Effects of Sodium Chloride Crystallization on Shear Characteristics of Road Base Aggregates under Unsaturated State

The precipitation and intrusion of sodium chloride into pavement structures is inevitable in coastal regions, which can affect the mechanical properties of the road base courses. To investigate this problem, samples with sodium chloride solution were cured in a thermostatic chamber until they reached the specified states of sodium chloride precipitation within the pores. A critical crystallization degree (ωc) was discovered by computerized tomography (CT) scan, corresponding to the start of formation of porous salt crust cementing the soil particles. A series of unsaturated large-scale triaxial shear tests was then conducted under various states of salt crystallization. The results showed that in the early stages of crystallization (i.e., ω<ωc), the peak stress and internal friction angle decreased with ω because of the coating and lubricating effects of salt powders, while the apparent cohesion remained constant. When ω>ωc, owing to the increasing adsorption and cementation effects of the salt crust, rapid growth was observed for the peak stress, internal friction angle, and apparent cohesion of the road base aggregates. Considering the influence of salt precipitation, a modified shear strength criterion that can predict the shear strength of the salinized road base aggregates was formulated.