The increasing generation of industrial by-products has led to significant environmental concerns, including disposal challenges and the depletion of natural resources. Utilizing these by-products in construction applications offers a sustainable solution to mitigate waste accumulation while reducing the demand for conventional raw materials. This research comprehensively explores the utilization of cement slurry waste (CESW) combined with varying proportions (10 % to 70 %) of fly ash (FA) and bottom ash (BA) as potential materials for pavement subgrade applications. The mechanical behavior of these mixtures was evaluated through a series of unconfined compressive strength (UCS) tests on specimens prepared with different moisture contents and subjected to curing conditions within a desiccator and in ambient air for 7 and 14 days. Additionally, soaked and unsoaked California Bearing Ratio (CBR) tests and durability tests were conducted, along with repeated load triaxial tests, to examine the resilient modulus and deformation characteristics under repeated loading, simulating traffic conditions. Microstructural analyses, including scanning electron microscopy (SEM) and X-ray diffraction (XRD), were performed on the best-performing mix proportions to elucidate the underlying mechanisms driving strength enhancement. These micro-level investigations provided insights into the hydration reactions, pore structure refinement, and the role of ash in improving interparticle bonding. The experimental results revealed that the mixture containing 20 % FA or BA exhibited superior performance in terms of strength and durability. Samples with 20 % FA show UCS of 0.925 MPa, CBR of 48.5 %, and an average maximum resilient modulus (Mr) of 70.82 MPa. While samples with 20 % BA show UCS of 1.545 MPa, CBR of 53.2 %, and an Mr of 94.45 MPa, making it highly suitable for subgrade and subbase layers in pavement structures. Furthermore, the mixture with 30 % FA or BA has inferior mechanical properties but can be a good subgrade material. These findings demonstrate the potential of CESW-FA/BA mixtures as sustainable alternatives to traditional materials in pavement subgrade construction, contributing to both solid waste management and resource-efficient infrastructure development.
