Characterizing geotechnical properties of sand subgrade soils stabilized with geopolymer based on metakaolin

Due to the detrimental ecological impacts and the exorbitant expenses associated with the cement industry , researchers have sought to find natural, sustainable, low-carbon alternatives to Portland cement for weak soil stabilization. This research used geopolymer based on metakaolin (MK), a natural pozzolanic material with different activator concentrations (NaOH and Na 2 SiO 3 ), to stabilize loose poorly graded sand soils. The research investigated the effect of different amounts of addition MK (5, 10, and 15 %) on the soil's mechanical properties . Furthermore, the effect of parameters such as the type and concentration of the alkaline solution and curing time (1, 3, and 7 days) on the unconfined compressive strength , failure strain, Young's modulus , California bearing ratio, and direct shear test were evaluated. This research also aims to measure the subgrade reaction modulus (Ks) by developing and manufacturing a laboratory testing apparatus and steel mold to simulate the natural conditions of sandy subgrade soil obtained from performing nonrepetitive static plate load tests. Additionally, scanning electron microscopy images (SEM) and X-ray diffraction analysis (XRD) were also used to study the microstructural changes and the chemical composition of the stabilized soil samples. The results indicate that the soil samples that were stabilized with MK 10 % and NaOH had notably higher compressive strength (2936 kPa), indicating a denser and less porous structure (improved stiffness stabilized soil) in comparison to the soil samples stabilized with MK 10 % and Na 2 SiO 3 which was (447 kPa). Ultimately, Microstructural analysis showed that, due to the addition of 10 % MK, stabilized soils have a denser and more homogeneous structure.