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Due to the increasing use of concrete and the use of additives in it , research in this direction is very important . Resistance is one of the effective values in the design and control of concrete quality that numerous factors and parameters affect it . Perhaps increasing in concrete mixing time is one of the parameters that are considered less attention and in this research ; the effect of mixing time on compressive strength of Nano - silica concrete with pozzolan rice husk was studied and were compared with concrete without Nano - silica and pozzolan rice husk .Therefore the effect of sulfate to reduce the resistance of this type of concrete was studied and compared . So , a number of pieces of concrete cube with sides of 15 cm contains %1 Nano - silica and 20% pozzolan husk Rice with a time of mixing varies between 10 to 40 minutes , that every 5 minutes , 3 samples of concrete were taken and made in the days 3 , 7 and 28 under the stress test and ultimately the results of mixing different compressive strength by the time was drawn and reported . Rice husk also tested and its components determined and compared with the standard . Nano - silica concrete and concrete pozzolan rice husk and without Nano – silica and pozzolan was also photographed to compare the density of particles , and at the end testing plan was written by Taguchi testing of concrete . The results show that for the most compressive strength of concrete pozzolan Nano comes with rice husk , the right time (optimal) 25 minutes with a Taguchi test results differ by about 9 percent lower than the margin of error is permitted , that at this time the concrete maximum compressive strength shows the maximum compressive strength at 28 days after the concrete 415 kg/cm2 and then does not show significant strength concrete . Pozzolan concrete without silica and rice husk increasing mixing time increases the compressive strength of concrete 375 kg/cm2 in 28 days from the time the concrete mixing process increase the resistance of shows . Ash consumption in the non - crystalline silica , which is 88% of the project , has shown its high pozzolanic activity . Physical and chemical (XRF) examination showed that rice husk ash used in this project within the requirements of ASTM C-618 for pozzolan is located . XRD results show that the consumer is fully amorphous silica from rice husk ash . As the electro - microscopic pictures (sem) is observed in samples without Nano - silica and pozzolan rice husk , the concrete has uneven texture and large crystals are clearly visible which are connected with needle - shaped crystals and large pores are clear in concrete . However , the concrete samples with Nano - silica and rice husk pozzolan , concrete has a more amorphous structure which are homogeneous and integrated together . And the porosity of the concrete is significantly reduced , which increases the resistance of concrete.

Keywords: Nano-silica, rice hull pozzolan, mixing time, the compressive strength of concrete, Taguchi experimental design

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