Hyperbaric-oxygen accelerated corrosion test of iron in cement paste and mortar

A novel accelerated corrosion test method enhancing oxygen supply to simulate the corrosion of reinforcing steel in concrete has been proposed in this study. Oxygen reduction current density measured by means of potentiodynamic polarization test for a Fe sample embedded in cement paste or mortar in a saturated Ca(OH)₂ solution under ambient air decreased with an increase of the cover thickness and the current density was inversely proportional to the cover thickness from 1 mm to 10 mm, suggesting that diffusion limited oxygen reduction can be accelerated by making the reducing thickness below 10 mm. The novel strategy to enhance oxygen supply in the proposed method is to apply pressurized oxygen instead of ambient air using a newly developed hyperbaric oxygen accelerated chamber. In 0.5 MPa of oxygen Fe samples covered with 5 mm of mortar or cement paste showed oxygen reduction current density almost 25 times as high as that under the ambient air. The thickness of rust layer formed during 30day corrosion test of Fe samples covered with 5 mm of mortal or cement paste containing chloride ion in a saline solution under 0.5 MPa of oxygen was in good agreement with the increased oxygen reduction current density, indicative of acceleration of corrosion proportional to applied oxygen partial pressure. Furthermore, the characteristics of the rust formed under the pressured oxygen were similar to that of the rust formed under a practical service environment. Thus, the hyperbaric oxygen is beneficial and effective to validly accelerate the corrosion of reinforcing steel in concrete.