Effect Of Silane On Unsaturated Transmission Of Cement-based Materials Based On Molecular Dynamics Theory

As an ideal concrete waterproofing material,silane can form a layer of hydrophobic layer on the concrete surface by various methods such as impregnation and spraying.It can improve the waterproof,anti-fouling and anti-corrosion ability of concrete.In recent years,researchers have studied the reaction and waterproof mechanism of silane on concrete surfaces by modern techniques such as electron microscopy,comprehensive thermal analysis,infrared spectroscopy,X-ray diffraction,and neutron imaging.It is generally considered that silane is bonded to the surface of the gel pores of the concrete surface layer by a reaction such as dehydration or condensation.A water-repellent layer is formed using its protective group(carbon chain).It can inhibit the external water and the erosive ions(Cl-,SO42-,etc.)dissolved therein to diffuse into the concrete to achieve the purpose of anti-corrosion.However,at a deeper microscopic scale,it is currently not clear how silane molecules prevent the diffusion of moisture in C-S-H gels.In order to understand the silane protection mechanism from the microscopic scale.Therefore,based on molecular dynamics,this paper simulates the effects of different concentrations and different types of silane on water and ion transport in concrete gel channels.The main hydration product of concrete is C-S-H gel,so the upper gel channel of the unsaturated transport model is a 2-layer tobermorite structure,and the bottom solution is selected according to the simulation.Silanes are selected for the more common types tested.The hydrolysis reaction occurs because the silane enters the pores.In order to be more realistic,silanol was selected for simulation to construct a reasonable unsaturated transport model.The main research contents are as follows:(1)Based on molecular dynamics,we simulated the transport of water molecules into the gel pores with different concentrations of silane.By analyzing the structure of water molecules and silanol molecules,interactions with the interface and kinetics,it can be found that as the number of silanol molecules increases,the probability of contact with the interface increases during the process of entering the gel pores.It is easier to form a hydrophobic film layer at the interface by electrostatic force.(2)Compare the different placement of silanol molecules.We have found that when silanol molecules are placed directly into water to simulate the transport of silanol molecules into the pores of the gel,their inhibition of water molecule transport is less stable than the arrangement of silanol molecules at the interface of the gel pores.The first placement method is because the silanol molecules are far away from the interface,and the inter-molecular interaction with the interface is weak,mainly forming clusters to inhibit the transport of water molecules;in the second placement,it is easier to form a hydrophobic membrane layer.Therefore,the suppression effect is more obvious.(3)We selected different kinds of silane molecules and studied the effects of different silane molecules on inhibiting the transport of water molecules in the C-S-H gel channel.The materials of methyltriethoxysilane,vinyltriethoxysilane,isobutyltriethoxysilane and octyltriethoxysilane were mainly selected for comparison.Firstly,in the macro contact angle test and the capillary water absorption test,it was found that the concrete block treated with octyltriethoxysilane had a contact angle of 132° and a water absorption coefficient of about 79%,which can effectively inhibit water molecules.The same test results were obtained by simulating the four silanol molecules.Since octyltriethoxysilane can not only form a hydrophobic film at the interface by intermolecular force connection,and its relative molecular mass is large,the carbon chain is long and relatively stable.Therefore,its protective effect is the best.(4)Three kinds of materials,such as methyltriethoxysilane,vinyltriethoxysilane and isobutyltriethoxysilane were selected for rapid chloride ion penetration test.Compared with the blank group,it was found to be effective in reducing chloride ion erosion.The simulation results are consistent with the experimental results.Chloride ions dissolve in water and enter the concrete.Isobutyl triethoxysilane slows the transport of chloride ions into the pores while inhibiting the transport of water molecules.At the same time,isobutyltriethoxysilane forms a cluster,blocks the pores,and encapsulates the ions,causing the ion transport to slow down.