Efektivitas Fly Ash dalam Stabilisasi Tanah Ekspansif sebagai Tanah Dasar

Abstract

Tanah ekspansif banyak dijumpai di Indonesia dan menjadi permasalahan pada pekerjaan tanah dasar karena potensi kembang-susut akibat perubahan kadar air dapat mengganggu kestabilan serta menurunkan daya dukung perkerasan. Penelitian ini bertujuan menganalisis efektivitas fly ash kelas C terhadap ekspansivitas, CBR, mikrostruktur, serta menganalisis korelasi fly ash terhadap ekspansivitas dan CBR melalui regresi linear berganda. Pengujian dilakukan pada tanah ekspansif rendah, sedang, dan tinggi dengan penambahan fly ash 5%, 10%, dan 15% melalui curing 7 hari pada kondisi unsoaked dan soaked. Hasil penelitian menunjukkan bahwa penambahan 15% fly ash menurunkan indeks plastisitas sebesar 45,09%, 22,50%, dan 22,06%, serta swelling sebesar 25,86%, 59,09%, dan 64,94% pada tanah ekspansif rendah, sedang, dan tinggi. Seluruh sampel memenuhi batas minimum CBR efektif 6% menurut Bina Marga, dengan peningkatan CBR unsoaked sebesar 3,17 kali lipat, 3,63 kali lipat, dan 3,54 kali lipat, serta CBR soaked sebesar 2,47 kali lipat, 2,67 kali lipat, dan 2,93 kali lipat dibandingkan tanah asli. Analisis SEM dan XRD menunjukkan montmorilonit turun menjadi 0,2%, terbentuk CSH 0,3%, serta struktur tanah lebih padat dan terflokulasi. Analisis regresi menunjukkan korelasi yang kuat antara kadar fly ash, ekspansivitas tanah, dan nilai CBR. Persamaan terbaik diperoleh pada parameter swelling (S = 0,297IP - 0,128FA) dengan R² 0,923, CBR soaked (CBR = 3,581 + 0,260FA - 0,194S) dengan R² 0,962, dan CBR unsoaked (CBR = 5,296 + 0,457FA - 0,143IP) dengan R² 0,858. Hasil analisis regresi tersebut dapat digunakan sebagai acuan awal untuk memperkirakan nilai CBR tanah lempung yang distabilisasi dengan fly ash hingga penggunaan kadar 15%.

Expansive soils are commonly found in Indonesia and pose challenges in subgrade construction because moisture-induced expansion and contraction can compromise stability and reduce the bearing capacity of the subgrade. This study aimed to evaluate the effectiveness of Class C fly ash in reducing soil expansivity and improving CBR performance and investigate microstructural changes, as well as to examine the correlation between fly ash content, expansivity, and CBR using multiple linear regression analysis. Tests were conducted on low-, medium-, and high-expansive soils with 5%, 10%, and 15% fly ash additions, followed by a 7-day curing period under unsoaked and soaked conditions. The results showed that the addition of 15% fly ash reduced the plasticity index by 45.09%, 22.50%, and 22.06%, and the swelling by 25.86%, 59.09%, and 64.94% in low-, medium-, and high-expansive soils, respectively. All samples satisfied the minimum effective CBR requirement of 6% specified by Bina Marga, with unsoaked CBR increasing by 3.17-fold, 3.63-fold, and 3.54-fold, and soaked CBR increasing by 2.47-fold, 2.67-fold, and 2.93-fold compared with the untreated soil. SEM and XRD analyses showed that the montmorillonite content decreased to 0.2%, C-S-H was detected at 0.3%, and the soil structure became denser and more flocculated. Regression analysis revealed a strong correlation between fly ash content, soil expansivity, and CBR. The best regression equations were obtained for swelling (S = 0.297IP - 0.128FA) with an R² of 0.923, soaked CBR (CBR = 3.581 + 0.260FA - 0.194S) with an R² of 0.962, and unsoaked CBR (CBR = 5.296 + 0.457FA - 0.143IP) with an R² of 0.858. The resulting regression equations may serve as a preliminary predictive tool for estimating the CBR of clay soils stabilized with fly ash contents of up to 15%.