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UBC Theses and Dissertations

Heat curing method and laboratory performance evaluation of subgrade soil stabilized with bentonite and magnesium alkalinization Sabrin, Sohana


Alkalinization of problematic soils with silica and alumina rich material to improve their mechanical properties has become a popular practice globally. However, the application of alkalinization process to improve road bases and subbases namely subgrades are limited. Besides, the properties and performance of alkalinization process are dominated by several factors mainly initial curing conditions, concentration of alkaline activators and composition of materials. This study is aimed to investigate the effect of curing condition (temperature and duration) on unconfined compressive strength, elastic modulus (E50), microstructure and freeze thaw durability of silty sand subgrade soil stabilized with bentonite magnesium alkalinization. The selected curing temperatures and durations included ambient temperature, 40°C, 60°C and 80°C for 1 day and up to 3 days. Results revealed that curing at ambient temperature or as low as 40°C is not enough to achieve desirable strength while further increase in temperature favored substantial strength development. However, the properties of samples cured at elevated temperature for longer duration significantly deteriorated at later age (60 days) compared to the properties of samples cured at a slightly lower temperature. The optimal development of unconfined compressive strength and E50 observed when samples cured at 60°C for 3 days and the degree of improvement is 7 times compared to the natural soil. In addition, the scanning electron microscopy (SEM) images revealed presence of cementitious gel resulted from stabilization process. The data from energy-dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA) confirmed the presence of cementitious gel magnesium silicate hydrate (M-S-H) and calcium silicate hydrate (C-S-H) which made the samples more compacted and stable with time. Finally, higher unconfined compressive strength loss was observed during freeze thaw durability test but the samples were capable to withstand all 12 freeze thaw cycles.

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