UBC Theses and Dissertations

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UBC Theses and Dissertations

Development and evaluation of a new alkalinization additive for road subgrade stabilization Muhammad, Nurmunira


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 typical soil in British Columbia (BC), Canada, has not yet been studied. This study introduces the novel concept of using an alkaline activator, (a mixture of sodium hydroxide, SH (NaOH) and sodium silicate, SS (Na₂SiO₃)), along with magnesium chloride, L (MgCl₂), to activate the silica and alumina components of silty sand. This chemical mixture named as a magnesium-alkalinization (MA) additive. Compaction and unconfined compressive strength (UCS) tests were used to assess the mechanical properties of the stabilized soil. The development of the MA additive was then used as a substitute component for developing the new chemical additive, which utilized a local bentonite product. The additive developed from the mixture of bentonite, MgCl₂, and alkaline solution was introduced for stabilization of soil. The mechanical and physicochemical results revealed that the addition of 40% bentonite was the optimum content for improving the strength of silty sand, which was then named as the bentonite-magnesium-alkalinization additive (BMA). The investigations on the mechanism of strength improvement were carried out on the optimum designed sample, based on microstructural analysis using X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The microstructure analysis confirmed the formation of the cementitious products, such as calcium aluminate silicate hydrate (C-(A)-S-H) and magnesium silicate hydrate (M-S-H) in the treated sample. Further investigations on the effect of curing temperature for BMA additive revealed the optimal development of UCS occurred when samples were cured at 60°C for 3 days. The degree of improvement was 7 times compared to natural soil. Further studies on the resilient modulus (MR) and suction (s) relationship were also performed for the silty sand stabilized with the optimum design of the BMA additive using the normalized model. As a result of the MR-s relationship analysis, seasonal variation is a crucial factor that should be considered when constructing flexible road pavement even for the stabilized soil.

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