Micro-structural analysis of strength development in low- and high swelling clays stabilized with magnesium chloride solution — A green soil stabilizer

• Interaction between magnesium chloride solution and clayey soils
• Shear strength and micro-structure of unstabilized and stabilized clays
• Role of MgCl2 concentration and curing time on strength development
• M-S-H and M-A-H, cementitious products of stabilized bentonite and kaolin

Although the effects of chemical additives on the geotechnical properties of soils have been investigated in recent years, the strength properties and micro-structural characteristics of clayey soils stabilized with magnesium chloride (MgCl2) solution, a green soil stabilizer, have not been clearly brought out. The objective of this study is therefore to investigate the time-dependent engineering properties, mineralogy, morphology and molecular characteristics of MgCl2 stabilized tropical fine-grained soils. Bentonite and kaolin, which represent high and low swelling clays, respectively were employed as the soils tested in this study. Compaction, unconfined compression strength (UCS) and standard direct shear tests were undertaken to assess the engineering properties of the stabilized clayey soils. The mechanisms that may have contributed to the stabilization process were discussed based on the micro-structural analysis using different spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometry (EDAX), Fourier transform infrared spectroscopy (FTIR) and Brunauer, Emmett and Teller (N2-BET) surface area analysis. From an engineering point of view, the MgCl2 improved the compressive strength of the bentonite and kaolin significantly. The 7-day UCS of MgCl2 stabilized bentonite and kaolin were approximately 2 times higher than that of unstabilized ones. The micro-structural study revealed that the stabilization process modified the porous network of the tested clayey soils. The pores of the soils had been filled by newly formed crystalline compounds known as magnesium silicate hydrate (M-S-H) and magnesium aluminate hydrate (M-A-H) for the bentonite and kaolin, respectively.