## 1 Introduction  
Class F fly ash, an industrial byproduct of coal fired power stations containing high amounts of silicon and aluminum, has been used in different ways for the production of green cementitious composites and advanced durable geopolymer materials [1; 2]. The production of the fly ash-based geopolymer requires approximately 60% less energy and has at least 80% less CO2 emissions as compared to the manufacturing of ordinary Portland cement (OPC) [3]. Geopolymers are currently being considered as alternative to OPC and have drawn substantial attention for structural applications due to their cost efficiency, chemical stability, corrosion resistance, rapid strength gain at ambient temperature, lower permeability, and superior resistance to fire and acid attacks. Other advantages include good resistance to freeze-thaw cycles as well as excellent remediation of heavy metal ions [4; 5; 6]. Despite being eco-friendly construction material, its large-scale structural application is limited because of quasi-brittle behavior, similar to OPC. To overcome this problem, many researchers have utilized the different types of fibers to reinforce the geopolymer composites [7; 8; 9; 10; 11; 12]. Generally, the addition of different fibers to the geopolymer matrix is proposed to enhance the mechanical properties, such as compressive strength, flexural strength, and toughness. The inherent properties of the fibers, such as aspect ratio and fiber contents, significantly influence the performance of geopolymers. The presence of fibers plays a bridging action in the geopolymer matrixes and controls the crack to propagate, hence increasing its fracture toughness. Fracture toughness is a property of the material to resist cracks when subjected to external loading. Several studies have been performed to measure the fracture parameters of concrete and geopolymers [13; 14; 15; 16]. Therefore, to avoid catastrophic failure of geopolymer structures, the fracture parameters need to be improved. Resistance to fire should be a fundamental characteristic of a geopolymer. The previous studies [17; 18; 19] showed that geopolymer composites had excellent fire resistance when exposed to elevated temperatures. Generally, geopolymers are considered to be resistant, both at high (above 1000 \({}^{\circ}\)C) and low temperatures, due to the freeze-thaw effect. The measurement of freeze-thaw resistance is very important in terms of structural durability. To obtain early greater strengths, nanoparticles, such as SiO\({}_{2}\), are considered as one of the additive materials to cement-based composites. Due to the high reactivity of nano-SiO\({}_{2}\), it accelerates the hydration of cement and behaves as a nucleus for cement pastes. It also acts as nano-filler to dense and improve the microstructure, resulting in reduced porosity of specimens [20]. Nanosilica was also found to be a beneficial additive in improving the microstructure and mechanical properties of the fly ash-based geopolymer, cured at ambient temperature [21; 22]. The effect of nano-SiO\({}_{2}\) on the mechanical strength of geopolymer pastes containing fly ash and ground granulated blast-furnace slag (GGBFS) were investigated at room temperature. The results showed that the microstructure and strength of geopolymers were improved with the addition of nano-SiO\({}_{2}\) (0-3% by weight of fly ash) [23]. The researchers [5] also studied the influence of different concentrations of nano-SiO\({}_{2}\) on the mechanical development of the fly ash-based geopolymer. They concluded that 6% nano-SiO\({}_{2}\), with alkaline activator to fly ash ratio 0.4, gave an appreciable compressive strength under ambient curing. Incorporation of poly vinyl alcohol (PVA) fibers enhanced the compressive and splitting strength of specimens by 9.95% and 61.69%, respectively, as compared to non-fibrous specimens [24].