Optimization of Micromechanical Properties of Compressed Stabilized Earth Blocks Using Cement and Sewage Sludge Ash

This research explores the potential of sewage sludge ash (SSA) as a sustainable substitute option for cement in fabricating compressed stabilized earth blocks (CSEBs), enhancing both environmental sustainability and material performance. CSEBs are a sustainable alternative to traditional building materials, and the disposal of SSA, a by-product of urban wastewater treatment rich in heavy metals, presents significant challenges, particularly in regions like Bangladesh with limited landfill options. The research investigated the substitution of cement with SSA in 24 distinct mixtures, assessing their mechanical properties and sustainability. Blocks were prepared with varying contents of cement (4%, 6%, and 8% by dry weight of soil) and SSA additions (0%–50% by dry weight of soil). Findings indicated that blocks with up to 30% SSA, combined with 6%–8% cement, significantly improved in strength and durability. The optimal mix with 8% cement and 30% SSA achieved the highest dry compressive strengths of 5.42 MPa. The maximum wet compressive strength reached 6.39 MPa, slightly exceeding the dry strength due to extended hydration and pozzolanic reactions facilitated by water submersion. The samples also exhibited excellent water resistance, with only 10.16% water absorption, and minimal erosion and shrinkage confirmed superior durability, ensuring long-lasting, crack-resistant earth blocks. Further analysis using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of calcium silicate hydrate (C─ S─ H) gels, required for long-term strength. Additionally, X-ray fluorescence (XRF) tests indicated minimal heavy metal content, mitigating environmental risks. Life-cycle and cost assessments suggested that using SSA can reduce construction costs by 8.12% compared with traditional clay bricks, supporting the viability of SSA-enhanced CSEBs as a cost-effective solution for sustainable construction.