Abstract:

Expansive soil has strong swelling-shrinkage behavior. It swells and softens after absorbing water, and shrinks and cracks after losing water. These swelling-shrinkage behavior will seriously threaten engineering structures. In this study, the expansive soil was stabilized by rice husk ash (RHA) and ground granulated blast-furnace slag (GGBS). Through compaction test, unconfined compressive strength test, direct shear test, California bearing ratio (CBR) test, swelling test, scanning electron microscope test and X-ray diffraction (XRD) test, the mechanical strength, expansion characteristics and microscopic mechanism of solidified expansive soil were studied. Testing results show that the unconfined compressive strength of the stabilized soil with a ratio of RHA to GGBS of 6:4 and a 10% curing agent dosage is the highest among all stabilized soils. The mixture of rice husk ash-ground granulated blast furnace slag (RG) can reduce axial deformation and improve shear strength. With the increase of curing agent content, the cohesion of stabilized soil increases first and then decreases, and the internal friction angle increases gradually. Compared with the untreated expansive soil, the CBR value of the stabilized soil with RG can be increased to 7.9 times, and the mechanical strength of the soil has been significantly improved. RG can significantly reduce the swelling rate of expansive soil and the swelling force. The free swelling rate can be reduced from 11.4% to 0.5%, and the swelling rate with loading can be reduced from 1.1% to 0%. Additionally, the swelling force decreases between 12.1% and 62.8%. RG can promote the formation of flocculation, amorphous hydration products and a very small amount of ettringite (AFt), which are distributed on the surface of the soil and fill the pores so as to improve the strength of the soil and reduce the expansion of the soil. Meanwhile, RG can significantly diminish the hydrophilic minerals such as montmorillonite and illite in the soil and thus enhance the cementation between particles, thereby improving the strength and downgrading the swelling behavior of the expansive soil.

Key words: rice husk ash, ground granulated blast furnace slag, expansive soil, unconfined compressive strength, expansion characteristics, curing mechanism