Application of lignin-based by-product stabilized silty soil in highway subgrade: A field investigation

Abstract

Lignin is a by-product of paper and timber industry, and it has not been fully utilized in both developed and developing countries. Improper disposal or storage of lignin is not only a waste of natural resources, but also posing significant risk to public health and the environment. Sustainable reuse options for lignin in civil engineering infrastructures, such as road embankments and dam foundations, have been recently evaluated by laboratory testing. However, up to now studies on the actual filed performance of lignin in stabilizing silty soils in highway subgrade have been noticed to be quite limited. With this in view, a field trial was carried out to verify the viability of using lignin stabilized silty soil as a highway subgrade course material. Traditional soil stabilizer, quicklime, was selected as a control chemical mixture in the field trial for comparison purposes. The construction procedures of the subgrade silty soil stabilized by lignin and quicklime in field Sections were presented. A series of field tests, including California Bearing Ratio (CBR) test, resilient modulus (Ep) test, Benkelman beam deflection test, and dynamic cone penetrometer (DCP) test were carried out after the subgrade construction to investigate the effects of the curing time and additive content on the mechanical properties and bearing capacity of the stabilized silt. In addition, moisture content and compaction degree tests were conducted to evaluate the quality of the compacted subgrade soils. The test results indicate that at the bottom zone of the filled soil layers with 96% degree of compaction, the 12% lignin stabilized silt exhibits superior mechanical performances (i.e., higher value of CBR and Ep, and lower values of resilient deflection (Hr) and DCP Index) than the 8% quicklime stabilized silt after 15 days of curing. Under the same additive content (i.e., 8%), the bearing capacity of lignin stabilized silt is slightly lower relative to the quicklime stabilized one. The field trial results reveal that as a stabilizer of the subgrade soil, lignin has negligible environmental influences and induces low construction costs. The use of lignin as a stabilization chemical mixture for silty soil may be one of the viable answers to the reuse of biobased organic by-product in civil engineering. The outcome of this study is of great significance for the development of nontraditional, cost-effective, and environmentally friendly soil stabilizer in solidification/stabilization technology.