In order to reuse granulated blast furnace slag (GBFS) and low-strength soft clay (SC), this study developed a curing material using magnesium oxide (MgO) as an alkali activator to excite the GBFS and basalt fiber (BF) as reinforcing material to prepare the SC. The mixing ranges of GBFS, MgO, and BF were established as 9.48%~14.52%, 0.48%~5.52%, and 0%~1.00454% of the dry clay mass, respectively, and the mixing ratios of the three were optimized using the central composite design (CCD) test. Through the analysis of variance, factor interaction analysis, and parameter optimization of the CCD test, the optimal mass ratio of GBFS, MgO, and BF was determined to be 13.35:4.47:0.26. The curing material of this ratio was named GMBF and mixed with SC to prepare GMBF solidified clay. An equal amount of ordinary Portland cement (OPC) was taken and formed with SC to form OPC solidified clay. The mechanical properties, durability, and hydration products of GMBF solidified clay were clarified by the unconfined compressive strength (UCS) test, freeze–thaw cycle test, X-ray diffraction (XRD) test, and scanning electron microscopy (SEM) test. The UCS of the GMBF solidified clay was 1.08 MPa and 2.85 MPa at 7 and 91 days, respectively, which was 45.9% and 33.8% higher than that of the OPC solidified clay (0.74 MPa and 2.13 MPa) at the same curing time. After ten freeze–thaw cycles, the UCS of GMBF and OPC solidified clay decreased from the initial 2.85 MPa and 2.13 MPa to 1.59 MPa and 0.7 MPa, respectively, with decreases of 44.2% and 67.1%, respectively. By XRD and SEM, the hydration products of GMBF solidified clay were mainly calcium silicate hydrate gel and hydrotalcite. The interface bonding and bridging effect formed between BF and SC or hydration products, indicating that these interactions contributed to the solidified clay enhanced structural integrity. This study demonstrates that the CCD approach provides solution for recycling SC and GBFS. Laboratory tests confirm the potential of the optimized GMBF formulation for practical engineering applications. [ABSTRACT FROM AUTHOR]

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