Molecular Dynamics Simulation Of Mechanical Properties Of Calcium-silicate-hydrate

Cement is widely used in civil engineering.At the same time,the waste of cement-based materials and environmental damage are also very serious.The study of the main strength component of cement paste,which is calcium silicate hydrate(C-S-H),is beneficial to understand the strength mechanism and fracture characteristics of cement-based materials essentially.With the development of simulation technology and computer technology,the scale of researched materials has been extended from macroscopic to microscopic angles,from microscopic to nano-scale angles,and the application of molecular simulation technology has important practical significance in revealing and predicting the mechanical properties of materials.In this paper,the atomic models of amorphous C-S-H are reconstructed based on previous modeling process,and molecular dynamics simulations are carried out to study mechanical properties of amorphous C-S-H.Effects of temperature on mechanical properties of C-S-H structure under tensile/compressive loading in the layered direction are investigated via molecular dynamics(MD)simulations.Results show that: the tensile strength and Young's modulus of C-S-H structure significantly decreases with the increase of temperature;the water layer is an important factor affecting the tensile strength of C-S-H,so that the tensile strength of C-S-H is obviously less than compressive strength.Next,the effect of calcium-silicon ratio(C/S)on the mechanical properties of C-S-H under axial loading is studied.When silicon chain existing in C-S-H is in its complete form,the largest stress peak of C-S-H is reached and C-S-H has better tensile properties.When the C/S ratio was greater than 1.0,the free calcium atoms form calcium-oxide interaction at the defect caused by the lack of SiO2.To a certain extent,it can make up for the adverse effects of the deficiency of SiO2 on the system and play the role of bridging the silicon chain,making the tensile strength of C-S-H is not significantly decreased with C/S increasing.When water molecules were presented in the C-S-H,the presence of water molecules weakens the interaction between calcium and oxygen,which results in a decrease in strength of C-S-H,especially the tensile strength in z direction,and even a change in its failure mode.Finally,the dynamic mechanical response of C-S-H under shock compression loading in layered direction is studied.The shock Hugoniot curve and distribution of particles velocity are obtained by molecular dynamics simulation.From the analysis of the shock profile,it is found that the shock compression loading induces the material elastic,elastic-plastic and shock regime,and the Hugoniot elastic limit is about 7.5GPa.When particle velocity is below 0.5km/s,C-S-H is in elastic state,and only a elastic wave exists that belongs to a continuous wave.When the particle velocity is about 0.5km/s,the material begins to yield and a new wave begins to form.When the particle velocity is between 0.5km/s and 2.0km/s,a double wave structure composed of elastic precursor wave and subsequent plastic wave is formed,and the range of the elastic region is widened.When the particle velocity exceeds 2.0km/s,the phase transition wave has a dominant presence.These results provide important insights into the shock behavior of C-S-H in the layered direction.