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Nano silica additive:
Micro silica is one of the materials that in current decades used in concrete and attracted the attention of building engineers. Due to typical pozzolanic properties of micro silica, its usage to improve mechanical properties and durability of concrete has increased in advanced countries.it usage in concrete had a lot of advantages included: decreasing of fractures due to cement hydration , better durability against sulfate damages and acidic waters and attaining to final high resistance using types of concrete super plasticizers. other usage advantages of micro silica is decreasing of chlorine ions mobility and then decreasing of penetration depth of chlorine in concrete ,especially in southern coastal areas of Iran. its usage items are included concreting related to construction of marine docks, piles, columns and precast joints, automation foundation and all of concrete structures that are in impose of chemical attacks, specially chlorine ion and sulphates.
In current years, studies are concentrated on silica nanoparticles, it aims to use this material to increase concrete properties. Addition of Nano silica to concrete increases the pressure, tensile and flexibility resistance and decreases setting time and water permeability and increases resistance against chemical attacks. The conducted experiments on nano silica show that not only, these particles aren’t problematic for environment, but provide the better results in comparison with micro silica. Researches have showed that adding of nano silica more than micro silica increases the concrete resistance .Combination of nano silica with concrete in long term preserves health of workers, concrete and environment. Nano silica can decrease the cement usage, improves the concrete quality and increases efficacy.
Addition of 10% nano silica increases pressure resistance of concrete up to 26%, while same amount of micro silica increases resistance of concrete up to 15%. Even with addition of 0.25 % nano silica, we can increase the pressure resistance of concrete up to 10% and increase flexibility resistance up to 25%.
Sio2 Nano is a super advanced additive and it is based on nano technology that has designed to attain to specific concretes .usage of nano silica in concreting nearby the sea coasts has attracted attention of civil engineers .According to unique characteristics of nano silica such as improvement of mechanical properties and increasing of concrete durability, it’s using process has increased in advanced countries. Non-crystalline nano with very fine particles and nano diameter is suitable to use as a cementitious substance in concrete.
Usage and application of sio2 nano is according to ASTMC1240 standard.
Concreting in sea coasts, docks and bridges
Construction of high resistance concretes
Construction of concrete of docks, channels, tunnels, water reservoirs and sources
Flooring and landscaping
Construction concretes which are exposure to corrosion
With addition of nano silica to concrete mix, active sio2 combined with free calcium hydroxide Ca(OH)2 in the concrete capillary pores and produced insoluble calcium silicate crystal and finally condensed cement paste structure and decrease permeability and increase concrete resistance .The advantages of this substance included increasing of pressure, flexibility and tensile resistance of concrete, increasing of concrete resistance against erosion, noticeable permeability decrease of concrete, avoidance from chlorine and sulfate ions penetration and other destructive chemical materials into concrete.
Amount of consumption:
Exact amount of sio2 nano consumption is determined by workshop tests. Hence as a guidance, it is recommended that sio2 nano can add with 3% to 7% ratio of cement to concrete weight (it can replaced with cement because it increases concrete resistance).since nano silica can reduce water, it should use with Dezo super plasticizers. Otherwise, it fractures the concrete and reduced efficacy and rise to non- condensation of concrete.
When constructing the concrete , combine necessary amount of Sio2 Nano with dried components and then add water and super plasticizer.