Stabilization of marine clay subgrade with ferrochrome slag and calcium oxide: laboratory characterisation and Data-driven Prediction

Abstract

Marine clay subgrades are highly plastic, swell on wetting and have a low California bearing ratio (CBR), which makes them unsuitable for flexible pavements without improvement. This study examines the stabilisation of a high-plasticity marine clay (CH) from Kakinada, India, with ferrochrome slag (FCS), an industrial by-product, and calcium oxide (CaO). The clay was treated with 5–20% FCS to find the optimum slag content, and 1.0–2.5% CaO was then added to the optimum FCS mix. Differential free swell, Atterberg limits, modified Proctor compaction and CBR tests were carried out on nine mixes. The optimum contents were 15% FCS and 2.0% CaO. At 15% FCS, the plasticity index fell from 38.3% to 18.9%, the differential free swell from 80% to 52%, and the CBR rose from 1.13% to 6.10%. With 2.0% CaO added, the plasticity index fell to 12.0%, the differential free swell to 26% and the optimum moisture content from 33.02% to 10.23%, while the maximum dry density rose from 1.378 to 1.932 g/cm³ and the CBR reached 8.24%, which exceeds the 8% target adopted from IRC:37-2012 for capping layers. Linear and second-degree polynomial regression equations were fitted to relate the additive contents to the measured responses, and machine learning and Bayesian regression models were developed from the measured data for use within the tested range. FCS with a small dose of CaO is therefore a technically effective means of stabilising marine clay subgrades while reusing an industrial waste, although the findings are limited to one remoulded clay, and durability and chromium leaching remain to be evaluated.