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- To: wai(--nospam--at)euken.com
- Subject: Fwd: Corrosion Inhibitors
- From: rlewis(--nospam--at)techteam.org (Richard Lewis)
- Date: 05 Aug 1997 15:33:11 GMT
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 --- Internet Message Header Follows --- Received: from server1.seaoc.org (bqe.com [18.104.22.168]) by host1.texramp.net (8.8.5/8.8.5) with SMTP id TAA22608 for <rlewis(--nospam--at)techteam.org>; Tue, 25 Mar 1997 19:40:23 -0600 (CST) Received: from juliette.fabrik.com by server1.seaoc.org (NTList 3.02.10) id za010893; Tue, 25 Mar 1997 16:34:21 -0800 Received: from primus.fabrik.com ([22.214.171.124]) by juliette.fabrik.com (post.office MTA v2.0 0813 ID# 0-0U10) with ESMTP id AAT115 for <SEAOC(--nospam--at)seaoc.org>; Tue, 25 Mar 1997 16:05:24 -0800 Received: by primus.fabrik.com (Fabrik F07.0-000) id Megw.1039622 ; Tue, 25 Mar 1997 15:52:19 -0800 Date: Tue, 25 Mar 1997 15:12:00 -0800 From: "Hunt, Tom" <tom.hunt(--nospam--at)fluordaniel.com> Subject: Corrosion Inhibitors To: SEAOC(--nospam--at)seaoc.org Message-ID: <Megw.1039622(--nospam--at)primus.fabrik.com> Reply-To: seaoc(--nospam--at)seaoc.org Error-To: seaoc-ad(--nospam--at)seaoc.org X-Loop: seaoc(--nospam--at)seaoc.org X-Info: [SEAOC] Owner: seaoc-ad(--nospam--at)seaoc.org X-POP3-Rcpt: seaoc-ad(--nospam--at)seaoc.org X-Sender: seaoc-ad(--nospam--at)seaoc.org Precedence: list X-ListMember: rlewis(--nospam--at)techteam.org [SEAOC(--nospam--at)seaoc.org] __________________________________________________ Richard Lewis, P.E. Missionary TECH Team rlewis(--nospam--at)techteam.org The service mission like-minded Christian organizations may turn to for technical assistance and know-how.
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