Simulation of calcium silicate hydrate gel using the molecular dynamics method

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Simulation of calcium silicate hydrate gel using the molecular dynamics method

ارائه دهنده: Provider: Erfan Taheri

اساتید راهنما: Supervisors: Amir Rezaei Sameti (Ph. D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr nili and Dr rezaei

زمان و تاریخ ارائه: Time and date of presentation: 2026

مکان ارائه: Place of presentation: 44

چکیده: Abstract: Calcium–silicate–hydrate (C–S–H) gel, as the dominant phase in the microstructure of Portland cement concrete, plays a decisive role in governing the mechanical properties, durability, and long-term stability of this material. This phase exhibits a nanostructured, disordered morphology and is highly sensitive to environmental variables. In many civil engineering applications—particularly structures in direct contact with aqueous environments, such as concrete dams, underground tunnels, storage reservoirs, and marine infrastructures—C–S–H gel is subjected to significant hydrostatic stresses. Under such loading conditions, pressure is applied uniformly from all directions to the material structure. The simultaneous presence of hydrostatic loading with temperature fluctuations, moisture variations, and chemical reactions renders the mechanical behavior of C–S–H gel a complex, multivariable phenomenon, the experimental investigation of which at the laboratory scale is associated with substantial challenges. In this study, the volumetric and mechanical behavior of C–S–H gel under hydrostatic loading was comprehensively investigated through an atomic-scale numerical approach using molecular dynamics simulation. Atomic models of C–S–H gel were constructed and analyzed over a range of eight calcium-to-silicon (C/S) ratios, five relative humidity levels, and six distinct temperatures. The mechanical response of the gel was evaluated through analysis of hydrostatic pressure–volumetric strain curves, pressure–bulk modulus relationships, pressure–compressibility trends, and variations in interatomic bonding. The results indicate that high moisture content and intermediate temperatures (300–500 K) enhance structural mobility, reduce bulk stiffness, and increase the compressibility of the gel. Elevated hydrostatic pressure exerts a dominant influence on gel behavior; with increasing pressure, the differences in response among samples under varying environmental conditions diminish. Intermediate C/S ratios (approximately 1.5–1.9) exhibit optimal mechanical performance, characterized by greater structural stability and higher load-bearing capacity, whereas very low or very high C/S ratios lead to increased compressibility and reduced uniformity in the volumetric strain–pressure response. Anisotropic behavior of the C–S–H gel was observed even under hydrostatic loading, such that strains along the z-axis were generally greater than those along the x and y directions and showed higher sensitivity to changes in moisture and temperature. Increasing moisture and pressure reduced anisotropy and improved mechanical performance, whereas elevated temperatures increased axial strain in the z-direction and reduced the overall resistance of the gel.