Impact of recycled macro-synthetic fibers on kaolin soil stabilized with lime kiln dust and volcanic ash

Soft clay soils inherently exhibit low mechanical strength, imposing significant challenges for various engineering applications. The present research explores various techniques and stabilizers to enhance soft clay's suitability for construction purposes. This study evaluates the mechanism of stabilizing kaolin using recycled macro-synthetic fibers (RMSF) for the first time. Samples were prepared with 5% LKD, with 25% replaced by VA, and varying RMSF amounts of 0, 0.5%, 1%, and 1.5% in lengths ranging from 4 to 6 mm. The specimens were cured for 7, 28, and 56 days and exposed to 0, 1, 4, and 10 freeze-thaw (F-T) cycles. Laboratory investigations were conducted through standard compaction, Unconfined Compressive Strength (UCS), Indirect Tensile Strength (ITS), Scanning Electron Microscope (SEM), California Bearing Ratio (CBR), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) tests on the samples at various stages of stabilizer addition, both before and after F-T cycles. The optimal mixture was 5% LKD, with 25% VA replacement and 1% RMSF, which led to a considerable 11-fold enhancement in ITS and a 14-fold improvement in UCS compared to the untreated sample. Additionally, the secant modulus (E50) and energy absorption capacity (Eu) of the sample with the optimal combination content increased in comparison to the stabilized sample without RMSF. The CBR of the optimal sample reached 81%, allowing for an 87% reduction in pavement thickness compared to the untreated sample. According to the findings of this research, the combination of LKD, VA, and RMSF increased the compressive and tensile strength properties, bearing capacity, and durability of kaolin, making it an appropriate option for use in various practical civil projects like road construction.