Hydrogen embrittlement of prestressing steel

Despite new bridges appear every day ; the world bridges heritage includes a lot of ageing structures. One of the major phenomena which can be a potential source of disasters is the corrosion of metallic elements. Typically, the affected metallic parts in prestressing technology are cables. Although they are normally protected by a cement grout, the strands can suffer from general corrosion but also from a more harmful form as stress corrosion cracking (SCC). The main objective of this experimental study is to characterize with different methods (NDT methods, mechanical tests, metallographic observations) the SCC behaviour of prestressing steels. Damage mechanisms have been simulated with accelerated corrosion tests on laboratory specimen. The first step of the experimental work consists in the characterization of electrochemical behaviour of cables. The influence of temperature and ionic species concentration in the corrosion solution has notably been studied. The second step concerns the monitoring of damage evolution caused by SCC to metallic strands. A corrosive solution of ammonium thiocyanate (NH4SCN) has been used. The specimens have been monitored by acoustic emission (AE) technique during whole stress corrosion tests until failure. The use of standard AE parameters can allows us to discriminate different damage stages. During these different stages, some tests were interrupted to correlate damage evolution and AE activity. This degradation has been studied by mechanical tests (tension tests) and metallographic observations