Chemically Altered Natural Fiber Impregnated Soil for Improving Subgrade Strength of Pavements

This study explores the possibility of using sustainable materials in the form of natural fibers for reinforcing and improving the subgrade strength of pavements. Natural fibers with suitable biochemical properties were used for subgrade reinforcement in the past. Recently, the use of a waste weed, water hyacinth (WH), has garnered popularity as it can reinforce soil with the added advantage of waste utilization. It is well known that natural fibers have limited life when used in soils due to their degradation with time. For improving the longevity of the fiber and enhancing the mechanical performance of the soil-fiber composite, an effort was made in this study to chemically coat the natural fiber surface with nanoparticles of ferric hydroxide. The chemical coating can alter the short-term, as well as long-term, mechanical and chemical characteristics of WH fiber-impregnated soil, which is not well understood. The primary objective of the current study focuses on the short-term behavior of ferric hydroxide-coated WH fiber-impregnated soil that can be used as pavement subgrade. The effect of the chemical coating on WH fibers was initially analyzed by field emission scanning electron microscopy and energy dispersive X-ray tests. The impregnation of nanoparticle on the fiber surface increases surface roughness, coats the porous lumen of the fiber, and increases the tensile strength of the material. A set of tensile strength and moisture absorption tests was done for both untreated and treated WH fiber. The fiber tensile strength of treated fiber (TF) increased by 1.25 times as compared to untreated fiber (UF). The moisture absorption of TF decreased significantly from 580 % for UF to 255 %, indicating that the modified fiber became more hydrophobic. Unconfined compressive strength and direct shear tests were performed to evaluate the improvement in mechanical characteristics of chemically altered randomly distributed fiber-reinforced soil. The increase in cohesion, friction angle, and compressive strength at various compaction states has been discussed for soil reinforced with treated fibers (TF + S), untreated fibers (UF + S), and unreinforced soil (BS). For demonstrating the subgrade performance, soaked and unsoaked California bearing ratio tests were conducted on fiber-reinforced soil. For all the tests conducted on soil combinations (BS, (UF + S), and (TF + S)), the TF-reinforced soil composite performed the best. The results demonstrate the efficacy of using chemically altered natural fiber in increasing the subgrade strength of pavements.