Research On Simulation Of Water Transport In Nano-scale Pores Of Cement-based Materials

As we all know,concrete is widely used in water conservancy and construction projects.Under normal conditions,concrete has superior durability,but under special conditions,its frost resistance,impermeability and erosion resistance will decrease and cause easy damage.It is a critical issue that has not been overcome in engineering construction in our country,so this article will discuss the damage mechanism of cement concrete in water environment.The main hydration product of cement is C-S-H,which determines the strength of cement concrete to a certain extent.Almost all the degradation reactions of concrete come from the erosion of water and ions.At the macro level,the theoretical studies and experiments on the transmission of water and ions have been more detailed.There are few studies on the microscopic view,but in recent years,it has received more and more attention and has become a popular angle in concrete research.Therefore,in this article,we choose to explore the characteristics and reactions between water molecules and ions from a microscopic point of view.Based on the theory of molecular dynamics,we explore the transfer of water molecules and ions in the C-S-H gel nanopores on cement concrete.The impact of durability and sustainability.In the establishment of the model,the unsaturated transmission model is composed of two parts: the upper layer of hydrated calcium silicate nanochannels,and the lower part is used to simulate the saturated sodium chloride solution of the erosion solution in the real environment.This is a non-saturation that is closer to reality.The saturated transmission model is constructed.Previous researchers have discussed the transport of water and ions between parallel C-S-H gel nanopores,but there are few mentions of other nonparallel variable cross-section nanopores.Therefore,we analyzed the structural characteristics and molecular dynamics characteristics of the transport process by changing the distance between the C-S-H gel nanopores,that is,the pore size,and the offset angle of the middle section of the C-S-H.Explore the effects of different shapes and sizes of gel pores on the transport of water and ions,and explore the mechanism and characteristics of ion erosion.For the two types of models,the main research contents are as follows:For unsaturated models,we have compared and studied the following two types: ⅠModels with pore diameters of 2.5nm and 3.5nm respectively Ⅱ C-S-H gel nanometers with initial pore diameter of 3.5nm and offset angles of 0° and 10° Transmission characteristics of water and ions in the pores.During the transmission process,we can find the following rules.First,the transmission of each model is affected by capillary action.During the transmission process,the front interface gradually assumes the shape of the meniscus.This is very consistent with the classic LW capillary absorption theoretical model theory,but less than The intrusion angle of the liquid surface of 90° also confirmed the hydrophilic properties of the CS-H gel.Based on the distribution curve of atomic and ionic strength,the maximum peak of the atomic strength near the pore interface can also confirm the hydrophilic properties of C-SH The strength curve of sodium ions is closer to the gel pore interface than the intensity curve of chloride ions,which is due to C-S-H silicate gel pores are attractive to cations.The transmission speed and diffusion rate of water molecules and ions are also different under different conditions.By summarizing the penetration depth curve of water molecules and ions and the MSD,the following conclusions are drawn: in the 3.5nm model,the transmission speed of water and ions in the channel is relatively fast,and the difference between the transmission speeds is small,while in the 2.5nm model,The transmission speed of water molecules and ions is obviously slowed down,and the transmission speed of water molecules is obviously greater than that of chloride ions and sodium ions.This trend becomes more and more obvious in the 1.5nm channel.In the 10° migration model,the transmission speed of water and ions is slow,and the transmission speed of water molecules is greater than that of chloride ions and sodium ions.This shows that when the hydrated calcium silicate gel nanochannel shape occurs When it changes,the transmission performance of erosion ions and water molecules will also change.This law is helpful to further explore the causes of ion erosion in cement concrete and reveal the microscopic mechanism of water molecules and ions transmission between them.Thereby it is connected with the macroscopic,and promotes the performance improvement of cement concrete.