Challenges in predicting service-life of concrete structures exposed to chlorides

Title: Challenges in predicting service-life of concrete structures exposed to chlorides
Author(s): R.D. Hooton
Paper category : conference
Book title: 2nd International Symposium on Service Life Design for Infrastructures
Editor(s): K. van Breugel, Guang Ye, Yong Yuan
Print-ISBN: 978-2-35158-096-7
e-ISBN: 978-2-35158-097-4
Publisher: RILEM Publications SARL
Publication year: 2010
Pages: 3 - 16
Total Pages: 14
Nb references: 33
Language: English

Abstract: Several service life models exist for prediction of time-to-corrosion of concrete structures exposed to chlorides. Some are more sophisticated than others in terms of addressing the various chloride transport mechanisms, while others assume transport by diffusion alone.

As well, the input variables have uncertainty associated with them such as boundary conditions, cover depths, diffusion coefficients, time-dependent changes, and rates of build up of chlorides at the surface.

But there is disagreement, for example, on how to measure time-dependent changes in diffusion properties, on how long it continues, as well as to what properties influence the time dependent values. As well, imperfect curing can result in depth-dependent effects on diffusion properties. How experimental data is obtained as well as how models handle these properties has a dramatic impact on predicted service lives.

In addition, construction detailing, defects and construction practices can have a significant influence on actual penetration rates, but are rarely quantified or modeled. Very few models deal with the influence of cracks or the fact that concrete in the cover zone will almost certainly have a higher diffusion coefficient than the bulk concrete as the result of imperfect curing or compaction. While many models can account for variability in input properties, they will never be able to account for extremes in construction defects. Therefore, to ensure the reliability of service life predictions and to attain a concrete structure that achieves its predicted potential, designers and contractors need to work together to ensure proper detailing, minimize defects, and adopt adequate, yet achievable, curing procedures. As well, concrete structures are often exposed to other destructive elements in addition to chlorides (eg frost, ASR) and this adds another level of complexity.
This contribution will discuss some of these issues as well as the need to use performance based specifications together with predictive models.

Online publication: 2011-04-20
Publication type : full_text
Public price (Euros): 0.00

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