Microstructural and mechanical properties of kaolin stabilized with cement, ground-granulated blast-furnace slag, and nano-silica

This study presents the effect of different ground granulated blast-furnace slag (GGBS) contents (5, 10, 15, 20, and 30%) on constant cement and nano silica (NS) (7.5% and 1%, respectively)- treated kaolin. A laboratory testing program was conducted, including Atterberg limits, compaction, consolidation, unconfined compression (UCS), and California bearing ratio (CBR) tests, along with microstructural analyses using field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), and X-Ray diffraction (XRD). The long-term mechanical response was investigated using 7-, 28-, and 365-day-cured specimens in UCS tests. The results of fresh-state specimens showed that the liquid and plastic limits of clean kaolin increased with the addition of GGBS. With the addition of 7.5% cement-1% NS and 30% GGBS, the liquid limit and optimum water content (w opt ) of clean kaolin increased by 25% and 39.33%, respectively. Void ratio, compressibility (C c ), and swelling (C s ) indices increased with cement, NS, and GGBS additions. Unconfined compressive strength (q u ) of clean kaolin increased with additives and curing days. At 7 days of curing, 7.5% cement and 1% NS additions improved the q u value of clean kaolin by 681.3%. The q u values of some specimens cured for 365-days showed an increase of over 100% compared to their 28-day-counterparts. Similarly, CBR values exhibited a significant increment with GGBS additions, reaching around 300% with 7.5% C-1% NS and 30% GGBS additions. FT-IR and XRD analysis of clean kaolin and treated materials showed a transition from a crystalline structure to an amorphous structure. FE-SEM analyses demonstrated the gel-like products within the soil matrix. Consequently, the microstructural tests suggested that the improvement occurring at the macro scale arises from micro-mechanical changes at the particle scale. This study, therefore, presents new insights into the bridge between micro and macro-observations and the long-term response of kaolin treated with reactive mineral additives, including GGBS, cement, and NS.