Strength Improvement of Dredged Marine Soil using Fly Ash and Cement: Evaluation and Mix Ratio Optimization

Dredged Marine Soil (DMS) is considered improper for use as a subgrade in roads due to high moisture content, low strength, and inability to withstand load. Additionally, there are concerns about the environmental aspects of disposing of DMS, thus necessitating the search for appropriate methods for sustainable use. Stabilization of soils with fly ash (FA) and cement has attracted interest as an alternative for upgrading existing soils with lesser use of conventional materials. This research explores the use of FA and cement to upgrade DMS, enhance its properties, and determine suitable mix ratios for subgrade construction in highways. Experiments in the laboratory involved DMS, both natural and stabilizing, with mixtures of FA and cement in ratios that give varying contents of these substances. The experimental methods involved Atterberg limit tests, Hydrometer tests, Specific gravity, Proctor compaction, Unconfined Compressive Strength (UCS), and California Bearing Ratio (CBR). Scanning Electron Microscopy (SEM) was also used to determine the microstructure, particularly the chemical composition and bonding properties. Curing times of 1, 3, and 7 days are considered when assessing the effect on the developed strengths. The result indicated that the amended DMS lacked sufficient strength and bearing capacity, thereby reaffirming that it cannot be used as subgrade material. But stabilization with FA and cement helped attain better results, especially with extended curing times. FA:Cement mix with a 50:50 ratio demonstrated strength beyond 400kPa and load-bearing capacity more than 20%, as specified by the Public Works Department (JKR). SEM analysis demonstrated that the microstructure appeared denser with less void content, confirming the cementation process responsible for the enhanced strength. Finally, using FA and cement for subgrade material stabilization is a viable alternative for sustainable subgrade construction on highways.