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Monitoring of Reinforcement Corrosion in Field Exposed Concrete Blocks
Abstract
Three concrete blocks instrumented with rebars, anode ladders and other sensors have been produced and exposed to sea water in Fehmam Belt field exposure site in Roedbyhavn in Denmark. The corrosion activity on the anode ladders is continuously monitored by measurements of half-cell potentials and linear polarisation resistance. The design of the instrumented concrete blocks is presented together with the first results after 2 years marine exposure. Corrosion initiation on anodes with small concrete cover has been identified from the electrochemical measurements and verified by visual inspection. Chloride profiles have been measured for three different binders.
Supplementary resource (1)
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A Danish Expert Center for infrastructure constructions was established in 2010 setting a platform for cooperation between the Danish Technological Institute and the Technical University of Denmark for the study of durability of reinforced concrete in aggressive environments. The cooperation runs over a three year period, with primary focus on the degradation processes in concrete resulting from exposure to chlorides, either from marine or de-icing salts environments. The ambition is to continue the cooperation based on funding from EU´s 7th and 8th framework programme. The paper outlines the approach adopted in the Expert Center and the activities initiated, providing background motivation and some ideas for overcoming different unresolved issues. However, results so far, mainly concerning the effect on durability of selected critical structure details, such as vibration, joints and concrete spacers, are presented. Self-Compacting Concrete has been studied against conventional slump concrete with respect to critical structure details and found to show similar performance on all studied subjects, within practically applicable ranges of water dosage (± 5 l/m3).
Uncracked reinforced concrete slabs were field exposed mounted on a floating pontoon and partly submerged for 5 years at the Swedish west coast. The total chloride ingress was analysed at various exposure times at 3 elevations representing a submerged, a splash, and an atmospheric exposure zone. The concrete mixtures varied in w/c ratio, type of cement, and amount and type of pozzolan used in the binder. The data is unique as it represents recurrently measured total chloride penetration profiles at various exposure ages, providing a foundation for the prediction of chloride ingress in concrete in a given environment. The results after 5 years of exposure confirmed the expected inverse relationship between water-to-binder ratio and chloride ingress. The use of 5–10% silica fume in the binder had a very positive effect on reducing the chloride ingress, but little or no benefit at all was found for concrete with fly ash in the binder as compared to the use of 5% silica fume. The chloride penetration rate as expressed by a calculated effective chloride diffusivity has a tendency to decrease over time. High- performance concrete with w/c ≤ 0.4 and a minimum of 5% silica fume added as a well dispersed slurry exhibited an effective chloride diffusivity in the range of 1 × 10−13 to 5 × 10−13 m2/s after 5 years exposure in the splash zone.
Recurrent studies of chloride ingress in uncracked marine concrete at various exposure times and-elevations Aalborg Portlands' durability project – 25 years judgement
- P Sandberg
- D H Bager
[1]
SANDBERG, P., Recurrent studies of chloride ingress in uncracked marine concrete at
various exposure times and-elevations, Div. of Building Materials LTH, Lund University,
Report TVBM-3080, 1998, 48 pages. ISSN: 0348-7911
[2]
BAGER, D.H., " Aalborg Portlands' durability project – 25 years judgement ". Proc. of
Nordic Miniseminar on Nordic Exposure Sites-input to revision of EN 206-1. Hirtshals,
November 12-14, 2008, pp. 119-135. NCR workshop-proceeding No. 8.
ISBN 978-82-8208-013-2
Salt- og temperaturforhold i de indre danske farvande (Salt and temperature conditions in the inner Danish waters)
- I Andersen
Andersen, I., Salt-og temperaturforhold i de indre danske farvande (Salt and temperature
conditions in the inner Danish waters). Danish Meteorological Institute, Copenhagen,
Technical Report No. 94-4, 1994.
Aalborg Portlands’ durability project - 25 years judgement
- D H Bager
BAGER, D.H., "Aalborg Portlands' durability project -25 years judgement". Proc. of
Nordic Miniseminar on Nordic Exposure Sites -input to revision of EN 206-1. Hirtshals,
November 12-14, 2008, pp. 119-135. NCR workshop-proceeding No. 8.
ISBN 978-82-8208-013-2