Fly Ash is a waste material from coal burning at thermal power plant. Power Plant Sijantang produces ± 600 tons per day and it is an environmental problem in the area. In this study, the waste fly ash substituted into concrete K-225 or fc'=19.04 MPa amounted to 0%, 5%, 10%, 15%, 20%, 25% and 30%. Results optimum compressive strength at 5% substitution. After that the additive is added Sikamen NN 0.3%, 1.3% and 2.3%.The addition of 2.3% additive produces compressive strength of 298.59 kg / cm2 very much required at 225 kg / cm2. On the addition of additive 0.3% age 28 day compressive strength of 279.19 kg / cm2, the larger the required amount of 225 kg / cm2. Without the addition of additive, compressive strength of 218.35 kg / cm2, less than the required amount of 225 kg / cm2. So for concrete K-225, mix with the substitution of 5% and 0.3% addition of additives can be used as a standardmixture.