Studi Kuat Tekan Beton Terhadap Substitusi Semen Dengan menggunakan Ground Granulated Blast Furnace Slag (GGBFS) K-300

Concrete is the primary construction material whose usage continues to grow, yet the production of cement as its main binding agent contributes significantly to high CO₂ emissions. Therefore, innovations using eco-friendly partial cement replacements, such as Ground Granulated Blast Furnace Slag (GGBFS), are essential. This study aims to analyze the effect of partially replacing cement with GGBFS on the slump value of fresh concrete and the compressive strength of K-300 grade concrete. The substitution percentages of GGBFS utilized were 0% (normal concrete), 10%, and 20% by weight of cement. Compressive strength testing was conducted on cubic specimens measuring 15x15x15 cm at testing ages of 7 and 28 days using the water curing method. The test results demonstrated that adding GGBFS slightly reduced the slump value from 11 cm in normal concrete to 10 cm in the 10% and 20% GGBFS variations; however, these values still satisfied good workability criteria. For compressive strength, GGBFS substitution exerted a significant positive effect. At 28 days, concrete compressive strength consistently increased with higher GGBFS content, where equivalent cylinder strength f'c rose from 21.45 MPa to 24.42 MPa, reaching a maximum of 28.39 MPa at 20% GGBFS (representing increases of 13.86% and 32.35% for the 10% and 20% variations compared to control concrete) due to additional Calcium Silicate Hydrate C-S-H gel formation densifying the concrete microstructure. Consequently, replacing cement with up to 20% GGBFS is effective for K-300 grade concrete to enhance mechanical performance while advancing sustainable green concrete technology today.