# Development and Evaluation of Nano-Silica Sustainable Concrete
###### Abstract
On the other hand, water sorptivity was determined by using (100 \(\times\) 500 mm) cylindrical slices. Along with the other tests used in this experiment, the researchers were able to come up with multiple conclusions. First, nano-silica showed a clear pozzolanic reaction with the Portland cement. This reaction, along with the nanofiller effect of nano-silica, made the microstructure of the concrete more homogeneous and less porous. Consequently, the permeability was reduced, which increased the compressive strength and the resistance of the concrete against water penetration and chemical attacks such as chloride ions. [PERSON] et al. [5] investigated the use of nano-silica to improve mechanical and fractural properties of a fiber-reinforced high-volume fly as cement mortar. The materials used in this study were nano-silica, OPC type 1 42.5 N, fly ash class F, PVA fibers, and river sand. Four series (16 mixes) of experiments were carried out to evaluate the effect of nano-silica (NS) on the fractural and mechanical properties of polyvinyl alcohol fiber-reinforced high-volume fly ash mortars (PVA/HVFAM), with the fly ash/binder ratio fixed at 50 wt%, NS/binder ratios of 0-1.5 wt%, and PVA fiber dosages of 0-1.0 vol% [5]. After conducting the tests, multiple conclusions were drawn. First, the incorporation of 0.5-1.5 wt% nano-silica improved the compressive strength, tensile strength, elastic modulus, fracture energy, fracture toughness, brittleness index, and critical tip opening displacement compared to plain high-volume fly ash mortars (HVFAM). Second, compared to plain HVFAM, the incorporation of 0.2-1.0 vol% PVA fibers had no pronounced effect on the elastic modulus and compressive strength. However, it improved the tensile strength, fracture energy, fracture toughness, brittleness index, and critical tip opening displacement. Third, the synergetic effect of NS and PVA was observed, in terms of the post-peak behavior under static bending as well as the fracture parameters [5]. Finally, the microstructure analysis, which was performed using the scanning electron microscopy, showed that additional C-S-H was formed and covered the surface of the PVA fibers due to the accelerated hydration process that occurred due to the high reactivity of NS. This improved the bond between the PVA fibers and the cement-based matrix and resulted in an efficient load-transfer by fiber bridging [5]. [PERSON] et al. [6] conducted a study about the effect of nano-silica on the strength and durability of fly ash-based geopolymer mortar. Fly ash-based geopolymer mortar has a shortcoming, which is the need for heat activator to develop early strength. To overcome this, the researchers developed an experiment of using low calcium fly ash geopolymer with different molar concentrations of activator liquid and different nano-silica percentage dosages. The addition of 6% of nano-silica to the fly ash-based geopolymer mortar showed an obvious increase in compressive, flexural, and tensile strength at 28 days under ambient temperature curing. Furthermore, the same percentage of nano-silica reduced water absorption. The modification that took place in the geopolymer with 6% of nano-silica is due to the transformation of the amorphous compound to the crystalline compound. [PERSON] et al. [7] investigated the properties of concrete incorporating nano-silica. Two types of concrete were investigated in this experiment, which are concrete with ordinary cement and concrete with ordinary cement plus class F fly ash. To link macro and micro-scale trends and study the effect of using nano-silica, the research included tests of adiabatic temperature, rapid chloride ion permeability, mercury intrusion porosimetry, thermogravimetry, and backscattered scanning electron microscopy. Based on the test results, multiple conclusions were reached. Both types of concrete used in this experiment showed a remarkable improvement in performance due to the addition of nano-silica. The nano-silica was responsible for accelerating the kinetics of hydration reactions.