Steel slag is produced from the process of separating the steel liquid heated in a mold of making steel. Steel slag is a solid waste it can be used as an alternative of building construction material. This study aims to analyze the characteristics of the new modified fresh concrete by utilizing steel slag as a coarse aggregate substitution. The variation of coarse aggregate substitution of steel slag was 50% and 100%, and used Chemical Admixture in the form of 0.6% of Plastocrete RT 06 and 3% of Sikament NN of the weight of cement. The compressive strength of the concrete plan was 37,35 Mpa, and used a cylindrical specimen with 7,5 cm in diameter, and 15 cm in height .Soaked the concrete for 7 days, 21 days, and 28 days. From the time set, it was found that the concrete sample of the 50% coarse aggregate substitution variation of steel slag was 120 minutes, 100% steel slag was 105 minutes, and the normal additive concrete variation was slower; thus requiring a binding time of 130 minutes. The test results of normal additive concrete compressive strength within 28 days produced an average value of 23,1 Mpa, concrete variation of 50% and 100% steel slag substitution concrete coarse aggregate were 25,135 Mpa, and 36,745 Mpa, respectively. The test of modified concrete compressive strength was less than the planned compressive strength