Numerical Simulation And Experimental Study On Mechanical Properties Of Graphene Oxide Modified Cement-based Composites

Cement-based composite materials(concrete,mortar,etc.)are currently one of the most commonly used materials in construction and infrastructure construction.With the excellent engineering mechanical properties and price advantages,it has become the most widely used and most important building structure material at present.However,cementbased composites have non-negligible defects(poor crack resistance,low tensile strength and strain capacity)and have typical brittle material properties.High brittleness can cause problems such as cracks and penetration,and in practical engineering applications,this often leads to a large number of cracks on the surface of the structure.Thereby affecting the mechanical properties of the structure and reducing its service life.However,graphene oxide(Graphene Oxide,GO),an oxide derivative of nanomaterial graphene,not only has higher surface area,high strength and good toughness,but also contains a large number of oxidized functional groups on the surface,which is hydrophilic.It can regulate the hydration products of cement-based composite materials,and at the same time fill pores to form a denser structure.This is expected to fundamentally prevent the formation and propagation of micro-nano-scale cracks and improve the mechanical properties of cement-based materials.At the same time,because of the large number of oxidizing functional groups attached to the surface of GO,it is easy to react with the main hydration product of cement,calcium silicate hydrate(CSH),which makes the interface between GO and CSH have a great bond strength,so research In the mechanical properties and interaction mechanism of GO modified cement-based composites,the mechanical properties of the interface between GO and CSH play an important role in their mechanical properties.In this paper,molecular dynamics simulation,finite element simulation and macroscopic experiment were used to study the mechanical properties of GO-modified cement-based composites.Firstly,a periodic GO molecular model with oxygencontaining functional group coverage R=50% and OH:O=2.0 was established,and its average Young’s modulus was calculated to be 232.35 GPa through molecular dynamics simulation.Through the tensile simulation of the multilayer GO model,the simulation results show that the Young’s modulus of GO will decrease with the increase of the number of layers.Compared with the single-layer GO,the Young’s modulus of the 8-layer GO is reduced by about 20%.Through the pull-out simulation,the single-layer GO is pulled out of the 4-layer GO model GOS(II),and the interfacial shear strength between GO is calculated to be 465.35 MPa.By stretching and pulling out the molecular model of CSH/GO(1,2 and 4 layers GO respectively),the simulation results show that as the number of GO layers increases,the mechanical properties of the CSH/GO molecular model will increase At the same time,its interface shear strength(IFSS)will be improved.Among them,the interfacial shear strength of the C-S-H/GO model containing a single layer of GO is calculated to be 164.24 MPa.When the model contains four layers of GO,the IFSS is increased by about 28% compared with the model containing only a single layer of GO.Secondly,the 1-layer,2-layer,and 4-layer GO elastic modulus obtained by molecular dynamics simulation and the corresponding CSH/GO interface parameters are substituted into the finite element model,and the three-dimensional GO cement-based composite material is analyzed by finite element simulation.Three-phase and two-phase representative volume element(RVE)models are used for tensile and compression simulations,and the changes in the mechanical properties of composite materials are studied from the mesoscopic scale when GO appears multi-layer stacking.The simulation results show that the stacking of GO can weaken the strength of GO cement-based composites,especially its tensile mechanical properties.When the interface effect is not considered,the reduction can reach 22%.If the interface is considered as the interface between CSH and GO,the reduction can reach 28.6%.Stacking of GO will reduce the strength of the composite material.Finally,through uniaxial compression tests on the mechanical properties of GO modified cement paste and mortar,the effect of different GO content on the compressive properties of GO modified cement-based composites was studied from the perspective of macroscopic experiments.At the same time,the dispersant was changed.The amount and type of the dispersant were studied to study the influence of the dispersant on the compressive properties of GO modified cement-based composites.Through the uniaxial compression test,the results show that when 0.03wt% and 0.06wt% GO are added,the compressive performance of cement-based composites can be enhanced,while when the content of GO is 0.1wt%,the compressive resistance of the composites will be damaged.performance.The content of 0.06wt% GO has the best enhancement effect,which can increase the 14-day compressive strength of the pure mortar test block by 15.49% and the28-day compressive strength of the mortar test block by 13.16%.At the same time,the influence of the water reducing agent on the composite material is not negligible.It is found that the addition of polycarboxylic acid type superplasticizer(SP)will reduce the14-day compressive strength of the test block,but 0.03wt% and 0.06wt% of GO are added.All have grown since then.Compared with the control group after SP was added,the 14-day compressive strength increased by 58.51% when GO content was 0.06wt%.