Corrosion Behavior of Prestressing Steel in a Solution of 20％ Ammonium Thiocyanate

Abstract

High-strength steels or PC steel products are used for pre-stressed concrete structures. Testing of PC steel products in terms of hydrogen embrittlement is specified in the FIP Report, and the test method adopted in ISO 15630 is well known. This test is called the FIP test, whereby a constant load is applied to PC steel in a 20％, 50℃ ammonium thiocyanate solution. An investigation was carried out on the corrosion behavior of 1,400 MPa class PC steel products in a FIP testing environment. Under this testing environment, a cathodic reaction associated with oxygen consumption and hydrogen generation was identified from the initial stage of dipping, and corrosive products mainly consisting of ferric sulfide were formed on the surface of a specimen detected in the test pieces. From changes in the amount of gas associated with the reaction, it is understood that, together with this corrosion reaction, there also occurred a reaction involving 1 mol of hydrogen generation or 0.5 mol of oxygen consumption for 1 mol dissolution of iron. It is also assumed that the reaction involving hydrogen generation was a cathodic reaction associated with the decomposition of SCN^－.