Study on the mechanical properties and durability of rice husk biochar and steel slag modified cement soil

In order to improve the mechanical strength of cement soil while reducing the environmental hazards associated with the disposal of steel slag (SS) and rice husk, this study investigates the effects of SS (with addition ratios of 0%, 5%, 10%, 15%, and 20% by dry soil mass) and rice husk biochar (RHB) (with addition ratios of 0%, 3%, 6%, 9%, and 12% by dry soil mass) on the mechanical strength and microstructure of cement soil through unconfined compressive strength (UCS) tests, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results indicate that, as the SS content increases, the UCS of cement soil increases first and then decreases, reaching its maximum at an SS content of 10% (SCS-10). Compared with the control group without SS (SCS-0), the UCS values at 7 and 28 days increased by 19% and 30%, respectively. The addition of RHB further enhanced the UCS of SS-modified cement soil, with the maximum value obtained at an RHB content of 9%. Compared with SCS-10, the UCS values at 7 and 28 days increased by 29% and 24%, respectively, while the UCS loss rates after 7 DW and FT cycles decreased by 45% and 32%, respectively. Microscopic results reveal that SS may increase the amount of C-(A)-S-H gel within the specimens, thereby optimizing their microstructure. Meanwhile, the addition of RHB may provides attachment and heterogeneous nucleation sites for hydration products, further promoting the growth of C-(A)-S-H and refining the microstructure of the specimens. This study demonstrates the potential of RHB to further enhance the strength and durability of SS-modified cement soil, providing a promising pathway for the combined resource utilization of SS and agricultural waste.