Mechanical properties and mechanisms of soft clay treated by all-industrial by-product binder in alkali-sulfate activating framework

Soft clay treatment with all industrial by-product (IBP) binder has great economic and environmental benefits, yet its geomechanics and mechanisms still need to be well probed. With the activation by calcium carbide residue (CCR) and phosphogypsum (PG), the strength, structure, and mechanisms of soft clay treated by aluminosilicate-rich IBP (AS-IBP, such as ground granulated blast furnace slag (GGBS), fly ash (FA), coal gangue (CG), Bayer red mud (BR), and sintered red mud (SR)) are comparatively investigated. The strength characteristics of solidified clay exhibit significant differences as AS-IBP changes. When GGBS is adopted, the strength is sensitive to the change in PG content, while the impact of CCR is insignificant. After 90 d, the strength of the optimal sample (G23) reaches 1.40 MPa, 35.9% higher than cement solidified clay (CSC), while that achieved by other AS-IBPs is less than 0.3 MPa. In the compression test, the structure's evolutionary trend of G23 has a sudden change as the strength increases from 1.81 MPa to 2.29 MPa, suggesting the transformation in material properties. Besides, the structure of G23 is stronger than CSC, which contributes more to the compressive performance. The total amount of main products (C-S-H and ettringite) of all-IBP solidified clay determines the strength, and ettringite is only significant when calcium-rich AS-IBP is adopted. The total amount of minor products (C-A-H and C-A-S-H) is similar for different samples, equivalent to 28.9%–46.3% of the main products. The relationship between the strength and the product amount can be presented using an exponential function.