Water And Chloride Ion Transmission Behavior And Life Prediction Of Aeolian Sand Concrete

With the vigorous development of China’s construction market and the advancement of infrastructure in the belt and road initiative,the demand for construction raw materials is increasing day by day.If aeolian sand,as a natural resource "waste",can replace ordinary river sand in concrete,it can reduce the collection and utilization of river sand and the project cost,and be conducive to environmental protection and improve the environment,with remarkable social and economic benefits.Based on the comprehensive consideration of regional characteristics,this paper studied the durability of aeolian sand concrete with chlorine salt erosion and wet-dry cycles environmental effects,and analyzed the transmission law of moisture and chloride ions in it,providing theoretical support for the practical use of aeolian sand concrete.In the experiment,aeolian sand was used to replace ordinary river sand to prepare aeolian sand concrete.The replacement rates of five aeolian sand were 0%,25%,50%,75% and 100%respectively.The influence of different aeolian sand content on the capillary absorption of concrete was analyzed,and with the help of microscopic nuclear magnetic resonance to analyze its pore structure,the quantitative relationship model between micro and macro was established.At the same time,five types of aeolian sand concrete were subjected to dry-wet cycle tests in a chloride environment.The internal structures of the five kinds of aeolian sand concrete before and after the dry-wet cycle were analyzed by means of X-ray diffraction analysis,field emission environment scanning electron microscope,nuclear magnetic resonance and other microscopic means,so as to explore the law of chloride ion transmission and the characteristics of pore structure change.The main research conclusions are as follows:Adding a proper amount of aeolian sand to concrete can densify the pore structure,improve its compressive strength and slump,and reach the optimum when the amount of aeolian sand is 25%,increasing by 6.5% and 7.7% respectively.When the amount of aeolian sand is 100%,the compressive strength is the smallest.The compressive strength of the five groups of aeolian sand concrete meets the design requirements.In the experimental study of the water and chloride ion transmission behavior in aeolian sand concrete: the curve of capillary absorption of concrete with square root of time increased linearly in the early stage,and then gradually tended to be horizontal due to the weight of solution and the friction of pore wall;Chlorine salt absorbing solution with higher concentration(10% NaCl solution)is easy to produce salt crystal and ion blockage,which leads to the decrease of capillary absorption coefficient;the water and chloride ion transmission depth in aeolian sand concrete is linear relationship.When the water transmission is stable,chloride ions are still transported into concrete due to diffusion;the proportion of aeolian sand concrete capillary pores and porosity can better characterize the change law of the capillary absorption coefficient,and the binary function relationship model of the capillary absorption coefficient with its change is established.The transmission law of chloride ions in aeolian sand concrete under the action of dry-wet cycle is as follows: As the dry-wet cycle progresses,the content of free chloride ions in the concrete gradually increases.Concrete with aeolian sand content of 25% can better block the intrusion of chloride ions;the binding capacity of chloride ion shows good linear binding,and with the increase of aeolian sand content,the binding capacity first increases and then decreases;Microscopic analysis shows that representative Friedel’s salt generated by wet-dry cycle is beneficial to compact concrete internal structure,and 100% content of aeolian sand is beneficial to weaken concrete damage caused by wet-dry cycle in early stage,while it accelerates damage in later stage.The functional relationship model between the chloride ion diffusion coefficient D of aeolian sand concrete and the amount of aeolian sand is established,and the value of the chloride ion diffusion coefficient under the action of a specific amount of aeolian sand is obtained.;Through Monte Carlo statistical simulation and Weibull distribution,the service life values of aeolian sand concrete with different failure probabilities are obtained.