Modelling the nanoscale properties of calcium silicate hydrate and ice

  • Amy Romaniuk

Student thesis: Doctoral Thesis

Abstract

Cement is the most widely used construction material in the world. It can sustain substantial load due to its high compressive strength but is vulnerable to cracks due to its quasi-brittle nature. Calcium silicate hydrate, the origin of strength in cement, is a complex, nano-crystalline material. An understanding of the structure-property relationships of calcium silicate hydrate at the nanoscale is of great importance in order to modify the structure for improved mechanical properties.;Molecular dynamics simulation studies are often used to investigate nanoscale materials and rely upon an accurate chemical structure and force field bonding description of the system. For cementitious materials, however, there is no established force field. ReaxFF, a reactive force field which can account for the creation and breaking of chemical bonds, has shown promise in the literature for simulation of the mechanical properties of calcium silicate hydrates. However, little evidence of validation of the force field for describing calcium silicate hydrates has been seen in the literature. Furthermore, the lack of experimental data for comparison makes validation of the simulation methods difficult.;One material which has been studied extensively both experimentally and in simulations, and is also of engineering importance, is ice Ih. In this work, ReaxFF is shown to make excellent predictions of the structure and physical properties of ice Ih and makes reasonable comparisons to experimentally measured elastic constants. A fracture simulation protocol has been designed and produces realistic values of fracture toughness and fracture speeds of ice Ih showing improvements over existing simulation studies.;By employing methods validated using ice Ih, this thesis goes on to predict the structure-property relationships of calcium silicate hydrate. It is revealed that the structure-property relationship is strongly correlated to chemical composition and therefore altering the ratio of the starting products in cement has the potential to lead to a product with tailor-made mechanical properties. Additionally, this thesis gives an insight into the tensile failure of calcium silicate hydrate at the nanoscale and highlights the challenges in simulating fracture such as the very high strain rate which must be adopted in simulations or the inability to model polycrystalline structures.
Date of Award17 Jan 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorShangtong Yang (Supervisor) & Leo Lue (Supervisor)

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