Mechanical and Bearing Performance of Cement–Fly Ash Stabilized Clay Subgrade

Denny B. Pinasang; Miswar Tumpu; Don R. G. Kabo; Carter Kandou; Herman Tumengkol; Hoong Pin-Lee

doi:10.48084/etasr.17751

Authors

Denny B. Pinasang Civil Engineering Department, Manado State Polytechnic, Manado, Indonesia
Miswar Tumpu Disaster Management Study Program, The Graduate School, Hasanuddin University, Indonesia
Don R. G. Kabo Civil Engineering Department, Manado State Polytechnic, Manado, Indonesia
Carter Kandou Civil Engineering Department, Manado State Polytechnic, Manado, Indonesia
Herman Tumengkol Civil Engineering Department, Manado State Polytechnic, Manado, Indonesia
Hoong Pin-Lee Civil Engineering Department, Faculty of Engineering and Quantity Surveying, INTI International University, Negeri Sembilan, Malaysia

Volume: 16 | Issue: 3 | Pages: 35912-35919 | June 2026 | https://doi.org/10.48084/etasr.17751

Received: 25 January 2026 | Revised: 5 March 2026 | Accepted: 13 March 2026 | Online: 6 June 2026

Corresponding author: Denny B. Pinasang

Abstract

Clay soils with low bearing capacity pose significant challenges for road pavement subgrade performance, especially in moisture-sensitive environments. This study evaluates the effectiveness of cement–fly ash mixtures for soil stabilization to improve the engineering properties of clay used as a subgrade layer. Laboratory experiments varied the fly ash content (0%, 5%, 10%, 15%, and 20%) while keeping the cement proportion fixed. The stabilized soils were evaluated using Atterberg limits, compaction characteristics, and California Bearing Ratio (CBR) tests. The results show that using cement–fly ash mixtures reduces soil plasticity while increasing maximum dry density and bearing capacity. Optimal performance was observed at 15% fly ash, which produced a significant improvement in CBR compared with untreated soil, whereas higher fly ash contents yielded diminishing strength gains. This study identifies an optimal cement–fly ash combination that improves mechanical performance while maintaining material efficiency, supporting sustainable pavement design. The findings also demonstrate the potential to use industrial by-products to reduce dependence on conventional materials, contributing to the Sustainable Development Goals (SDGs), particularly SDG 9 (Industry, Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities), and SDG 12 (Responsible Consumption and Production). The results provide practical guidance for engineers and policymakers in developing cost-effective and environmentally responsible road infrastructure.

Keywords:

clay soil stabilization, cement–fly ash stabilization, subgrade improvement, CBR, sustainable pavement design, industrial waste management, SDGs

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