Strengthening montmorillonitic and kaolinitic clays using a calcium-based non-traditional additive: A micro-level study

Chemical stabilization of clays is commonly used to improve unfavorable engineering properties. Though the effects of non-traditional additives on soil improvement have been investigated in recent years, documented research studies on the macro- and micro-level characteristics of problematic clays stabilized by non-traditional additives are fairly limited. The current study examines the time-dependent changes induced in the strength, mineralogy, morphology, molecular and micro-fabric characteristics of montmorillonitic and kaolinitic clays stabilized with a non-traditional calcium-based additive, which is commercially available under the product name SH-85. The physico-chemical bonding mechanisms induced by the stabilization process were studied at a micro-level using various spectroscopic and microscopic techniques, such as X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometry (EDAX), Fourier transform infrared spectroscopy (FTIR), Brunauer, Emmett and Teller (BET) surface area analysis and particle size analysis (PSA) using a laser diffraction approach. Unconfined compressive strength (UCS) tests were also performed on stabilized specimens at various curing times to examine macro-level characteristics. The UCS test results showed that the 6% and 9% additive content were optimal for montmorillonitic and kaolinitic clays, respectively, with the UCS of both stabilized clays improving significantly after 7 days of curing. This relatively rapid curing reaction process is very advantageous and cost-effective for geotechnical engineering applications. The micro-level study revealed that the calcium-based additive modified the porous network of the stabilized clays. The pores were filled and particles were bonded by cementitious products, including calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) for the stabilized montmorillonitic and kaolinitic clays, respectively.