Introducing a sustainable method for stabilizing clay using industrial sludge ash and recycled polyethylene terephthalate fibers

In this study, the mechanical and shear properties of clayey soil stabilized with industrial sludge ash (SA) and reinforced with recycled polyethylene terephthalate (PET) fibers were investigated using tests including standard Proctor compaction, Atterberg limits, unconfined compressive strength (UCS), indirect tensile strength (ITS), direct shear, and ultrasonic pulse velocity (UPV) tests. The results of the compaction test showed that with the addition of SA, the maximum dry unit weight (MDUW) decreased by about 6%, and the optimum moisture content (OMC) increased by 11%. Also, the results of the Atterberg limit test showed that the liquid limit (LL) and plastic limit (PL) decreased by 19% and increased by 36% with the addition of 10% SA, respectively. Moreover, the results showed that the addition of 8% SA increased the UCS and ITS by 6.87 times and 9.3 times, respectively, compared to the unstabilized soil after 28 days of curing. Also, the addition of 0.7% PET fibers increased the UCS and ITS by 68% and 77%, respectively. Therefore, the optimum content of SA and PET fibers for mechanical properties was determined to be 8% and 0.7%, respectively. In the direct shear test, the shear strength of the samples increased by about 96% with the addition of 8% SA and 0.7% PET fibers. Also, the UPV of the stabilized samples with the optimum SA content increased by about 3 times. The highest UPV values were obtained at a PET fiber content of 0.4%. Therefore, while the optimum PET fiber content for mechanical and shear properties was 0.7%, the optimum fiber content for UPV was found to be 0.4%. Therefore, the combination of chemical stabilization with SA and reinforcement with PET fibers provides significant improvements in the mechanical and shear properties of the soil.