Experimental Investigation On The Evolution Of Pore Structure And Chloride Diffusion For Cement Mortars

In coastal environments or areas with high chloride content,the greatest threat to the durability of concrete is the erosion of chloride ions.High temperature and humidity changes can affect the chloride ion transport properties in concrete.The chloride ion transport in concrete is very complex,and the current theory of temperature and humidity affecting chloride ion transport properties is not well developed.As chloride ions in concrete can only be transported through the internal pore space,so the pore structure plays an important role in the transport of chloride ions.For the process of chloride salt erosion of concrete,research of the effect of temperature and humidity changes on the pore structure and chloride ion diffusion performance is the basis for concrete analysis of the actual chloride salt leading to durability problems,and is also of great engineering importance.In this paper,the effects of temperature and humidity variations on the pore structure and chloride ion diffusion properties of mortar are investigated.The pore structures of mortars in wet and dry environments are completely different.Since chloride ions can only be transported in the wet pore space,this paper uses the low-field magnetic resonance technique to accurately test the pore structure of mortars in the wet state.In order to better simulate the chloride ion transport process under natural environment,the natural diffusion method is used to test the chloride ion diffusion performance in this paper.The specific research content is as follows,firstly,to study the effect of high temperature on pore structure and chloride ion diffusion performance,introduce the change of mortar pore structure and chloride ion diffusion performance before and after high temperature,analyze the effect of temperature on pore structure,and analyze the reason for the change of chloride ion diffusion performance caused by high temperature in combination with the change of pore structure.Secondly,to study the effect of drying action on pore structure and chloride ion diffusion performance,two different drying actions,room temperature drying and high temperature drying,were chosen to compare the pore structure changes and chloride ion diffusion performance results of mortar after re-saturation by the action of different drying conditions,to analyze the effect of different drying actions on pore structure and the effect of drying action on chloride ion diffusion performance.Finally,all the pore structure parameters and chloride ion diffusion performance data were combined in an attempt to quantitatively link the pore structure and chloride ion diffusion performance.The results showed that the chloride diffusion performance of mortar after heating water bath was higher than that of mortar without heating water bath,which was attributed to the coarsening of the internal pore structure of mortar by high-temperature water bath.After the mortar was re-saturated with water by different drying effects,its internal pore structure was coarsened and the chloride diffusion performance was higher.Porosity and curvature are important parameters linking chloride ion diffusion performance and pore structure,and the logarithmic mean pore size within the gel is considered as curvature,which has a good linear relationship with the product of porosity and chloride ion diffusion coefficient.