Service life of hot-dip galvanised reinforcement bars in carbonated and chloride-contaminated concrete

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Doctoral thesis (monograph)
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Date

2009

Department

Rakenne- ja rakennustuotantotekniikan laitos

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Language

en

Pages

Verkkokirja (6235 KB, 177 s.)

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TKK structural engineering and building technology dissertations, 5

Abstract

The dissertation presents the work studying the factors influencing on the service life of hot-dip galvanised reinforcement bars. The experimental part of the study consisted of accelerated corrosion tests among others. The comparison of the measured crack width of concrete with the rate of corrosion values, and also with other measured values such as the corrosion potential, the resistivity of concrete, and the mechanical properties of the steel indicated no correlation irrespective of the duration of the exposure or type of aggressive liquid. The rate of corrosion decreased as a function of exposure time. This was not dependent on the water-to-cement ratio of concrete. Three probable corrosion mechanisms are determined for hot-dip galvanised reinforcement bars in cracked concrete, based on long-term durability tests and other studies. The first mechanism consists of a local dissolution of the eta (η) and zeta (ζ) phases of the zinc layer. In the second mechanism, as a result of the non-uniformity of the zinc coating, local dissolution of the eta (η) and zeta (ζ) phases, together with longitudinal and perpendicular cracking in the zinc layer, may lead to the local separation of the zinc layer. In the third mechanism, as a result of the non-uniformity of the zinc coating, full dissolution of eta (η) phase and partial dissolution of the zeta (ζ) phase, together with longitudinal and perpendicular cracking in the ferrite, may lead to the local separation of the zinc layer and the ferrite. The effects of different reinforcing steels on the service life of outdoor concrete structures were estimated through calculations. A stochastic method based on the probability of damage, Monte Carlo simulation, and reliability and sensitivity analyses were also used. In carbonated intact and cracked concrete the use of hot-dip galvanised reinforcement bars could double the service life compared with the use of ordinary steel reinforcement bars. In chloride-contaminated intact concrete the service life as a result of using hot-dip galvanised reinforcement bars is 3-5 times longer compared with ordinary steel reinforcement bars. The conclusion is based on the results received with the critical water-soluble chloride content, 1.0-1.5 wt%CEM, which is substantially higher than the critical water-soluble chloride content, 0.3-0.4 wt%CEM, for ordinary steel reinforcement bars.

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hot-dip galvanised concrete reinforcement, crack width, corrosion mechanisms, service life

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https://urn.fi/URN:ISBN:978-952-248-168-9

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[diss] Insinööritieteiden korkeakoulu / ENG