MULTISCALE CHEMICAL AND MINERALOGICAL IMPROVEMENT OF VERY HIGH PLASTICITY CLAY STABILIZED WITH NANO MATERIALS AND BIOPOLYMER

Abstract

Expansive soil, characterized by very high plasticity (CV) with Plasticity Index (PI) of  52.88%, poses a considerable challenge in geotechnical engineering due to its pronounced shrinkage-swelling behavior. It is influenced not only by index characteristics, but also by its chemical and mineralogical reactivity. Although PI has been used as an early parameter for expansive soil identification, but it has not been insufficient to explain the chemical and microstructural mechanisms on volume instability. This study proposes a multiscale chemical-mineralogical approach to complement PI-based evaluation through CV soil stabilization using nano-lime 3%, nano-silica 1%, and chitosan biopolymer 0.05%. Four treatment conditions were considered: untreated soil (CV), soil treated with biopolymer (CV+B), soil treated with nanomaterials (CV+N), and soil treated with a combination of nanomaterials and biopolymer (CV+N+B). The experimental tests were conducted using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM–EDS). FTIR results revealed Si–O absorption band shift from approximately 1040 cm⁻¹ in the untreated soil to approximately 970 cm⁻¹ in the nano–biopolymer treatment, indicating a calcium–silicate–hydrate (C–S–H) gel formation. XRD analysis confirmed the montmorillonite minerals' degradation, which was proved by reduced peak intensity in the 2θ = 5° – 8° range. XRF results showed increased CaO content, indicating a pozzolanic reaction at the bulk scale. SEM revealed microstructural densification and pore filling. EDS showed increased Ca/Si ratios, with statistical analysis confirming the nanomaterials–biopolymers combination as the most chemically effective. The study indicates that CV soil shows significant chemical reactivity with the nano–biopolymer system, with Ca/Si–C–S–H correlations functioning as a multiscale indicator enhancing conventional PI-based methods for assessing expansive soil identification.