51314-4145-Electrochemical Behavior of the Prestressing Steel in Alkaline Electrolytes:Influence of Cement Type

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Product Number: 51314-4145-SG

ISBN: 4145 2014 CP

Author: Ioan PEPENAR

Publication Date: 2014

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The paper presents the results of research on the electrochemical behavior of prestressing steel in alkaline electrolytes with various types of cements by using potentiodynamic polarization technique.The research was performed on two types of high-strength steel used as tendons for prestressed concrete: cold-drawn steel with pearlitic microstructure and thermally treated (quenched and tempered) steel with martensitic microstructure. Six types of Portland cement recommended for use in prestressed concrete structures have been tested. The electrolyte solution consisted of an aqueous suspension of Portland cement with cement/water ratio of 1:10. The potentiodynamic curves of steel specimens in electrolyte solutions were traced in the potential range between -1000 mV and +1000 mV with a scan rate of 0.556mV/sec in order to obtain reproducible results and to determine all the characteristics of electrochemical behavior of prestressing steels. After each potentiodynamic polarization test the steel specimens were examined visually and microscopically.The shape of the anodic polarization curves is typical for the behaviour of a metal which passivates in alkaline media. From polarization curves shape was determined electrochemical parameter values of steels tested depending on the type of cement which varies between the following limits:- passivation potential: - 450…-335 mV (SCE);- O2 release potential: +620…+650 mV (SCE);- current density in passive state: 6…15 µA/cm2;- passivity zone: 975-1115 mV (SCE).The OPC potential and the pH of electrolyte solutions were also measured.The difference between the passivity characteristics values of the two types of tested prestressing steels is insignificant. The passivity characteristics values of steels immersed in aqueous suspensions of cement without admixtures are superior to those of steels immersed in aqueous suspensions of cement with admixtures.The potentiodynamic polarization method is a rapid selective and efficient method for the comparative study of the influence of cements additives and admixtures on electrochemical corrosion behaviour of different types of prestressing steels in concrete.