# Development and Evaluation of Nano-Silica Sustainable Concrete
###### Abstract  
In the last decade, nanomaterials made a major breakthrough in the concrete industry by providing the concrete with unique properties. Earlier studies have shown improvement in the early strength of concrete that can accelerate the construction process. In this study, 1% and 2% of nano-silica were added to concrete mixtures that contain 30% and 70% ground granulated blast-furnace slag (GGBS). Adding 1% of nano-silica to the 30% GGBS mixture showed an increase in the compressive strength by 13.5%, 7.8%, 8.1%, and 2.2% at one day, three days, seven days, and twenty-eight days, respectively. The 2% of nano-silica increased the 30% GGBS mixture's compressive strength less effectively by 4.3%, 7.6%, and 4.9% at three days, seven days, and 28 days, respectively, when compared to the 1%. On the other hand, adding 1% and 2% of nano-silica reduced the 70% GGBS mixtures' compressive strength. Moreover, nano-silica reduced the deformability of the mixtures significantly, which caused the increase in the Young's modulus. The flexural strength of the 30% GGBS mixtures had similar behavior as the 28-day compressive strength. On the other hand, the flexural strength of the 70% GGBS mixtures increased as the nano-silica increased. Nano-silica addition improved the microstructure and the interface structure of the mixtures due to its high pozzolanic activity and the nano-filler effect, which is confirmed by RCPT results and SEM images. nano-silica; GGBS; nano-filler effect; pozzolanic activity; nucleation site; agglomeration effect +
Footnote †: journal: Medical  
composition; and (4) NPs improve the microstructure of the interfacial transition zone between aggregates and cement pastes [3]. [PERSON] et al. [3] carried out an experiment studying the hydration characteristic, thermal expansion, and microstructure of cement containing nano-silica. Seven different mixtures were used in this experiment that incorporated nano-silica at different dosages up to 6% partial replacement of OPC. The presence of nano-silica had remarkably increased the water demand, which, in consequence, retarded the setting time. This seemed to be controlled by the particle size distribution and the high specific surface area of NS in the presence of polycarboxylate superplasticizer [3]. Furthermore, the values of pH and free portlandite decreased as the dosage of nano-silica increased. Due to the pozzolanic reaction of nano-silica, the chemically combined water contents increased with increasing nano-silica percentage dosage. The microstructure, and consequently the mechanical properties, of the investigated cement mortars are improved sharply with NS up to 3.0% and then slightly up to 5% [3]. Additionally, using nano-silica as a partial replacement of Portland cement lowered the coefficient of thermal expansion of the hardened cement paste. Moreover, due to the continuous hydration of cement phases and the pozzolanic reaction of nano-silica, the thermal expansion of hydrated cement pastes incorporating 3% nano-silica dosage increased with curing time. The nano-sized SiO\({}_{2}\) up to 5% proved to be an effective mineral addition for blending with OPC to improve its chemical, physico-mechanical, and thermal properties [3]. Finally, incorporating nano-silica increased the compressive strength because of the nano-filler effect, which improved the microstructure and promoted the highly pozzolanic reaction. [PERSON] et al. [4] studied the durability properties of OPC concrete that contains nano-silica at dosages of 0.3% and 0.9%. Three different mix designs were prepared to be tested in this experiment, which are OPC concrete, 0.3 nano-silica concrete, and 0.9 nano-silica concrete. The compressive strength of each mix design was determined at 7, 28, and 91 days by preparing three (100 \(\times\) 200 mm) cylinders for each day, while the water penetration depth was obtained by testing two (100 \(\times\) 200 mm) cylinders at a water pressure of 0.75 MPa for seven days.