Molecular Dynamics Study On Hydrophobic And Mechanical Propertie Of Silane/Go Modified Sulfoaluminate Cement-Based Materials

Sulfoaluminate cement is widely used in repair engineering because of its fast setting speed,high early strength and slight expansion of hydration.However,as a complex porous material,sulfoaluminate cement-based repair material is vulnerable to erosion media in the marine environment,which would lead to the destruction of the internal microstructure of the repair materials,rapid degradation of cementitious force,and increase of reinforcement corrosion rate,resulting in a general decline in service performance of the repair materials.Therefore,it is of great engineering significance to explore effective methods to improve the hydrophobic property of sulfoaluminate cement-based repair material,so as to enhance the strength and durability of the repair project.As a kind of permeable protective material,silane can form a hydrophobic film on the surface of concrete to resist the invasion of corrosive ions.However,silane is unstable and volatile,and its water resistance would affect the hydration reaction of cement,which will lead to the weakening of the strength microstructure of cement-based materials.Based on this,GO modified isobutyltriethoxysilane（IBTS/GO）emulsion is prepared in this paper to give full play to the excellent permeability and water resistance of silane,as well as the effect of GO on the microstructural improvement of cement-based materials,and to explore its influence on the waterproof and mechanical properties of sulfoaluminate cement-based materials.Molecular dynamics simulation is used to explore the modification mechanism of IBTS/GO modified sulfoaluminate cement-based materials.The main conclusions are as follows:（1）The IBTS/GO emulsion can effectively improve the wetting property of the interface of sulfoaluminate cement-based materials,and the improvement effect is stronger than that of the IBTS emulsion.Contact angle test results show that the hydrophobic effect of the IBTS/GO coating is the best,followed by the IBTS coating.Interface wetting simulation shows that the AFt substrate has hydrophilicity,and water molecules in the droplets will penetrate the AFt interface and exchange with the bound water in AFt.The presence of the IBTS coating can effectively limit the invasion of water molecules and hinder the wetting behavior of droplets,but the droplet will still break through the limitation of the IBTS coating and invade the substrate.The IBTS/GO coating relies on the blocking effect of GO and the adsorption effect on IBTS to limit the droplet on the surface of the IBTS/GO composite system,further limiting the movement of the droplets and keeping droplet in a spherical shape.（2）The IBTS/GO emulsion has a better protective effect on water transport than the IBTS emulsion.The experiment of mass water absorption rate shows that the capillary water absorption rate and coefficient of the AFt substrate coated with IBTS/GO emulsion are significantly lower than those coated with IBTS emulsion.The pore transport simulation shows that IBTS,GO and AFt substrate interact with each other at the interface through Ca-O ionic bonds and hydrogen bonds.The form of IBTS-AFt interface interaction during the water transport process is easy to be destroyed,and IBTS is easy to desorb and transport in the pores with the moisture in the solution.However,GO can capture the desorbed IBTS,forming a more stable"GO-IBTS-H₂O-IBTS-GO"network,further hindering the intrusion of water.The oxidation process of GO and the pore size affect the transport of water in the nanochannels.The higher the degree of GO oxidation and the larger the transport channel,the faster the water transport rate.（3）GO modification can improve the mechanical properties of IBTS/sulfoaluminate cement-based material system.The mechanical strength test shows that the flexural and compressive strength of the IBTS/GO system is greater than that of the IBTS system.Mechanical performance simulation found that due to the double-sided structure and large specific surface area of GO,it improves the interaction strength and stability between IBTS-GO and AFt interface.During the dynamic tensile stage,the interface rupture between IBTS,IBTS-GO,and AFt is due to the breakage of Ca-O ionic bonds and hydrogen bonds.The force required for the interface rupture of both systems is positively correlated with the stretching velocity.The IBTS-GO system requires greater potential energy to transition from a stable combined state to an interface separation state.The bonding performance of the interface of IBTS-GO is stronger than that of IBTS.