Effect Of Electrical Field On Formation And Stability Of Ettringite In Cement-based Materials

Ettringite is a kind of sulphoaluminate mineral,which is an important product of cement hydration and the main product of sulfate attack.The composition and structure of ettringite and its changes due to the external environment play an important role in the performance of cement paste and concrete.With the research and application of electrical field in cement-based materials increasing,it is necessary and important to study the formation and stability of ettringite in cement-based materials under electrical field.In this paper,the methods of appearance change,temperature change,compressive strength,chemical analysis and X-ray diffraction analysis were used in the study of ettringite by cement hydration and sulfate attack respectively.Main contents of this paper included,under different electrical fields,different cement types,different dosage of gypsum,different sulfate attack conditions,how the formation of ettringite in cement-based materials change,how the stability of ettringite produced by hydration of cement or sulfate attack under electrical field.The test results are as follows:(1)The formation of early ettringite in cement-based materials was affect by electrical field and the distribution of ettringite was not uniform,but the amount of ettringite in the final sample was not very different from that of the non-electrical group.(2)The temperature changes caused by different voltage electrical field were different,the temperature of 30 V electrical field specimen were higher than water soak specimen about 1.9-3.5 °C,while the 60 V specimen were about 2.5-4.8 °C,the temperature changes caused by electrical field under this test condition was not enough to affect the change of the hydration products such as ettringite.However,the ion migration induced by electric field can affect the formation of early ettringite,and the higher the voltage,the effect was more obvious.(3)When different types of cement were used,the electrical field is not conducive to the early formation of ettringite in portland cement,meanwhile an electrical field can accelerate the early hydration of sulphate aluminate cement and the reaction of gypsum and aluminate cement,resulting theirs early ettringite slightly tall,but the continued action by electrical field can lead the reduction of ettringite caused by the ions migration in a specimen.(4)The formation of ettringite were more in specimens with higher gypsum dosage,however,the amount of ettringite in cement with 5% and 8% dosage of gypsum were rarely changed.An electrical field can make ion migration and affect the early formation of ettringite in portland cement with different dosage of gypsum.The amount of ettringite decreased slightly as the electrical field caused the ions to move out.(5)Under the different sulfate attack,ettringite formation rate was the fastest in sodium sulfate solution combined with electrical field,the generation of ettringite was the most.The sulfate attack were slower and less amount of ettringite were generated in other two kinds of sulfate solution,this was because itself concentration were lower and the impact of the existence of calcium ions.(6)Under the action of electrical field,the ettringite produced by hydration of portland cement was unstable and the limestone powder can cause ettringite was more easy to decompose,the fly ash can result a certain degree of reduce the decomposition of the ettringite,but the influence is limited with time.The ettringite produced by hydration of sulphae aluminate cement hydration was also unstable under electrical field.The calcium hydroxide solution can effectively inhibit the decomposition of ettringite before 120 d and gradually not work in later.(7)Under the action of electrical field,the ettringite produced by sulfate attack were unstable.In this stage,fly ash and other admixtures,as well as calcium hydroxide solution,the Inhibition of ion migration were very small.To conclude,the formation and stability of ettringite in different ways were certain affectd by electrical filed,and the influence were more obvious with the longer time under electrical filed.Fly ash and calcium hydroxide solution can inhibit the decomposition of ettringite in certain degree,but they were gradually not work in later.