Impact of lime treatment on the microstructure and geotechnical properties of micaceous soil

Abstract

Micaceous soils present significant challenges in geotechnical engineering due to their platy mineral structure, high compressibility and poor load-bearing capacity. The untreated soil examined in this study contained a high fraction of flaky mica and exhibited inherently weak engineering behavior, with an unconfined compressive strength (UCS) of approximately 45 kPa and low bearing resistance, rendering it unsuitable for direct use in pavement and embankment applications. Although the lime stabilization is widely adopted for improving fine-grained soils, its effectiveness and underlying mechanisms in mica-rich soils remain inadequately understood, particularly the relationship between micro-structural evolution and engineering performance. To address this gap, the present study systematically evaluates the influence of lime treatment on the mechanical and micro-structural behavior of micaceous soil. Soil samples were treated with 2%, 4%, 6% and 8% quicklime and cured for periods of up to 56 days, followed by evaluation of strength, compaction characteristics, consistency limits and micro-structural characteristics. The UCS increased substantially, reaching a peak value of 244.8 kPa at 4% lime after 56 days, representing an improvement of approximately 5.4 times compared to the untreated soil. The California Bearing Ratio (CBR) also peaked at the same lime dosage, with unsoaked CBR increasing from 3.65% to 9.34% and soaked CBR from 2.12% to 7.15%. Micro-structural analyses using SEM, EDS, XRD and FTIR revealed the formation of cementitious products, particularly calcium silicate hydrate (C–S–H) and calcium aluminates hydrate (C-A-H) phases, providing mechanistic insight into the observed strength improvements. The added value of this study lies in explicitly linking micro-structural transformations to macroscopic strength and bearing enhancement in lime stabilized micaceous soils, demonstrating that lime treatment can effectively upgrade problematic mica-rich soils to meet the engineering requirements for pavement sub-grades and embankment fills.