How do metals react with concrete?

Fleur(z5)August 24, 2005

I'm making lots of leaves to donate to an organization for a fundraiser. Someone suggested putting a stake on the back side so the leaves will stand up. I'm rejecting that idea on the basis of too much pressure put on the leaf and possibly breaking it.

My idea is to use two links of sturdy chain. Most of one link would be embedded and the other one would be left loose so it could be put over, perhaps a piece of rebar bent so that the tip would point up, then a right angle for an inch or two, then another right angle going down (into the ground). I suppose the loose link could also be considered to be a hanger of sorts. Depending on the length of the rebar, the leaf could float above plants in the garden or sit on the ground.

So my question is, would the chain react badly with the concrete?

Hope I didn't confuse too many people with my description.

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Belgianpup(Wa/Zone 7b)

Lynn Olson, longtime concrete artist, says in his book, Sculpting with Cement, that steel (esp galvanized) is extremely stable in concrete as long as it is in complete contact with it, but steel that is coated with another metal can corrode. Copper, bronze & brass may retard setting where they contact the concrete, but they are stable in it. Nickel, chromium, silver & tin resist corrosion. But aluminum corrodes in cement, and it stretches 3 times as much as steel under the same stresses.

Sue

    Bookmark   August 25, 2005 at 12:18AM
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Fleur(z5)

Belgianpup -- Does he have any suggestions for embedding a hook or loop in the back of a leaf for hanging on a wall or shepard's hook?

    Bookmark   August 25, 2005 at 6:34AM
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tango88(z8TX)

The following is the text from an uncopyrighted online document titled "Corrosian of Non-Ferrous Metals in Contact With Concrete or Mortar". Very good data that should help answer many of your questions:

Aluminum (Al)

Embedded aluminum roof flashing, aluminum water stops, aluminum electrical conduit, introduced aluminum powder (sometimes used to foam concrete), or embedded structural aluminum shapes may all corrode in concrete or mortar. In all cases, a reaction that forms aluminum hydroxide and hydrogen gas occurs, and may cause expansion and cracking of the concrete or mortar. The common use of calcium chloride (or other alkali compounds), and dampness of the concrete increases the reaction rate. Usually, coating the aluminum with bituminous paint, impregnated paper or felt, plastic, or an alkali-resistant coating will prevent or sharply reduce the corrosion.
Copper (Cu)
Copper embedded in concrete and/or mortar is usually roof flashing. Embedded copper is practically immune to reaction with corrosive alkalis, even if exposed to constant moisture. Copper will not react with dry, hardened concrete and/or mortar. Rainwater leaching, however, may bring chlorides in contact with the metal. Corrosion may occur and result in a green discoloration or runoff. Consequently, chloride admixtures should not be used in concrete if contact with copper is expected.
Lead (Pb)
Lead will always corrode when in contact with fresh concrete and/or mortar. The high pH from calcium hydroxide is the cause of the corrosion. Cured, seasoned concrete or mortar will not react with lead. Corrosion of embedded lead flashing in mortar joints will usually result in the production of a lead oxide, a white discoloration. A special case of lead corrosion, called differential aeration, occurs when a lead strip is partially embedded in concrete so that part of the strip is exposed to air. The embedded section has a different electrical potential than the section exposed to air. The result is that the strip will become polar in the presence of moisture. Gradual corrosion and disintegration of the embedded lead will then follow. In such a case, and in all other cases, the embedded portion should be coated with epoxy, varnish, asphalt, or pitch.
Zinc (Zn)
Zinc is highly reactive with alkalies and will deteriorate to some degree upon contact with fresh concrete and/or mortar. The reaction is limited due to a corrosive film that forms on the outer layer of the zinc. It protects the underlying metal from further reaction. Zinc will not react with dry, seasoned concrete and/or mortar. Embedded zinc will react with moisture and calcium hydroxide to produce calcium zincate. Zinc corrosion may also occur when galvanized iron, in the form of flat or corrugated sheets and rebar, comes in contact with fresh concrete and/or mortar. Galvanized iron is coated with zinc, and will react with moisture and chlorides in the concrete and/or mortar to produce zinc chloride. The result is expansion and cracking of the concrete and/or mortar. The metal should be protected with epoxy, varnish, asphalt, or pitch.

    Bookmark   August 25, 2005 at 9:47AM
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billie_ann(6b PA)

Think it's Marly that embeds a plastic straw in the back then threads her wires through the plastic straw. You can use plastic tubing too. Billie

    Bookmark   August 25, 2005 at 10:10AM
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Belgianpup(Wa/Zone 7b)

Fleur, I don't remember that he embeds metal into the surface, although he does add it for surface treatment/decoration. Mainly, he uses it for armature.

I like Marly's experiments with tubing. Even if the tubing broke down, you could still run wire through the opening. I am going to try that multistrand steel aircraft cable that comes embedded in clear vinyl and see what happens. You can often find it on reels (by the foot) at hardware stores. It's very strong.

Sue

    Bookmark   August 25, 2005 at 10:19PM
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Fleur(z5)

I think I'll go the plastic straw or tubing route. I was just looking for a quick fix with the chain links. I've recycled some old, covered copper wire in a few leaves and it seems strong and sturdy but is sort of a pain to twist and embed.

    Bookmark   August 26, 2005 at 3:02AM
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