Solidification of Subgrade Materials Using Magnesium Alkalinization: A Sustainable Additive for Construction

Abstract

The stabilization of problematic soils with chemical additives has become a popular practice globally. However, the mechanical and microstructural characterization of subgrade materials stabilized by alkalinization of raw silty sand, a common soil in British Columbia, Canada, has not yet been studied. This study introduces the novel concept of using an alkaline activator, along with magnesium chloride (MgCl2), to activate the silica and alumina components of silty sand. Compaction and unconfined compressive strength (UCS) tests were used to assess the mechanical properties of the stabilized soil. The mechanisms that have contributed to the stabilization process are discussed based on the results of microstructural analysis using field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) analysis. It was found that the chemical additive improved the compressive strength of the soil significantly. The UCS results revealed that a sample mixture containing an alkaline activator (sodium silicate/sodium hydroxide) ratio of .5, an alkaline activator to MgCl2 (L/S) ratio of .7, and 3% MgCl2 by dry weight of the soil was the optimum mix to improve the strength of the silty sand when cured for 28 days. The FTIR result confirmed the formation of the magnesium hydration products. Additionally, the SEM images and EDS data revealed that the stabilization process produced a cementitious gel, consisting of magnesium silicate hydrate (M-S-H) and magnesium aluminate hydrate (M-A-H) compounds, that bonded soil particles together.