Preparation, mechanism, and application of silica fume–steel slag composite cementitious material based on the D-optimal mixture method

Steel slag and silica fume as cementitious materials to replace cement have been subjected to many recent investigations. However, the optimization of the mix ratio of silica fume–steel slag composite cementitious materials has rarely been reported. This study aims to design and optimize a novel composite cementitious material of the steel slag–silica fume–ordinary Portland cement (SSP) using the D-optimal mixture design (DOD) method. A DOD model was developed to determine the optimal mix ratio of SSP. Microscopic tests were conducted to investigate the synergistic effect of SSP. The mechanical properties of SSP-stabilized macadam and stone chips were evaluated using unconfined compressive strength (UCS), water stability, and split strength tests. The results indicate that the optimal content of steel slag in SSP was determined to be 16.238%, and that of silica fume was 1.917%. Silica fume consumes the Ca(OH)2 generated during hydration, and as a filler, it also provides nucleation sites for hydration reactions, promoting the secondary reaction to generate calcium silicate hydrate (C–S–H) gels wrapped around the steel slag particles, optimizing the pore structure and reducing the porosity of SSP. The SSP promoted the development of mechanical strength in the later stages. The greatest growth observed in SSP-stabilized stone chips, from 7 days to 28 days of curing, the UCS, water stability coefficient, and split strength increased by 62.6%, 9.9%, and 71% respectively. A significant correlation was observed between UCS and split strength, with UCS being approximately 9.0 to 9.8 times higher than the split strength. This study contributes to the optimal design of similar solid waste composite materials and provides a reference for the use of silica fume and steel slag in road construction.