Quick Visual Characterization And Quantitative Analysis Of The Moisture Transmission Process Of Cement-based Materials With Cracks

The durability and service life of concrete structures depend to a large extent on the process of fluids passing through the cementitious material.These liquids may contain corrosive substances that cause deterioration of the concrete matrix and corrosion of the reinforcing bars,which can prevent the building from reaching its normal useful life.In most cases,the main mechanism by which water enters the gelling material is capillary absorption,especially when cracks are present.Advances in neutron,nuclear magnetic resonance and x-ray imaging technologies have greatly improved our experimental ability to observe fracture flow in various saturated porous media.As a result,researchers are now able to routinely quantify the distribution and movement of water over a wide range of natural and engineering materials at the spatial and temporal resolution associated with fracture flows.To be able to predict the durability of cracked concrete structures,it is necessary to understand the distribution of water in cracked cementitious materials.This paper mainly uses X-ray tomography technology(X-ray Tomography Technique,XCT for short)to visually track and characterize the transport process and law of water in the cement base with cracks.(1)Capillary water absorption test and XCT test are performed using cesium chloride solution instead of pure water as CT image enhancer to achieve in-situ and visual characterization of the dynamic transmission process of water in cement-based materials.Breakthrough XCT technology cannot directly track the purity of water in cement.Limitations of water migration.After many experiments,it was found that when the cesium chloride solution with a mass fraction of 10% can obtain a CT image with obvious contrast,it can clearly define the water-absorbed and non-absorbed areas in the pulp.(2)Using the relevant image correction theory,the non-uniformity of the X-ray field is corrected,and the moisture content distribution is quantified.A method for field non-uniformity correction and water content calibration is proposed.The distribution law of cesium ion concentration in water-free cement-based samples with a crack of 0.5 ater-cement ratio after 2 hours of capillary water absorption by measuring the actual water absorption depth of the sample and the potentiometric titration method to determine the distribution law of the cesium ion concentration with water absorption depth.The correction and gray-scale calibration methods are effective for tracking the moisture transmission process in the cement base.In addition,the XCT technique was used to visually monitor in situ and describe the 2D evolution process of water transport in five samples with different fracture widths(fracture widths of 0.02,0.04,0.1,0.2,and 0.6,respectively).(3)Weighing method was used to study the water transmission in cement.It was found that under the action of capillary adsorption,as the water absorption time increased,the capillary water absorption process of the sample showed a rapid increase in water absorption in the early stage and a gradual slowness in the later stage.At the same time,the capillary water absorption per unit area of ??five samples with different crack widths shows a linear relationship with the fourth root of time,and the slope of the fitted curve is the capillary water absorption S.The larger the crack width,the greater the capillary water absorption and the greater the water absorption.(4)Using XCT technology and cleave measurement to study the law of capillary water absorption depth in cracked cement substrates over time,it was found that under capillary adsorption,as the water absorption time prolonged,the capillary water absorption process of the sample showed The process of rapid increase in water absorption in the early stage and gradually slow in the later stage.At the same time,the capillary water absorption depth of five different crack widths has a linear relationship with the square root of time,which conforms to the Locas-Washburn equation,and the slope of the fitted curve is the capillary coefficient k.The larger the water-cement ratio,the deeper the capillary water absorption depth and the larger the capillary coefficient.(5)The capillary water absorption coefficient and capillary coefficient of the test block with cracks under capillary water absorption have a good linear relationship,which is consistent with the conclusion obtained by Han?i?et al.Using neutron imaging technology.