Hydrogen-embrittlement phenomena in post-tensioned cables of prestressed concrete bridges

The present work shows the results of a wide experimental test campaign on prestressing steel strands extracted from a prestressed-concrete bridge with post-tensioning system located in Northern Italy and affected by combined Hydrogen embrittlement and stress-corrosion phenomena. The prestressing steel cables were totally replaced due to the high deterioration detected during construction; air, humidity, and water coming from the injection nozzles not perfectly sealed, when cables were already under tension but before the completion of grouting operations led to Hydrogen embrittlement phenomena of the steel strands, with a rapid degradation of the mechanical performance and the drop of the deformation capacity. The modification of the failure modality was observed, with lots of strands showing the progressive breakage of single wires instead of the typical birdcage collapse. Tensile tests on more than 500 strands extracted from about 30 different cables in different positions, together with X-ray tomographies and micro-structural investigations on a reduced set of specimens were performed; results are presented and deeply discussed. Aim of the paper is highlighting the effects of Hembrittlement on prestressing products, the strong impact on the degradation of mechanical performance and the possible negative consequences on the structural behaviour.