A molecular dynamics study on kaolinite-water-CMC mixture for 3D printing applications

Clay materials are widely distributed on Earth, but their sensitivity to water has limited their use as building materials (rammed earth, molded or 3D printed earth). As a family of inorganic layered nanomaterials, understanding clay’s atomic-scale mechanical behavior is crucial for uncovering its macroscopic properties, and environmental interactions and using it effectively as a building material. In this study, a hydrated kaolinite model was constructed using molecular dynamics, incorporating carboxymethyl cellulose (CMC) molecules. The microstructure and interfacial stick–slip friction behavior of two atomics models under varying confining pressures were examined. The results indicate that interlayer spacing gradually decreases with increasing confining pressure. At higher water pressures, interlayer water molecules reach an almost stagnant state, while at lower pressures, the water molecules in the kaolinite-CMC system exhibit higher activity. Both models display stick–slip behavior during shear processes, and comparisons of stress–strain curves at different shear rates suggest that CMC reduces the model’s average shear force. The presence of CMC increases the interlayer spacing of kaolinite, thus decreasing cohesion and the friction angle of the model. Additionally, the effectiveness of CMC additions improves with increasing shear rates. Finally, the results of this research could be used to understand the rheology of raw earth with bio-sourced materials mixture in 3D printing applications or rammed earth applications.