesh.

The 24 h immersed sample of NFRGC was weighed and recorded (Wi). The sample was then taken out of the water tank and left to dry for one minute. A moist towel was used to remove any apparent water from the sample's surface. Afterwards, the sample was weighed and recorded as being saturated (Ws). After that, the sample was dried for 24 h at 110 ◦C in an oven. Following that, the dried sample was weighed and given a dried weight label (Wd).

A Universal Testing Machine (UTM) Automatic Max was used to determine the compressive strength of sample NFRGC in accordance with standard BS 1881-116. (Instron, 5569, Norwood, MA, USA). This testing was done on samples that were cured for 28 and 90 days at room temperature. A load speed adjustment of 0.1 kN/s was made.

The flexural test was carried out to gauge the sample's flexural strength. Using the UTM model Automatic Max, the sample was put through a 4-point bending test (Instron, 5569, Norwood, MA, USA). The testing was carried out according to ASTM C1018. This study used a constant deflection rate that ranged from 0.05 to 0.10 mm/min. The lower and top supports were 300 mm and 100 mm in height, respectively. After being cured at room temperature for 28 and 90 days, the sample was examined.

#### **3. Results and Discussion**

#### *3.1. Chemical Composition*

Table 3 provides a summary of the chemical composition of the fly ash used to make geopolymer concrete with both types of fibers. There are five major elements that contribute to the properties of geopolymers, comprising SiO2, CaO, Fe2O3, Al2O3 and MgO. It is worth noting that fly ash is composed of silicon oxide, aluminum oxide, iron oxides, and other minor oxides. Major components including SiO2 and Al2O3 contribute almost 90% of the total weight of fly ash. Meanwhile, Fe2O3 content is less than 5% of the total weight of fly ash. From Table 3, the total composition of SiO2 and Al2O3 are 43.9%, followed by CaO with 22.30%, Fe2O3 with 22.99%, and MgO with less than 1%. According to the chemical composition obtained, the fly ash used in this study was classified as Class C fly ash [14]. In addition, the fly ash used meets the basic requirements for a source of material to be used as a precursor due to its high Si and Al content, which is significant for creating geopolymer bonds.

**Table 3.** Chemical composition of fly ash.


Si-O-Al appeared as one of the most significant linkages that affected the strength of the geopolymer, and the combination of Si and Al maps demonstrated how it formed. The geopolymer typically has a favorable setting time due to being high in calcium (Ca) content. Although there was a significant difference in the amount of Ca in the two geopolymers, it was discovered that the strength growth was gradual. Meanwhile, increasing curing temperature and time resulted in increased strength. The presence of Si and Al components in geopolymer composites influences strength development because more geopolymer chains are formed, which strengthens the geopolymer composite materials. The majority of the geopolymer's basic structure is made up of Si-O-Al, demonstrating the importance of Si and Al components in producing strong development. The presence of Mg, however,

slowed the geopolymer's strength growth. This has disrupted the Ca-Si-O-backbone Al structure, reducing the geopolymer's ability to produce strength. In addition, due to the development of hydrotalcite group phases and a decrease in the amount of readily available Al element, appropriate Ca enables the formation of low Al C-(A)-S-H.
