Study On The Damage And Ions Diffusion Of Concrete In The Chloride-sulfate Environment

In some environments, just like marine,saline fields and underground, there oftenexist many different corrosive ions such as Cl-and SO42-, instead of only one kind ofion. So the structures made of concretes are often subject to common corrosion ofdifferent corrosive ions. Moreover, it is considered that concrete structures oftenfunction under loads, the harmful ions and stresses might have lots of coupling effectson the structures. Definitively, these coupling effects will lead to composite damage ofthe concrete and influence the diffusion of the ions.Basically, in this paper, the composite damage and damage mechanism ofconcrete in coexistent environment of SO42-and Cl-is studied. Finally, the diffusion ofharmful ions in the concrete is also analysed.The main achievements are concluded as follows：1． Compared with SO42-corrosion and Cl-corrosion, the mechanical propertiesof concrete on SO42--Cl-coinstantaneous corrosion are analysed by macroscopic test.The result indicates that: in the SO42--Cl-coexistent environment, Cl-will benefit thestrength of concrete in the early corrosive period, and the strength will increase to beaccompanied by the increase of Cl-concentration.2．The microscopic method based on XRD is used, in order to analyse theproducts caused by Cl-corrosion, SO42-corrosion, SO42--Cl-coinstantaneouscorrosion.Finally, the explaination of the change in macroscopic mechanicalproperties is given.3．Experiment of ions diffusion within the concretes is conducted in this paper.The research indicates that in the early period of corrosion(within180days),thecoupling effect delays the ions diffusion of both SO42-and Cl-.4．Based on the Fick’s second law, considering the loss of ions(SO42-, Cl-)reacting with some concrete hydration products,a two-dimensional diffusion-reactionmodel for SO42-and Cl-in coexistent environment is respectively deduced. Themodels are solved by finite difference method, and a solving program is set up though Matlab.Finally,the models are authenticated and modified by the results of diffusionexperiment.The research indicates that the values calculated by thediffusion—reaction models and the results got from the diffusion experiment areconsistent.5. The corrosion conditions with stress and harmful ions, such as SO42-and Cl-,are designed for researching the composite damages of concrete in these conditions bymacroscopic test. The results of this research indicate that flexural-tensile stress willaccelerate the degrading rate of strength, and the stress-level is higher, the strength ofconcrete will degrade more rapidly.