Revealing Expansion Mechanism of Cement-Stabilized Expansive Soil with Different Interlayer Cations through Molecular Dynamics Simulations

Abstract

Expansion of clay minerals in expansive soil, such as montmorillonite (MMT), is critical to a broad class of problems in science and engineering. Cement is one of the most widely used materials in the treatment of expansive soil. However, at present, the expansion mechanism of the soil treated by cement has not been thoroughly investigated at the nanoscale level. In this paper, four types of cement-stabilized MMT (Na-MMT, K-MMT, Ca-MMT, and Mg-MMT) molecular models with different interlayer cations and surface charges are established and validated by experimental data. The maximum adsorption energies of the four different cement-stabilized MMT systems are then investigated through molecular simulations, and the optimum water ratios are proposed for the four cement-stabilized MMT systems to achieve proper volume stability. The numerical simulations also show that the volume change of cement-stabilized MMT depends not only on the water-absorbing capacity but also on the CSH−MMT interface energy as well as the competitive absorption of CSH and MMT. For different types of expansive soil, Mg 2+ or K + modification may be used to improve the efficiency of the expansion control.

An Investigation on Mineral Dissolution and Precipitation in Cement-Stabilized Soils: Thermodynamic Modeling and Experimental Analysis

“…In the case of excessive doses, the further increased alkalinity promoted the dissolution of the soil minerals and the formation of the pozzolanic products, but the dissolution of the calcium-based clinkers was inhibited due to the excessively dissolved ions with smaller radii (Table 4), thereby limiting the hydrate formation and the growth of UCS. These facts aligned with the previous knowledge [1,42] that the performances of cement-stabilized soils are highly dependent on the total amount of CSH. Note that the supersaturation level of CSH in the JA12 specimen still exceeded that in the CS specimen within 10 h. This phenomenon was due to the acceleration effects of the high alkalinity on the reactant dissolution, during which the pore solution was unsaturated in the very early stages of the reaction.…”

The engineering properties and reaction mechanism of MgO-activated slag cement-clayey sand-bentonite (MSB) cutoff wall backfills

“…The reaction mechanism of MgO and GGBS blends has been investigated recently (Jin et al, 2015;Park et al, 2020), whereas the interactions between the MgO-activated GGBS, bentonite, and soil remain unresolved. It was reported that the backfill pH and saline cations affected the chemical stability of montmorillonite in bentonite (Jefferis 2012; Du et al 2020). For example, a high concentration of Ca 2+ could adversely impact the swelling properties of bentonite and then reduce the hydraulic conductivity (Wu et al 2019a).…”

Study of soil expansion characteristics in rainfall-induced red-bed shallow landslides: Microscopic and macroscopic perspectives

“…Jiang et al (2016) found that increasing the soil pH affected the stability of clay expansion and deformation [ 32 ]. Du et al (2020) found that different cation types have different effects on the expansion characteristics of clay minerals [ 33 ]. The reliability of the experimental results is again proven at the macroscopic scale.…”