Curing concrete in "carbonated water"

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b)A Reinforced concrete (RC) sea wall has been in operation for 45 years and shows Visible signs of brown staining and spalling of the surface concrete around the Bottom two thirds of the height on the seaward side and similar damage on the Top section exposed on the roadside as indicated in Fig. Q1 c) below:

Fig. Q1 c) RC Sea wall

  1. Comment on the level of exposure and describe the Most likely cause of the damage.

    Answer 1 b) i):

    The level of exposure in a coastal Environment can be severe and problems can arise due to a number of factors:

  • Erosion of the concrete surface due to wave action And abrasion due to sand being picked up and impacted against the sea wall.

  • Ingress of sea water under pressure with tidal Movement and wave action (hydrostatic and hydrodynamic).

  • The sea water contains salt which can penetrate the Surface cover of the concrete reinforcement leading to chloride attack.

  • Chloride attack lowers the pH reducing the level of Alkalinity.

  • This de-passivates the steel and compromises the Stable oxide layer which normally prevents pitting corrosion.

  • Water ingress and potential for freeze-thaw cycling Where water freezes and expands setting up tensile stress near the surface of The concrete cover.

  • Chloride attack due to salt water is the most Probable cause of the corrosion staining and spalling on the seaward side.

  • Additional sources of CL- ions from the Use of de-icing salts in the winter on the roadside.

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