Effect of temperature on structure and mechanical properties of kaolinite via experiments and reactive molecular dynamics simulations

Abstract

To explore the temperature required for dehydroxylation of clay minerals and the properties of calcined clay in Limestone Calcined Clay Cement (LC3), this work took kaolinite as the research object. The chemical transformation of kaolinite after heat treatment was investigated by Thermogravimetric test (TG), X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Fourier Transform Infrared spectrum (FT-IR). Meanwhile, the internal mechanism of structural transformation and mechanical response was investigated by Reactive Molecular Dynamics (RMD) simulations. TG, FT-IR, and XRD analysis results showed that free water was removed at 378 K, dehydroxylation of kaolinite began at 673 K, and dehydroxylation was complete at 873 K. FT-IR analysis results showed that kaolinite tetrahedron remained stable, while octahedron changed. RMD simulations results showed that dehydroxylation of kaolinite began at 378 K ∼ 473 K, and kaolinite was transformed into metakaolinite at 873 K. And the results also showed that the formation of silanol (Si-OH) caused the peak of FT-IR to widen. The internal mechanism of the interlayer structural transformation of kaolinite was revealed through the analysis of layer spacing, interlayer adhesion work, interlayer water molecules, and H-bond. Eventually, RMD simulations results showed that metakaolinite had stronger deformation resistance than kaolinite by calculating the elastic constants.