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     All of the previous advise on your seawater structures has been sound. 
     I would emphasize that most time to corrosion studies indicate that 
     the concrete cover has the most significant influence.  It is not 
     uncommon for marine structures in the Arabian Gulf to have 4 inch 
     cover.  I would certainly push for a minimum of 3 inches to all rebar.
     
     Silica fume produces significantly improved durability, which I would 
     recommend, but note that it causes a reduction in bleed water so you 
     need to be very careful during curing.  Wet curing is almost a must to 
     prevent surface drying cracks.  Fly ash is not bad, does not effect 
     the curing much, but is not nearly as good as silica fume.
     
     As far as corrosion inhibiting admixtures go there are two main 
     players with two very different products.
     
     W.R. Grace has an inorganic product consisting of calcium nitrite 
     called DCI. DCI has been around for nearly 15 years and has been 
     through a lot of testing both in the lab and in the field (just ask 
     them!?!).  One of its advantages is that it raises the corrosion 
     potential of the rebar even if there are "mixed in" chlorides.  That 
     is, even if your water or aggregate are chloride contaminated it is 
     still effective.  One of the disadvantages is that it is a significant 
     accelerator.  In fact, W.R. Grace's accelerating admixture is the same 
     identical product with different labeling.  Grace does make DCI with 
     an added retarder that they claim has a neutral set.  This is like 
     having your foot on the brake and the accelerator at the same time.  
     It is only neutral at 70 degrees in someone's lab back East.  For the 
     past ten years or so Grace has recommended their product at 4 to 6 
     gallons per yard.  To be competitive with Master Builders new product 
     they now recommend their product at 2 to 3 gallons per yard and 
     justify it with a lot of smoke and mirrors using Fick's Second Law of 
     Diffusion.  Studies in Japan indicate that calcium nitrite at low 
     dosages can be dangerous.  If the chloride concentration is high 
     enough to overwhelm the calcium nitrite then corrosion can accelerate 
     at a rate faster than if there were no calcium nitrite in the first 
     place.
     
     Master Builders has an organic admixture called Rheocrete 222+ that is 
     added at only 1 gallon per yard.  It is a combination of Amines and 
     Fatty Acids.  It is duel acting in that the amines have an ionic 
     attraction to the steel raising its corrosion potential and the fatty 
     acids act as a hydrophobic pore blocker (like adding Thompson's Water 
     Seal).  Rheocrete 222+ is not effective against "mixed in" chlorides 
     but has the advantage that it has a neutral effect on setting and 
     curing.  Master Builders also uses Fick's Second Law of Diffusion to 
     determine time to corrosion but I think their approach is more 
     theoretically correct.  Rheocrete 222+ is only about 7 years old so 
     there are no long term studies.  It was used recently in the new 
     Denver Airport.
     
     Both of these products have been tested by numerous agencies and labs 
     and most conclude they do what they claim at the right dosages.  The 
     long term cost benefit is a tough decision.  These products are not 
     cheap.  We recommended Rheocrete 222+ on a recent Arabian Gulf Project 
     but then the Gulf is about twice as saline and a lot hotter than the 
     Pacific Ocean.
     
     Good Luck,
     
     Thomas Hunt



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Subject: Corrosion Inhibitors
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