Materials Transactions Online

Materials Transactions, Vol.59 No.06 (2018) pp.927-934
© 2018 The Japan Institute of Metals and Materials

Hyperbaric-Oxygen Accelerated Corrosion Test for Iron in Cement Paste and Mortar

Kotaro Doi1, Sachiko Hiromoto2 and Eiji Akiyama3

1International Center for Young Scientists (ICYS), National Institute for Materials Science, Tsukuba 305-0047, Japan
2Research Center for Structural Materials, National Institute for Materials Science, Tsukuba 305-0047, Japan
3Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

A novel accelerated corrosion test method which enhances oxygen supply has been proposed for reinforcing steel in concrete in this study. Oxygen reduction current density (ORCD) was measured by means of potentiodynamic polarization test for an iron specimen embedded in cement paste or mortar in a saturated Ca(OH)2 solution in ambient air. The ORCD decreased with an increase in cover thickness and the current density was reciprocally proportional to the cover thickness from 1 mm to 10 mm, suggesting that diffusion limited oxygen reduction can be accelerated by reducing the cover thickness below 10 mm. The oxygen supply to iron surface in cement paste or mortar was enhanced by pressurized oxygen gas using a newly developed hyperbaric-oxygen accelerated corrosion test container. Iron specimens with 5 mm cement paste and mortar covers showed almost 25 times higher ORCD in 0.5 MPa oxygen gas than that in ambient air, respectively. The iron specimens covered with 5 mm of cement paste or mortar containing chloride ion were immersed in a saline solution and exposed to 0.5 MPa oxygen gas in the container for 30 days. The thickness of the rust layer formed for 30-days was in good agreement with that estimated from the ORCD obtained in 0.5 MPa oxygen gas, indicating that the corrosion was accelerated in proportion to the oxygen (partial) pressure. Furthermore, the rust formed in pressurized oxygen gas showed similar characteristics to that formed in a practical service environment. Thus, the hyperbaric-oxygen is beneficial and effective to validly accelerate the corrosion of reinforcing steel in concrete.

[doi:10.2320/matertrans.M2018029]

(Received 2018/01/26; Accepted 2018/03/12; Published 2018/05/25)

Keywords: corrosion, reinforcing steel, concrete, rust, hyperbaric-oxygen, accelerated corrosion test

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