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Re: Concrete for offshore structures[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Concrete for offshore structures
- From: Tom.Hunt(--nospam--at)fluor.com
- Date: Mon, 1 Nov 1999 08:47:55 -0800
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
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