COMPARITVE EVALUATION OF RECYCLED BENTONITE, FLY ASH AND CUTBACK ASPHALT FOR MITIGATING COLLAPSE POTENTIAL OF IRAQI GYPSEOUS SOILS

In arid and semi-arid regions of Iraq, and due to increasing urbanization, gypseous soils may dissolve upon wetting, resulting in much volumetric collapse and serious structural damage. An experimental analysis using a one-dimensional oedometer test was conducted using recycled materials, namely pile-drilling-induced bentonite, fly ash and cutback asphalt, to improve and mitigate the collapse resistance of gypsum-rich soils. The study aims to assess the effects of these additives on the settlement properties and their collapse potential. A total of twenty-one model collapsibility tests were performed at an inundation stress of 200 kPa on untreated (9.2, 21.5, 33% of gypsum percent) and treated soil samples with varying contents of additives, at 5, 10, and 15%. The current study shows that the water-holding capacity of soil is enhanced by the presence of bentonite, while fly ash promotes pozzolanic bonding and particle interlocking. The results also revealed the soil with 33% of gypsum content can be classified as problematic, while non- problematic case was found for the case of 9.2% based on the severity indication. Although each material plays a crucial role in improving the performance of gypseous soil upon wetting, fly ash has the edge over the rest; the collapse potential drops to 0.91% with 15% fly ash added for 21.5% gypsum. In brief, the recycled material has been confirmed as a sustainable stabilizer for gypseous soil, offering a viable alternative in problematic soils.