Evaluation of mechanical behavior and microstructural studies of paper sludge ash-treated fine grained soil: A step towards sustainable building materials

It is well known that waste generation and its poor disposal practices have adverse environmental impacts. This study investigates a sustainable solution to improve soil properties using paper sludge ash (PSA), focusing on the physical, mechanical, and microstructural characterization of the stabilized material for building materials and field applications. Different tests were used to study the engineering characteristics of clay soil, which included standard proctor compaction, Atterberg limits, unconfined compressive strength (UCS) and pH. Besides, microstructural changes and mineralogical compositions were assessed using FESEM, XRD, and XRF. Effects of PSA content (0, 2.5, 5 and 10% by dry weight of soil), curing time (1, 7 and 28 days) and dry density (14, 15 and 16 kN/m 3 ) on properties of treated soil were considered. The results indicated that maximum dry density (MDD) decreased with increasing PSA content and curing time, whereas optimum moisture content (OMC) increased. As the PSA content and curing time increased, the plasticity index (PI) decreased. The results indicated that the UCS of the treated soil increased with higher PSA content, curing time, and dry density. The maximum UCS was observed in the 10% PSA-treated soil. Driven by extended curing time and increased dry density, this value showed a 19.94-fold increase compared to untreated soil. The treated soil exhibited an increase in pH with higher PSA content, whereas a downward trend was observed with extended curing time. Microstructural investigations indicated that the addition of PSA has modified the soil structure. Finally, the various statistical methods such as correlation, regression and sensitivity analyses were applied.