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Fwd: Corrosion and durability of reinforced concrete[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: wai(--nospam--at)euken.com
- Subject: Fwd: Corrosion and durability of reinforced concrete
- From: rlewis(--nospam--at)techteam.org (Richard Lewis)
- Date: 06 Aug 1997 13:55:58 GMT
Just this morning I attended a CRSI seminar on corrosion of rebar in concrete. The speaker was Donald Pfeifer of Wiss Janney Elstner -- very knowledgeable. WJE is doing a comprehensive study of rebar corrosion for FHWA, begun in 1993 and slated to conclude in 1998. Since there has been some discussion of this topic here recently, I thought I'd summarize the most interesting points for the benefit of the listserver readers. 1. The rapid chloride permeability test (AASHTO T-277) cannot be used to compare the permeability of normal concrete to fly ash, silica fume or slag cement concrete. The differing chemistry of these pozzolans skews the results and makes them appear less permeable than they are. There are currently quite a few lawsuits making their way through the courts because of unrealisticly low (<1000 coulombs)test values specified for concrete. 2. High strength concrete is in some situations (ie, bridge decks) worse than the old 6 bag / 3000 psi concrete. Why? Because it has quicker strength gain, higher modulus and lower creep, so when restrained (by bridge girders, for example) it cracks, where the old concrete would creep. One possible solution is post tensioning. 3. The more cover the better. Chloride content decreases geometricly with cover. Where there is a crack cover is reduced or eliminated, so it is important to minimize cracking and to repair cracks. A MinnDOT study was cited of some bridge decks that received Iowa low slump concrete overlays where were very effective in retarding chloride penetration. 4. Standard epoxy coating is better than black steel. Of the thousands of epoxy rebar structures built in the past 20 or so years, very very few have had problems. 5. For high value or difficult to repair structures in corrosive environments, stainless steel rebar looks promising. It adds 5 to 10% to the initial cost, but predicted life is 75 to 100 years. In England they have had pretty good success with stainless clad rebar. In Europe stainless mesh is reported now being used in tunnel linings. 6. Epoxy coated rebar should be electrically isolated from black rebar. It is common to see an epoxy coated top mat and a black steel bottom mat in bridge decks, or to have a stay in place galvanized form. If these are electrically connected, a galvanic cell is created. [My understanding on this point is not too clear. Would the galvanized deck cause corrosion of the epoxy rebar, or would it act as a sacrificial anode?] 7. Testing is not complete, but the corrosion inhibitor concrete additives look promising. A "belt and suspenders" approach is recommended -- good cover, corrosion inhibitor, and epoxy rebar, for example. I hope you listreaders find this useful. Additions and corrections are encouraged. -Jay B. --- Internet Message Header Follows --- Received: from server1.seaoc.org (bqe.com [184.108.40.206]) by host1.texramp.net (8.8.5/8.8.5) with SMTP id LAA04951 for <rlewis(--nospam--at)techteam.org>; Wed, 2 Apr 1997 11:23:21 -0600 (CST) Received: from mail3.voicenet.com by server1.seaoc.org (NTList 3.02.10) id za016197; Wed, 2 Apr 1997 09:18:10 -0800 Received: from omni.voicenet.com.voicenet.com (cherryhill155.voicenet.com [220.127.116.11]) by mail3.voicenet.com (8.8.5/8.6.12) with SMTP id MAA15998 for <seaoc(--nospam--at)seaoc.org>; Wed, 2 Apr 1997 12:20:15 -0500 (EST) Message-ID: <33429427.E75(--nospam--at)voicenet.com> Date: Wed, 02 Apr 1997 12:15:19 -0500 From: John Bryan <jaybryan(--nospam--at)voicenet.com> Reply-To: seaoc(--nospam--at)seaoc.org X-Mailer: Mozilla 3.0 (Win95; I) MIME-Version: 1.0 To: seaoc(--nospam--at)seaoc.org Subject: Corrosion and durability of reinforced concrete Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit 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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