Strength properties, microstructural evolution, and reinforcement mechanism for cement-stabilized loess with silica micro powder

Natural loess has poor engineering properties because of its own loose and porous nature. To meet the needs of engineering construction, this study attempted to add silica micro powder mixed with cement into loess to improve its mechanical properties. The direct shear test, triaxial shear test, and scanning electron microscope (SEM) test were used to evaluate the strength characteristics and micropore structure modifications of silica micro powder and cement stabilized loess. The results showed that the addition of silica micro powder alone increased the shear strength of loess, while when silica micro powder was mixed with cement, the improvement in strength increased significantly. 3% cement with 10% silica micro powder is the optimum content to stabilize loess. The shear strength of the stabilized loess for 28 days under 200 kPa confining pressure was 2255 kPa, which was 34.9% higher than that of plain loess. Under the same cement content, the cohesion of loess increased with the increase of silica micro powder content, and the internal friction angle increased first and then decreased. The increase in curing age and the decrease in water content were positively correlated with shear strength, and the prediction formula of shear strength parameters of stabilized loess is established. In the SEM test, through qualitative analysis, it is found that the unreacted silica powder mainly physically filled the pores of loess, while the reacted silica micro powder and cement mainly combine with hydration products, which together enhanced the compactness of loess. From the quantitative analysis, it can be seen that with the addition of silica micro powder and cement, the macropores and mesopores between loess particles are transformed into small pores and micropores, the orientation of pores is enhanced, and the loess structure becomes more compact, which further revealed the mechanism of silica micro powder combined with cement to stabilize loess. The results of this study demonstrate that silica micro powder mixed with cement can effectively improve the mechanical properties of natural loess, providing a promising approach for reinforcing loess in engineering applications.