Too much CO2 is released during cement production. In many researches, the use ofnatural or recycled compounds plays an important role in the cement composition.The use of these components contributes both to reducing the amount of waste andto protecting the environment in nature. It is possible to produce an environmentallyfriendly concrete, thanks to its being a fly ash thermal power plant waste and its useas mineral additive in terms of its composition. In this study, it is aimed to produceimpermeable concretes with the use of C type fly ash as substitutes for cement in concrete composition in substitution rates of 10 %, 30 % and 50 %. In order to reduce thepermeability of concrete in this direction, as a result of grinding the fly ash in the ballmill for 0, 10, 20, 30, 45 and 60 minutes, concrete samples were prepared with andwithout admixture (Reference). Capillarity test was performed to determine the permeability at the end of cure periods of 28 and 90 days on concrete samples. Accordingto the results obtained at the end of 28 days, the best impermeability was achieved inthe mixture with 50 % fly ash replacement and 60 minutes grinding time. In 90 days,the best impermeability was obtained in the mixture with 30 % fly ash replacementand 0 minutes of grinding time. As a result, it was seen that permeability decreasedwith increasing thinness and substitution rate of fly ash in concrete composition.