Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Concrete for offshore structures

[Subject Prev][Subject Next][Thread Prev][Thread Next]

Mr. Mufti,

Since your structure will be exposed to seawater you need to be concerned about
sulfates and chlorides.  High concentrations of sulfates will attack the cement
matrix and high concentrations of chlorides will accelerate the corrosion of the
rebar.  Typical seawater will have approximately 2000 ppm sulfate and 20,000 ppm
chloride.  This will vary from the Pacific to the Atlantic AND is significantly
higher in the Arabian Gulf.  I suggest you get a chemical analysis of the water
at your site.

Type II and V cements are for moderate and severe sulfate concentration.  Per
ACI 318, Table 4.3.1, 2000 ppm would be considered "severe" requiring Type V
cement.  However, this will not help any for your corrosion potential from the
chlorides.  For this you would typically call for extra concrete cover (say 3
inch for all rebar), water/cementitious ratio less than or equal to 0.40 and
probably a mineral additive such as fly ash, blast slag, or silica fume.  Note
that per PCA studies on sulfate resistant concrete, if you have a w/c ratio of
0.40 and a mineral additive the cement type will have little effect on sulfate
resistance.  Cement type is only beneficial when the w/c is around 0.45 to 0.55.
You may as well use Type I cement and spec the additional durability
requirements.

Thomas Hunt, S.E.
Fluor Daniel





"M. A. Mufti" <mam(--nospam--at)cyber.net.pk> on 10/29/99 10:29:09 PM

Please respond to seaint(--nospam--at)seaint.org

To:   seaint(--nospam--at)seaint.org
cc:    (bcc: Tom Hunt/AV/FD/FluorCorp)

Subject:  Concrete for offshore structures



What kind of cement is reecommended for use in offshore structures,
Ordinary
Portland Cement or Sulphate-resisting cement?
Also, for land-based structures adjacent to sea, substructure as well as
superstructure?
M. A. Mufti