Study On Mechanical Properties Of GN/GO Reinforced Cement Composite Based On Molecular Dynamics Simulation

With the development of the modern construction industry,the traditional cement-based composites is increasingly unable to adapt the building needs.In order to improve the mechanical properties of cement-based materials,many studies have shown that it is a feasible way to add graphene nanosheet(GN)/ graphene oxide(GO to cement-based materials,but it is expensive to study the enhancement mechanism and difficult to observe the phenomenon at molecular level by using experimental methods.Therefore,some scholars use molecular dynamics to solve this problem.Due to the numerous atomic models of calcium silicate hydrate(C-S-H),which is the main hydration product of cement,and the different force fields used in the simulation,the research results are different,so,more in-depth study is needed.In this paper,molecular dynamics method was used to study the mechanism of GN/GO reinforcing the mechanical properties of C-S-H,including the changes in tensile strength and Young’s modulus of composite materials,and the influence and reason of high temperature on the mechanical properties of GN/GO reinforced C-S-H were analyzed.The main research contents of this paper are as follows:(1)Established and validated atomic models of C-S-H,GN,and GO.Based on relevant researches,a real C-S-H model,and atomic models of GN and GO had been established.Then the ReaxFF force field was ued to conduct tensile simulation on each model,and compared results with previous researches.The results showed that:The established models and ReaxFF force field can accurately reflect the mechanical properties of various materials.(2)Analyzed the mechanism of GN/GO enhancing the mechanical properties of C-S-H.GN/GO was inserted into the C-S-H matrix and the structure and mechanical properties of the composite were studied using the ReaxFF force field.The results showed that: 1)Due to the poor binding between GN and C-S-H,the promotion effect of GN improving the tensile properties and Young’s modulus of C-S-H were not significant.2)GO can better improve the tensile strength and stiffness of C-S-H,because of the functional groups with GO can form the hydrogen bond network and related chemical bonds with C-S-H.3)During the tension processing of C-S-H,GN/GO can inhibit the development of microcracks.(3)Studied the effect of high temperature on mechanical properties of C-S-H,GN/C-S-H,and GO/C-S-H.The simulation temperature of each model were changed to conduct research.The results showed that: 1)GN/GO can stabilize the C-S-H structure.2)High temperature will destroy the hydrogen bond network of each composite structure,but adding GO can increase the number of hydrogen bond in C-S-H and reduced the reduction rate of hydrogen bond,while the addition of GN was the opposite.3)High temperature can reduce the mechanical properties of composite materials,but the addition of GO can improve the decrease in tensile strength and Young’s modulus of C-S-H.However,the improvement effect of GN on the reduction of tensile strength of C-S-H was not obvious,and even can reduce the stiffness of C-S-H.