ABSTRAKJauhnya lokasi batching plant dengan tempat penuangan kerapkali membuat beton setting sehingga dibutuhkan bahan tambah retarder. Ground Granulated Blast Furnace Slag (GGBFS) memiliki komposisi kimia mirip semen. Oleh karena itu, dilakukan penelitian penambahan retarder pada beton dengan substitusi GGBFS sebagai pengganti sebagian semen untuk mengetahui pengaruh (dengan uji regresi SPSS),  sifat  fisik  dan  mekanik  beton,  serta  mendapatkan kadar  optimum penambahan retarder. Metode penelitian ini menggunakan metode eksperimental dengan variasi campuran 90% semen, 10% GGBFS dengan retarder 0%, 0,2%, 0,4%, dan 0,6% berat semen dengan fas 0,5 sesuai SNI 03-2834-2000. Hasil penelitian menunjukkan retarder 0,2% - 0,6% mampu meningkatkan kuat tekan sebesar 19,61 - 50,59%. Berdasarkan hasil penelitian diperoleh kadar optimum 0,2% karena memiliki sifat paling baik.Kata kunci: GGBFS, kuat tekan, retarder ABSTRACTLong distance between batching plant to the pouring area often causes the concrete undergo a setting, so that a retarder addition material is needed. Ground Granulated Blast Furnace Slag (GGBFS) which has a chemical composition similar to cement. Therefore, a research was conducted on retarder addition to concrete with GGBFS substitution as a partial cement substitute to obtain the effect (regression analysis method in SPSS), physical and mechanical properties of concrete, and to obtain the optimum level of retarder addition. This research used an experimental method with a mixture variation of 90% cement, 10% GGBFS with retarder percentage as follows; 0%, 0.2%, 0.4%, and 0.6% of cement weight with a water/cement is 0.5 according to SNI 03-2834-2000. The results of research with the addition of a retarder of 0.2% - 0.6% were able to increase the compressive strength by 19.61 - 50.59%. Based on the results, the optimum level of retarder is at a variation of 0.2% as it has the best physical and mechanical properties.Keywords: GGBFS, compressive strength, retarder