Utilization of olivine for soil stabilization

Soil stabilization is a common technique used for ground improvement. This promising technique uses cement and lime for construction purposes to enhance soil stability. However, binder production increases carbon dioxide (CO2) in the atmosphere per year. Therefore, sustainable materials for soil stabilization that are cost effective and not damaging to the surrounding soil upon treatment should be identified. Olivine [(Mg,Fe)2SiO4] is a sustainable material that can naturally capture CO2 in the atmosphere to form carbonated mineral. Furthermore, the chemical compositions of olivine are high amounts of magnesium oxide (MgO) and silicon oxide (SiO), as well as an adequate amount of silicon dioxide (SiO2), which make olivine a good candidate for soil stabilization in terms of hydration and pozzolanic reaction.This study aimed to address some issues about the use of olivine as a new sustainable material for soil stabilization through CO2 sequestration and in the presence of sodium hydroxide (NaOH), an alkaline activator. To identify the applicability of olivine-treated soil, the unconfined compressive strength (UCS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses were carried out on pure soil and olivine-treated soil before and after carbonation and in the presence of NaOH. The four specific objectives of this study are as follows. First is to investigate the mechanical and engineering behaviors of olivine-treated soil with different olivine contents at different curing times. Second is to determine the function of the carbonated olivine on the stability of soil at two different carbon pressures in different carbonation periods through the physical model in the laboratory.Third is to evaluate the effect of olivine in the presence of NaOH on soil stability and to identify the role of olivine as a source binder and NaOH as an activator of silicon and aluminum of olivine for soil stabilization at different curing times. Fourth and last is to examine the beneficial function of NaOH on the stability of carbonating olivine-treated soil at two different CO2 pressures with different carbonation periods based on geotechnical and microstructure analyses. In the first stage, mechanical and microstructure results confirmed that olivine changed the engineering properties of soil and increased soil stability up to 1.4 times more than untreated soil. In the second stage, the UCS of 20% olivine carbonated increased the strength of soil at high CO2 pressure after long carbonation period. The SEM analysis of 20% olivine-treated soil indicated that carbonated olivine decreased the soil discontinuity as a result of hydration and carbonation of MgO to produce Mg(OH)2 and MgCO3. The XRD analysis confirmed this indication. In the third stage, the results presented that the 20% olivine treated soil in the presence of 10 M NaOH increased the UCS of the soil after long curing time.Moreover, the SEM analysis confirmed the dissolution of olivine through the NaOH to have a homogenous soil structure. The EDX analysis demonstrated that when the Na/Al and Si/Al ratios increased, the soil strength also increased. The FTIR analysis showed the peaks of Si-O-Al, Si-O, Al-O, C-O, -OH, and H-O-H to establish the functions of NaOH and olivine as an activator and good source binder, respectively. In the final stage, carbonation of olivine-treated soil in the presence of NaOH at different pressures and different carbonation periods increased the strength of 20% olivine-treated soil to 6MPa. The following results were obtained: First, the use of 20% of olivine as a sustainable material for soil stabilization is noteworthy but it cannot sufficiently increase the strength of the soil. Second, the carbonation of olivine-treated soil increased the soil mechanical properties. Third, olivine acted as a source binder in the presence of NaOH to stabilize the soil. Finally, when the potential capacity of olivine carbonation in the presence of NaOH increased, the soil strength increased. This research discover that olivine can be used as a new stabilizer for soil improvement.

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