Experimental study on the mechanical properties of fly ash stabilized bentonite via sodium hydroxide-geopolymerization process

Expansive clay is problematic for transportation infrastructures due to its vulnerability to water induced decrease in strength. Building on existing geopolymer stabilization techniques, this study focuses on optimizing the mix design for expansive soils and elucidating the key physicochemical mechanisms involved in the geopolymerization process to enhance the stabilization performance. To do so, a series of uniaxial compression tests was conducted on a bentonite treated using combination of fly ash and sodium hydroxide (NaOH) while considering different fly ash content, NaOH concentration and initial moisture content. The physical-chemical mechanism of geopolymerization process was investigated using a combination of X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) analysis as well as scanning electron microscope (SEM) observation. An emphasis was made on the effect of NaOH concentration. Experimental results show that NaOH concentration has the most significant impact on the strength of treated bentonite, which is followed by moisture content and fly ash content. With increasing the NaOH concentration, an optimum NaOH concentration exhibits and corresponds to the maximum unconfined compression strength (UCS) of the treated bentonite. This behaviour can be explained by a different competition of cation exchange reaction and the formation of geopolymer gel. This means that the formation of geopolymer gel may be hindered in high NaOH concentration.