Molecular Dynamics Simulation Of Mechanical Properties Of Calcium-silicate-hydrate/graphene Oxide Composites

As the most important product of cement hydrates,calcium- silicate-hydrate gel(C-S-H) has great influence on microstructure and macroscopical properties of cementitious materials and has become the integrant issue on cement-based materials research.C-S-H gel is amorphous at room temperature and people still have dispute of its molecularstructure. Butin correlation study,C-S-H gel has high similarity with some naturalmineral,such as tobermorite and jennite.As the derivative of graphene, graphene oxide(GO) has high flexibility,large specific surface area and excellent mechanical properties.GO structure contain some hydrophilic groups,such as hydroxyl group(-OH), carboxyl group(-COOH),epoxy group(-O-),etc.GO is water-soluble and have significantly enhanced toughening effect for some polymer materials and inorganic non- metallic materials,etc.GO has the feasibility of enhanced toughening effect on concrete from the analysis of its structure and performance.There are some relevant experiments to verify it.We have built four incipient modles in this article:C-S-H, GO, C-S-H/GO composites and C-S-H/GO interface.After relevant processing and molecular dynamics,we simulate and calculate their mechanical properties.The main results are as follow:①The choice of the calculation module,the difference of ensemble and forcefield, the difference of single crystal cell and supercell have certain effect on the calculation results of C-S-H gel.The results under NPT ensemble are bigger than that under NVT and NVE ensemble. When single crystal cell expand to supercell,the result is closer to the actual value.The results of 14? Tobermorite and Jennite 2×2×2 supercell under NPT ensemble are relatively close to the nano indentation result.The results of 11? tobermorite and jennite model have a better agreement with the literature value.②The average Youngmodulus of those amorphous periodic unit cells which containing 2、3、4、5 GO(II)moleculars is 139.22 Gpa.③After relevant processing and molecular dynamics to the C-S-H/GO composites model,graphene oxide adsorb to the surface of hydrated-calcium-silicate.The highest Young modulus of C-S-H has increased by 52.9% after the addition of graphene oxide and with the increase of graphene oxide content, the Young modulus of C-S-H will also increase under NVT ensemble.The choice of ensemble is important to the simulation results of C-S-H/GO composites. The Young modulus of C-S-H does not increase under NPT and NVE ensemble.④The binding energies of difference C-S-H surface and GO are all positive,which indicates that they are attracted to each other.The magnitude of the binding energy have a relationship: C-S-H(1 0 0)>C-S-H(0 0 1)>C-S-H(1 0 0)>C-S-H(1 1 1).When the size of C-S-H surface increase,the binding energies of C-S-H surface and GO is bigger.