What is the long term effect of organic materials in concrete?

[Stephen Tashiro]

What is the long term effect of organic materials like pine needles, leaf fragments, hair, etc that are trapped inside hardened concrete? Do they decay and make the concrete weaker? Or is any weakening due to the fact that these are weak in the first place, so the passage of time doesn't make much difference?

People make lightweight "hypertufa" objects out of concrete mixed with peat moss. I supposed peat moss is already decayed to large extent.

[Jim Rimmer]

I'm not a concrete expert but I would guess that eventually the material would decay and leave a void (just like dirt clods that wash out). Depending on the amount of materila, it may or may not weaken the concrete. s to the peat moss, I have no idea.

[Mel Fulks]

Probably much like the Romans of Pompia in AD 79, gone but making a permanent impression.

[Jim Koepke]

This could be looked at as a sequence of logic.

If they made concrete stronger, long reach but here for the logic, then it would be in structural concrete.

Same if they had no effect on concrete.

So we can guess these do not "improve" the structural qualities of concrete. Builders are always looking for materials to add to concrete to lower costs.

Artist mixing peat moss with concrete is mostly to lower the weight of the objects they are making.

My guess is the passage of time will not make a difference unless a crack in the concrete is helped by the foreign object in the concrete.

jtk

[Myk Rian]

I have a theory that Jimmy Hoffa is part of a bridge abutment on the Chrysler Freeway in Detroit. (They were pouring it the night he disappeared. Really)
I also expect that abutment to collapse at any time, due to the huge void his body left in it.

[Larry Frank]

I would assume that the organic material would decay and leave a void. Depending where the concrete is would make a big difference. If you are up north, the void could hold moisture or water and when it freezes would cause a crack.

[Dave Ray]

Steve are you worried about hiding a body? Nah, I just watch to mant cop shows on TV.

[Stephen Tashiro]

Steve are you worried about hiding a body?

No. I'm not worried about that "bricks without straw" thing either.

[Curt Fuller]

Stephen, here in Utah we go to great lengths to keep any organic material out of the concrete. The company I work for has several gravel pits. One is clean enough that the material is just crushed and screened for the proper gradation. The others wash the fine silt out of the sand. But that said, most of our concrete that is to be placed outdoors is air entrained, which is done by chemicals that are basically like detergent and form microscopic bubbles in the concrete. 6% plus or minus 1% is the standard target for air, so basically 6% of the concrete is air. If concrete is placed at low slump (drier) and not vibrated it also gets entrapped air. That's the little bubble like marks you see on the surfaces that were against the form and in extreme cases the honeycomb you see where the rocks are exposed. All those things would have the same general effect as having sticks, leaves, mud or whatever other organic material was in the concrete.