An Electrical Field Accelerate The Behavior And Mechanism Of The Thaumasite Form Of Sulfate Attack In Cement Based Materials

The Thaumasite form of sulfate attack?TSA?of cement based materials is related to the sulfate and carbonate.This kind of sulfate attack will directly declassification the C-S-H gel to the grey pulp.In resent years,the limestone powder was used widely in the cement and concrete.The content of limestone powder in the cement and concrete had achieved 40%that was a huge potential threat for TSA of cement based materials.There was no a test method for testing rapidly the TSA of cement based material.The sulfate full immersion in a low temperature was the most used method to test the TSA that still needed at least 1 year.The above tests were not useful in the laboratory and engineering field for rapid test.The electrical field had been widely used to accelerate the migration of ions.Hence,the electrical field was used to accelerate the TSA of cement based materials in this paper.The degradation mechniasm and degradation process were studied,the main conclusions of this paper were shown as follow:?1?The TSA degradation behavior of the electrical field cathode Na₂SO₄solution-anode MgSO₄ solution,the Na₂SO₄ full immersion and the MgSO₄ full immersion was studied by the appearance change grade,fourier transformed infrared spectroscopy?FTIR?,Raman spectrum and x-ray diffraction?XRD?.These results indicated that the electrical field can accelerate the TSA and not change the degradation behavior and the acceleration rate was 4⁶ times than the full immersion.?2?The function of the electrical field on the sample was studied by the cathode water-anode water,cathode Ca?OH?₂ solution-anode Ca?OH?₂ solution and Ca?OH?₂&Na2SO4 solution-anode Ca?OH?2&Na2SO4 solution.These results indicated that the electrical field almost no influence on the hydration,pH and the content of Ca of the sample when there was no corrosion medium.The function of the electrical field is accelerating the corrosion medium into the sample lead to the acceleration of degradation.?3?The TSA degradation mechanism of the electrical field cathode Na₂SO₄solution-anode MgSO₄ solution,the Na₂SO₄ full immersion and the MgSO₄ full immersion was studied by the ions concentration distribution.The results indicated that there are the same degradation mechanism.The ettringite and gypsum was formed at first,then the thaumasite was formed by the ettringite,after that,the thaumasite was formed by the direct method that sulfate and carbonate react with the C-S-H gel.?4?Compared the research results,the degradation boundary conditions and the degradation model was presented:the pH and the Ca/S need to be meet the following conditions:10.60<pH<11.75,4.00<Ca/S<6.35.And,the degradation was divided into 3 stage,there were respective features and boundary conditions in these stages.?5?The influence factors of the TSA in the environment were studied by the appearance change grade,FTIR,Raman spectrum and XRD.The results indicated that the degradation of TSA was the most serious when the electrical field is a 30V-20s pulse electrical field,the cathode solution is Na₂SO₄ solution,the anode solution is MgSO₄ solution,and the test temperature is 5?.The results indicated that the electrical field can accelerate obviously the TSA degradation process,and the acceleration of the electrical field didn't change the degradation process and degradation mechanism compared with the full immersion.The effect of the acceleration of electrical field is making more corrosion medium into the sample.