Effects of Temperature on Structural Properties of Hydrated Montmorillonite: Experimental Study and Molecular Dynamics Simulation

Wangbing Hong,Changdong Li,Shengyi Yan,Jie Meng,Xin He,Guobin Fu,Chong Xu

doi:10.1155/2020/8885215

Abstract

Montmorillonite (MMT) is highly sensitive to environmental changes and therefore plays a key role in the structural evolution of rocks and soils and even damage and disasters. The effects of important environmental factors (the temperature and water content) on MMT structural properties require in-depth study. The structure and morphology of sodium montmorillonite (Na-MMT) and its thermal products (micro-nanoparticles) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). A molecular dynamics (MD) simulation was performed to investigate how temperature (below the failure temperature of the Na-MMT crystal layer) affects the structural properties of hydrated MMT. (1) The laboratory results showed that increasing the temperature significantly affected water molecules, and the particle aggregates exhibited inhomogeneous thermal expansion. The interlayer structure collapsed at 500–700°C. (2) In the simulation, the pull-off force inhibited interactions among oxides, crystal layers on both sides of the sample, and the bonding structure of water molecules, thus exposing the stress on the bonding body for analysis. The MMT ultimate stresses in the X, Y, and Z directions all trended downward with increasing water content and temperature. (3) Environmentally induced damage was most likely to occur in the Z direction. Increasing the number of interlayer water molecules increased the layer spacing and considerably weakened van der Waals forces, such that the roles of the electrostatic force and the interlayer hydrogen bond network gradually became significant. The most significant impact of increasing the temperature was reflected in the hydrogen bonding network, resulting in the destruction of the interlayer water bridge, the gradual failure of the layered bonding structure, and the formation or development of cracks. This improved understanding of the structural properties of MMT aggregates under environmental change advances research on the evolutionary behaviour of nano-, micro-, and macrostructures of rocks and soils.

Highlights

Structural changes in rocks and soils under environmental change are often accompanied by damage and even disasters, posing potential hazards to human and property
Increasing the number of interlayer water molecules increased the layer spacing and considerably weakened van der Waals forces, such that the roles of the electrostatic force and the interlayer hydrogen bond network gradually became significant. e most significant impact of increasing the temperature was reflected in the hydrogen bonding network, resulting in the destruction of the interlayer water bridge, the gradual failure of the layered bonding structure, and the formation or development of cracks. is improved understanding of the structural properties of MMT aggregates under environmental change advances research on the evolutionary behaviour of nano, micro, and macrostructures of rocks and soils
A heating rate of 10°C/min was used to heat the samples to the prescribed temperature level, which was maintained for 1 h to ensure even heating of the specimens (Figure 1 shows the test samples diagrams of sodium montmorillonite and its heat-treated products). e heated samples were naturally cooled to room temperature and used for various laboratory tests, such as scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy

Summary

Introduction

Structural changes in rocks and soils under environmental change are often accompanied by damage and even disasters, posing potential hazards to human and property. E breakdown of aggregates leads to the expansion of existing cracks, the formation of new microcracks, and the structural collapse of minerals, thereby changing geotechnical properties. Humidity and temperature are environmental triggers that significantly impact the structure and physicochemical properties of many rocks and soils. Changes in humidity may trigger mineral dissolution-crystallization and structural expansion or contraction, leading to pore collapse, the development of existing cracks (pores), or the creation of new Advances in Civil Engineering cracks [5, 12,13,14,15,16,17], which in turn leads to the structural deterioration or even destabilization of rocks and soils. Frictional sliding in faults during accelerated slip leads to a large increase in temperature which thermally activates physicochemical processes. Friction during landslides can produce temperature increases above 800°C, which accelerates sliding [20, 21]

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Conclusion