%K soil, fly ash, geopolymer, UCT, molarity %T PENGARUH PENAMBAHAN GEOPOLIMER BERBAHAN FLY ASH PADA STABILISASI TANAH DASAR TERHADAP ANALISIS NILAI KUAT TEKAN BEBAS (Studi Kasus: Jalan Raya Sobang, Kecamatan Sobang, Pandeglang, Banten) %A Raina Mutiara Aini %L eprintuntirta52306 %D 2025 %X Subgrade soils with low bearing capacity present significant challenges in infrastructure development, as observed at Jalan Raya Sobang, Kabupaten Pandeglang, Banten, which shows a field CBR value of 2,25%. This study aims to evaluate the effect of adding fly ash-based geopolymer on subgrade stabilization, particularly in improving unconfined compressive strength (qu). A series of tests was conducted to analyze the physical properties and qu values. Stabilization was performed by adding 15% fly ash and an alkaline activator solution (NaOH and Na₂SiO₃) with varying NaOH molarities of 8M, 12M, and 15M, and an S/L ratio of 1/2,5. Tests were performed after 0, 7, 14, and 28 days of curing. The native soil was classified as OH (organic clay with medium to high plasticity) with a plasticity index of 18,3%. The addition of fly ash-based geopolymer reduced the PI to 12,2% for B1 (85% soil, 15% FA, 8M NaOH), 8,6% for B2 (85% soil, 15% FA, 12M NaOH), and 7,6% for B3 (85% soil, 15% FA, 15M NaOH). The qu values increased to 15,528 kg/cm² for B1, 18,812 kg/cm² for B2, and 12,46 kg/cm² for B3, with the optimum value observed in B2 after 28 days of curing. %I Fakultas Teknik Universitas Sultan Ageng Tirtayasa