Synergy of geopolymer and waste foundry sand in stabilizing lithomargic clay subgrades

In the context of road subgrade stabilization, this research explores the innovative application of geopolymer (GP) binder with Waste Foundry Sand (WFS) as chemical stabilizing additives. The aim is to enhance the engineering properties of lithomargic clay (shedi soil) found in the coastal Karnataka region of India. The study draws inspiration from prior studies on lithomargic and lateritic soil in the region, taking into account their unique challenges and vulnerabilities. The investigation focuses on the effectiveness of GP, which synthesizes slag and fly ash as integral binder precursors. The geopolymerization process is facilitated by an aqueous solution of sodium silicate-sodium hydroxide mix, serving as the chemical activating agent. This process involves cementation and chemical alterations within the soil matrix induced by GP, combined with mechanical stabilization using WFS. The study thoroughly examines and elucidates the enhanced compaction properties, Unconfined Compressive Strength (UCS), and California Bearing Ratio (CBR) values. Through Standard Proctor trials, the optimal GP dosage was determined to be with a Na2O-to-binder ratio of 3.0 %. Additionally, trials with WFS showed that 15 % of WFS resulted in a 30.65 % improvement in compacted density, along with substantial enhancements in UCS and CBR values. Furthermore, the study extends its insights into low-volume flexible pavement composition design, aligning with Indian standards. It presents a comparative analysis of performance disparities between selected stabilized and un-stabilized lithomargic clay. Durability studies, including prolonged strength (UCS, CBR) tests, wetting-drying repetitions, and freeze-thaw cycles, were conducted to gain confidence in the developed stabilization technique. Micro-structural analysis using scanning electron microscopy (SEM) clearly elucidated the mechanism by which GP-WFS stabilizes lithomargic clay. Overall, the incorporation of furnace slag, fly ash in GP production, and the inclusion of WFS in soil stabilization showcase its sustainable attributes, aligning with global efforts towards eco-friendly developments in pavement construction practices and resource optimization.