Mechanical characteristics and solidification mechanism of slag/fly ash-based geopolymer and cement solidified organic clay: A comparative study

Geopolymers have recently received intensive research interests in the solidification of various soft soils due to their low-carbon footprint and environmentally friendly. However, understanding of the solidification characteristics of geopolymers in organic clay is still limited. In this study, a range of unconfined axial compression, pH value, moisture content, phase analysis, micromorphology, element composition and pore structure tests was conducted to comparatively investigate the physical properties and micromechanism of slag/fly ash-based geopolymer solidified organic clay (GSO) and cement solidified organic clay (CSO). Furthermore, the reinforcement effect of different parameters (geopolymer content and alkali-activator content) on the mechanical characteristics of GSO in the presence of humic acid was also investigated. The results show that the moisture content of CSO and GSO gradually increases with the content of humic acid, but the pH value and strength gradually decrease. Sustainable geopolymer is proven to be superior to cement in improving the physical-mechanical properties of organic clay. The unconfined compressive strength (UCS) of 28-day cured GSO2 containing 6% humic acid can reach 1.31 MPa, about 1.96 times of CSO1 containing 3% humic acid. The UCS of GSO can be significantly increased by the reasonable content of geopolymer and alkali-activator. Specifically, the 28-day UCS of GSO6 containing 20% geopolymer is 1.92 times and 2.68 times that of GSO2 (15%) and GSO5 (10%), respectively. The analysis of microscopic characteristics confirms that the strength formation of CSO and GSO is mainly affected by the number of cementitious products and the cementation degree of clay particles, which is attributed to the compactness of the matrix structure. The research results provide insights for a more comprehensive understanding of the application potential of geopolymers in organic clay solidification.