Keywords: concrete, durability, corrosion, chlorides, moisture, diffusivity, damage.

Chloride induced corrosion is one of the most cited cause of durability loss and strength degradation of reinforced concrete structures under service conditions [1,2,3,4,5,6,7]. In accordance with a conceptual steel corrosion sequence model advocated by Tuutti [6], the durability capacity of the concrete structure is significantly limited to the corrosion initiation time of the steel reinforcement in concrete. For the chloride exposures, it follows therefore that the forecast of the service life loss problem is closely related to ascertaining the corrosion initiation time that is very much dependent on the diffusivity property of the concrete.

The characteristic behaviour of the chloride diffusivity has been investigated across a number of studies that more often lack cohesive coverage with regard to the coupling effects relevant to the chloride transport problem. More specifically, the coupled rather than disparate roles of concrete quality based influence factors, including the mechanism of water migration in concrete, under field service conditions are often ignored for formulation and implementation difficulty reasons. This paper is therefore concerned with implementation of a requisite methodology to predict the service life in terms of time from initiation of chloride-induced corrosion in concrete under service conditions.

A major feature of this study is consideration of the non-linear effect that moisture interaction exerts over the combined diffusivity influence functions ascribed to some concrete quality factors elected for analysis. A framework of finite element based computer software ConTra2D has been developed so as to allow for the direct exploration of the problem to be drawn from a phenomenological database of diffusivity functions [7]. Results of the analysis show that confluence of the material quality based influence functions, including water-cement ratio, cement or binder content, and equivalent maturity or curing time besides the coupling effect of moisture, is significant to proper understanding of the durability performance of concrete structures against chloride ingress and hence associated initiation time of corrosion problems in the field.

1

C.L. Page, K.W.J. Treadaway, "Aspects of Electrochemistry of Steel in Concrete", Nature, 297, 109-115, 1982. doi:10.1038/297109a0

2

H.E. Townsend, H.J. Cleary, L. Allegra, "Breakdown of Oxide Films in Steel Exposure to Chloride Solutions", Corrosion - NACE, 37, 384-391, 1981.

3

G.J. Verbeck, "Mechanism of Corrosion in Concrete", Corrosion of Metals in Concrete, ACI SP-49, 1975.

4

P.K. Mehta, "Concrete Structure, Properties and Materials", Prentice-Hall, Inc., 1993.

5

E.J. Fasullo, "Infrastructure: The Battlefield of Corrosion", Corrosion Forms and Control for Infrastructures, ASTM STP 1137, 1-16, 1992. doi:10.1520/STP19751S

6

K. Tuutti, "Corrosion of Steel in Concrete", Swedish Cement and Concrete Research Institute, Stochkolm, 1982.

7

M.A. Shazali, "Computational Chemodamage Transport Modeling of Durability Synergies in Concrete", Ph.D. Dissertation, Civil Engineering Dept., King Fahd Univ. of Petroleum & Minerals (KFUPM), Saudi Arabia, 2004.

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