Cavitation thresholds in liquids, including comparison with experimental results at MHz frequencies: Lauterborn, W. Acoustica, Vol 22, No 1 p 48 (1969/70) (2370)

Abstract

Cement based materials are especially vulnerable to serious temperature changes in saline land or marine environments, resulting in the degradation of structures and properties. As the main binding components in cement based materials, the investigation of the C−S−H gel structure and water molecules behaviors enabled the detail damage mechanism of cement-based material under different temperatures. In this study, C−S−H gel models were successfully constructed with the final chemical formula of (CaO)1.65(SiO2)(H2O)1.79. Systematical research works were performed on the structures and properties of both C−S−H gel and water molecules in different local environments by molecular dynamics (MD) under temperatures ranging from 100 K to 500 K. Subsequently, the time correlation function (TCF) and mean square displacement (MSD) methods were introduced to explore the dynamic properties of various chemical bonds. The volume expansion of C−S−H gel under higher temperatures resulted from stretched bond length between silicon atoms and oxygen atoms, and variation of corresponding bond angles. In addition, higher temperatures promoted the prolonged hydrogen bond length, thus reduced the number of hydrogen bond. Moreover, the polarization of water molecules was weakened gradually under higher temperatures, but water molecules’ orientation fluctuated obviously along the out of plane directions of interlayer region. Additionally, MSD results revealed that water molecules showed temperature dependent diffusion behaviors in different chemical environments.