The Influence Mechanism of Ettringite Crystals and Microstructure Characteristics on the Strength of Calcium-Based Stabilized Soil

To reveal the influence mechanism of ettringite (AFt) crystals and microstructure characteristics on the strength of calcium-based stabilized soil, the strengths and microscopic properties of seven groups of stabilized soil samples were studied systematically through unconfined compressive strength, scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TG), and Fourier transform infrared spectroscopy (FTIR) testing methods. The results indicate that the strength of the cement-stabilized soil is relatively high because abundant calcium silicate hydrate (CSH) gels coat the outer surface of soil particles to cement together. For the cement–gypsum-stabilized soil, superabundant thick and long AFt crystals make the pores in soil particles larger, and the sample becomes looser, resulting in lower strength than that of the cement-stabilized soil. However, the strength of the cement–gypsum–lime-stabilized soil is slightly stronger than that of the cement-stabilized soil, for the reason that the appropriate amount of fine AFt crystals fill the macropores between soil particles to form a network space structure and sufficient CSH gels cement the soil particles and the AFt crystals network space structure tightly together. It could be suggested that the components of calcium-based stabilizer should consider the optimal production balance between CSH gels and fine AFt crystals.