Use of Fly Ash as Weak Cementing Agent to Strengthen Marine Clay

Constructions on problematic soils are inevitable due to the increasing demand for land in the existing scenario. India has a coastline of 7500 km with large deposits of marine clay. Soft soils like marine clay are considered problematic due to its swelling behavior, low permeability, and highly compressibility. Landfill sites and reclamation areas formed due to dumping of dredged soft soils experiences high settlement and poor bearing capacity making it unsuitable as a foundation material. Atterberg limits represent the water holding capacity of soil. It can also contribute to estimation of shear strength, settlement, and permeability of soil. Researchers have explored various methods to reduce water holding capacity of marine clay and thereby enhance its engineering properties. Effective additives like fly ash, rice husk ash, marble dust, granite dust are widely mixed with marine soil to stabilize and improve its engineering behavior. Fly ash is a waste material produced in large amount at coal or lignite-based thermal power station. It requires large area of land for disposal as ash ponds as well as it causes air and water pollution. To address the adverse impact of dumping of fly ash on environment, wise utilization of fly ash is essential. In the present study, the effect of addition of Class F fly ash on liquid limit and plastic limit of marine clay and bentonite was studied. Marine clay obtained from Mumbai coast and bentonite from Kutch, Gujarat, was used in the tests. The liquid limit of the soil was determined using fall cone apparatus. Initially, the tests were performed on virgin clay only. Then the fly ash was added, and the percentage of fly ash in the soil was varied. The percentage of fly ash mixed in the soil ranges from 10 to 70%. The variation in liquid and plastic limit with the addition of fly ash was examined. It was observed that the plasticity index reduced by 60% in marine soil. Addition of fly ash reduced water absorption capacity of soil which in turn resulted in significant reduction in plasticity of soil. The usage of fly ash in improving clay with active minerals is novel and beneficial for reusing industrial waste products.