Research On The Durability And Service Life Prediction Of Concrete In Composite Salt Solution

The problem of concrete durability is one of the important problem in the design of concrete structures, the lack of concrete durability will lead to the decline of the normal service capacity in the whole concrete structure. And It is the environmental water problems that the concrete exposed to sulfate, and the sulfate has a great damage to the concrete. There is a high concentration of sulphate, magnesium salt, chlorine salt in the western region of China and reduce the working performance of the local concrete. Therefore, It is important significance that study on failure law of the concrete in sulfate solution and improve the practical ability of the local concrete.Firstly through the experiment study on the concrete under the action of single factor (sulfate solution), double factor (magnesium sulfate solution), the three factors (magnesium sulfate-chloride solution) of concrete damage and pore connectivity changes of concrete in different corrosion environment. Secondly through experimental analysis diffusion law of the sulfate in the concrete, and the diffusion coefficient of sulfate in concrete is influenced by the external environment, and a modified model was established by consider the influence of the external environment on the diffusion coefficient of sulfate. Finally, based on the combination of theory and experiment, the life prediction model of concrete based on solid phase volume change theory is established.The change of dynamic elastic modulus concrete in single factor (sulfate solution), double factor (magnesium sulfate solution), the three factors (magnesium sulfate-chloride solution) s showed first slowly rise, with the increase of erosion time and then decreased, then increased, the erosion process appear showed wavy changes, the damage rate is increased with the increasing of the solution concentration and water cement ratio, in the early days of erosion inhibiting sulfate erosion and In the early stage of corrosion, the magnesium ion inhibited the corrosion of sulfate, and in the later stage of the erosion, the magnesium ion promoted the corrosion of sulfate to concrete; Chloride ions hinder sulfate attack concrete. In the high concentration of sulfate environment on the surface of the concrete damage is mainly gypsum results and inside the concrete is the results of interaction of gypsum and Ettringite. the concrete In magnesium sulfate solution in addition to suffer ettringite and gypsum material expansion failure and also suffer from Mg2+ chemical damage, the erosion process is a chemical and physical process; The damage of the concrete in the chloride and magnesium sulfate composite solution is predominated by gypsum failure, ettringite damage secondary injury process.The connected porosity change of concrete in salt solution solution is first decreased and then increased, change rate of connect porosity is increased with the increase of the concentration of sulfate decreases with the increase of the concentration of chloride ion, but magnesium ion in the early days of erosion connected porosity variation rate decreases with the increase of the concentration of magnesium ion, in the subsequent erosion increases with the concentration of magnesium ions increases.The concentration of sulfate in concrete is decreased with the increase of the depth of corrosion, and in the same layer of concrete shows the time accumulation, sulfate concentrations in concrete at the same depth and same erosion time is increases gradually with increase of water cement ratio, increases gradually with increase of the concentration of sulfate, with increasing chloride ion concentration decreased, and magnesium ions still inhibit the diffusion of sulfate in the initial erosion, erosion of the anaphase promoting the diffusion of sulfate and strength with the increase in the concentration of magnesium ion and enhanced. The diffusion of sulfate inhibited by the presence of chloride ions in concrete, improve the ability of concrete to resist the chloride erosion.Sulfate diffusion coefficient in concrete in is decreased with the increase of erosion time and increased gradually with the increase of water cement ratio and concentration of sulfuric acid root, with the increase of the concentration of chloride ion decreased, and the role of magnesium ion and macroscopic phenomena of the same, in the pre reduced expansion of sulfate diffusion coefficient, In the later stage, the diffusion coefficient of sulfate is increased by the Mg2+.