Experimental Study On The Transmission Of Water And Chloride Into Concrete

In the current era of broad applications of reinforcement concrete,concrete durability is an urgent issue to be solved.The migration of water and chloride has a significant impact on the problem of concrete durability.Chloride corrosion is the core of concrete durability research,to solve the problem our country has carried out a number of project researches.This research relies on the study of the Fundamental Research on Sustainability of Reinforced Concrete Structures Based on Mass Transport Mechanism(2015CB655105).The corrosion mechanism of water and chloride into the concrete are the key points.The details of this thesis are presented as following:(1)Specimens with different saturation and water-cement ratios were conducted for capillary adsorption and chloride diffusion.The capillary absorption coefficient and the content of chloride with different initial saturation and water-cement ratios are obtained.Then based on the formula of capillary absorption coefficient and Fick's second law,the capillary absorption coefficient and the chloride diffusion coefficient are calculated.The results show that the capillary absorption is linearly related to saturation and water-cement ratios,which increases with the rise of saturation,but indicates the reverse trend with increment of water-cement ratios.The chloride diffusion is the mainly mechanism for saturated concrete,and the diffusion coefficient changes expressively with the water-cement ratios and the diffusion time.(2)The temperature and relative humidity in the concrete of different depths were measured by using the temperature and humidity sensors for water-cement ratios of 0.2 and 0.5.The temperature and humidity of the concrete were measured at 70 ? during the drying and wetting.The results indicate that the temperature is affected slightly by the depth of embedded depth,but it is sensitive to the external environment.The inner relative humidity varies with the sensor embedded depth from the bottom of the concrete and the relative humidity decreases slightly during drying.The relative humidity in the process of water absorption changes slowly near the bottom zone.The water-cement ratios have a significant effect on the drying and wetting process of concrete samples.And it can be seen that the water-cement ratio of 0.5 is obviously faster than the water-cement ratio of 0.2 in the drying process and the wetting process.And the mass loss of water per unit area was found to be linearly related to the square root of time in the drying process.(3)The adsorption-desorption of specimens was tested to study the water migration in the concrete by using saturated salt solution to control temperature and relative humidity of the chamber.The isothermal adsorption desorption curve and water characteristic curve of the concrete were obtained.It was found that the adsorption and the desorption curve had obvious hysteresis,and the adsorption curve was above the desorption curve.