Cement and concrete, acknowledged as the most globally utilized materials, possess mechanical characteristics intricately linked to their long-term durability. Despite centuries of use, a complete understanding of these materials remains elusive. Calcium silicate hydrate (C-S-H), a fundamental component of cement, serves as the primary binding agent, crucial in determining concrete strength. The hierarchical structure of C-S-H encompasses various strength-related attributes across multiple levels. Numerous studies extensively delve into the molecular-scale mechanical properties, yielding significant insights. Additionally, comprehending the material's microscale mechanical properties is essential for its engineering functionality. At the microscale, it can be envisioned as a granular substance with a cohesive-frictional solid phase, reminiscent of porous media.
Time-dependent deformation under constant loading (creep) is a significant factor in the long-term volume change of concrete, primarily occurring in calcium silicate hydrate (C-S-H) paste. Despite decades of research, accurately simulating such a complex phenomenon at the microscale remains challenging. For instance, molecular dynamics simulations typically deal with relatively small systems due to computational limitations. C-S-H exhibits complex nanostructures, requiring a larger scale to fully capture its mechanical behaviour. This complexity poses challenges in accurately representing its microstructure in finite element simulations.
In this study, a novel discrete element method based on solid mechanics was employed to model creep deformations in C-S-H and explore microstructure development during creep. Our simulations exhibit good agreement with nanoindentation creep tests, with detailed analysis conducted on the influencing factors affecting bulk mechanical responses. It was discovered that deviatoric stress, friction coefficient, and adhesion between surfaces significantly influence particle sliding, partially determining creep behaviours. These findings offer valuable insights into understanding the mechanism of creep in terms of microstructure change and can aid in nanoengineering C-S-H gels to minimize creep for enhancing concrete properties.
 

creep,C-S-H,discrete element method,solid mechanics,microstructure,nanoindentation