Seiring dengan perkembangan teknologi dibidang rekaya struktur di Indonesia, penggunaan beton masih banyak digunakan seperti pekerjaan pembangunan gedung, bendungan, jalan.Pada penelitian ini pembuatan beton menggunakan limbah steel slag sebagai bahan pengganti agregat kasar dan fly ash baja sebagai subsitusi semen.Bahan tambahan ini bertujuan untuk Mengetahui pengaruh penambahan steel slag sebanyak 0%, 25%, 50%, 75% dari jumlah agregat kasar dan fly ash sebanyak 10 % dari jumlah semen terhadap kuat tekan beton dan Absorpsi. Pengujian kuat tekan beton dilakukan pada umur beton 7 hari, 14 hari dan 28 hari sedangkan absorpsi dilakukan pengujian setiap umur beton 28 hari. Dari penelitian diperoleh kuat tekan beton yang tertinggi terdapat pada beton variasi 4 ( fly ash baja 10% + steel slag 75%) sebesar 28,686 MPa, sedangkan hasil pengujian absorpsi tertinggi terdapat pada beton variasi 4 ( fly ash baja 10% + steel slag 75 %) 1,860. Nilai slump tertinggi diperoleh dari beton tanpa steel slag dan slump terkecil diperoleh beton variasi 4 ( fly ash baja 10% + steel slag 75%)

Along with developments in the field of structural engineering technology in Indonesia, the use of concrete is still widely used in construction works such as high rise buildings, roads, dams etc. concrete is easy to work on and can be shaped as desired. In this study the manufacture of concrete using steel slag waste as a substitute for coarse aggregate and steel fly ash as a cement substitution. This additional material aims to determine the effect of adding steel slag as much as 0%, 25%, 50%, 75% of the amount of coarse aggregate and fly ash as much as 10% of the amount of cement to the compressive strength of concrete. Concrete compressive strength testing is performed at the age of concrete 7 days, 14 days and 28 days while absorption is tested every 28 days. From the research, the highest concrete compressive strength was found in concrete variation 4 (steel fly ash 10% + steel slag 75%) of 28,686 MPa, while the highest absorption test results were in concrete variation 4 (steel fly ash 10% + steel slag 75% ) 1,860. The highest slump value obtained from concrete without steel slag and the smallest slump obtained concrete variation 4 (10% steel fly ash + 75% steel slag)