Molecular Dynamics Simulation Of Structure And Mechanical Properties Of Carbon Nanotubes Modified C-S-H Gel

Cement based composites are widely used in construction engineering.During the hydration process,cement will produce many different products,of which calcium silicate hydrate accounts for about 60% of the total hydration products,which has an important influence on the physical and mechanical properties of cement-based composites,and is an important object for people to study cement-based composites.Because of the complexity of the composition of hydrated calcium silicate gel,the microstructure remains controversial.The existing research shows that the microstructure of hydrated calcium silicate gel is similar to that of Jennite in the later stage of cement hydration.With the development of research scale,molecular simulation has become an effective tool to study material structure and predict material properties.In this paper,molecular dynamics method is used to carry out the following work(1)In order to simulate the atomic structure of hydrated calcium silicate gel,based on the structural parameters obtained from previous studies,a Jennite crystal model with calcium to silicon ratio of 1.5 was constructed by means of Materials Studio software.Geometric optimization and molecular dynamics(MD)modeling of the model were carried out.The elastic modulus is 25.46 gpa and Poisson’s ratio is 0.295.The results show that the Jennite crystal structure is suitable for the initial structure of calcium silicate hydrate,and can be used to predict other mechanical properties of hydrated calcium silicate gel.(2)Establish a molecular structure model of the interaction between carbon nanotubes and calcium silicate hydrate,and simulate the extraction process of carbon nanotubes in hydrated calcium silicate gel by molecular dynamics simulation.The displacement gradient is10 ?,With the withdrawal of carbon nanotubes,the pull-out of calcium silicate gel gradually increased from 0 to about 4200kcal/mol.The interaction energy gradually decreases from 303 kcal / mol to 0 due to the pull-out of CNTs.(3)Uniaxial tensile simulation of hydrated calcium silicate gel containing carbon nanotubes was carried out to study the effect of carbon nanotubes addition on the interface fracture of the composite model.According to the uniaxial tensile simulation of calcium silicate gel containing carbon nanotubes,the fracture of the composites mainly exists between the interlayers of silicate chains.When cracks appear in the composite sandwich,the CNTs can bridge both sides of the cracks effectively and continue to bear the stress until the whole system breaks.