# Development and Evaluation of Nano-Silica Sustainable Concrete
###### Abstract
In the early stage, the early strength improvement effect of nano-silica concrete was more obvious due to the more sufficient pozzolanic reaction [10]. As the curing time increased, the particle size decreased, which weakened the pozzolan response of nano-silica. Therefore, the improvement effect of nano-silica on concrete strength in the later period was reduced [10]. [PERSON] et al. [11] conducted a study about the effects of nano-silica addition on the workability of Portland cement pastes. The nano-silica slurry used in this experiment consisted of 10.2 PH, 30 silica content (wt%), 0.56 itrable alkalis (wt% as Na2O), 1.22 Density (g/cm\({}^{3}\)), 5.5 viscosity (mPa s), 10 mean particle size (nm), and 345 specific surface area (m\({}^{2}\)/g). The workability of fourteen mixtures with different water/binder ratio and nano-silica concentrations in the liquid phase were evaluated using mini-slump tests. The addition of nano-silica to cementitious mixes produced a remarkable reduction of the mix workability, due to instantaneous interactions between the nano-silica sol and the liquid phase of the cementitious mixes (mainly dissolved alkalis), with the formation of gels characterized by high water retention capacities [11]. The delayed addition of mixing water aliquots proved to be an effective way of reducing the adverse effect of nano-silica on mix workability, without changing the water/binder ratio and/or adding superplasticizer [11]. However, the delayed water addition did not improve the workability of the Portland cement mixes. Moreover, due to the reduction of the nano-silica reactivity caused by the instantaneous interaction between superplasticizer and nano-silica, the immediate superplasticizer addition was considered to be useless in improving the workability of the mixtures. On the contrary, delayed addition of the superplasticizer, coupled with the use of an appropriate mixer for the break-down of the gels formed from nano-silica sol destabilization, proved to be the best procedure to uniformly disperse the mix ingredients, without significantly penalizing the nano-silica reactivity [11]. [PERSON] et al. [12] investigated the beneficial role of nano-silica in cement-based materials. The nano-silica in the concrete acted as a nucleation site to accelerate the hydration of cement and also filled the pores to give higher packing density, which led to higher strength with lesser porosity [12]. The development of nano-silica based high-performance concrete will help in decreasing the consumption of cement for specific grades, which will help in protecting the environment to a great extent. Furthermore, due to the high compressive strength, the nano-silica based high-performance concrete will produce smaller structural members, which will reduce the total amount of materials placed and consequently reduce the overall cost of the structure. Moreover, the high early strength development of nano-silica based high-performance concrete will accelerate the construction process, which will save time, money, and materials. Finally, the long service life of the nano-silica based high-performance concrete will reduce the maintenance costs to a great extent. [PERSON] et al. [13] studied the effect of the particle size of nano-silica on the compressive strength and the optimum replacement content of cement mortar containing nano-silica. Three different particle sizes of nano-silica (12, 20, and 40 nm) were used in this experiment. Two groups of mixtures were tested, in which the first group incorporated different dosages of silica-fume, and it consisted of four mixtures, and the second group incorporated different dosages of nano-silica, and it consisted of four mixtures. Compared to the silica-fume mixtures, the compressive strength of the nano-silica mixtures was greater due to the pozzolanic activity and the packing ability. The mixture that incorporated 40 nm nano-silica showed the highest compressive strength compared to the mixtures with 12 and 20 nm nano-silica.