Nanoscale mechanism on lime stabilization of expansive soil

Expansive soil is blamed for many engineering problems such as foundation damages, subgrade heave, and road surface bulking. Lime is one of the most widely utilized materials in the stabilization of expansive soil. However, the stabilization mechanism of lime-treated expansive soil has not been thoroughly studied from the nanoscale level. This paper employed montmorillonite (Mt) and portlandite (Po) to represent expansive soil and the hydration product of lime. Four types of portlandite-montmorillonite (Po-Mt) molecular models with different surface charges and interlayer cations revealed the nanoscale stabilization mechanism of Po-Mt. The results show that volume change of Po-Mt samples is not only related to adsorption energy of Mt, but also controlled by competitive adsorption of Po and interaction between lime and Mt. The interface energy between Po and Mt generated by Ca ions migration from Po to Mt surface plays a most significant role in governing the swelling behavior of Po-Mt by providing strong repulsive force to confine the swelling of Mt layers.