Can aluminum alloy be an alternative to steel for reinforcement in terms of the same forces encountered by reinforced concrete beams? Will it be economical and feasible?

Are there organizations who already practices the use of aluminum alloy reinforcement as a replacement to steel?

  • $\begingroup$ Do you mean using aluminium for rebar in reinforced concrete? $\endgroup$ – Wasabi Nov 24 '16 at 9:47
  • $\begingroup$ As far as I remember from an Aluminum Course during university, there is also a concern in terms of fires. The low melting temperature of Aluminum makes it a bad material for buildings. Also, I remember that the Aluminum Oxide is actually helping to make it more resistant, but there are other implications which I don't remember. $\endgroup$ – Physther Nov 24 '16 at 11:44
  • $\begingroup$ You might like to check out this one: vbn.aau.dk/files/57365894/Construction_in_Aluminium $\endgroup$ – Physther Nov 24 '16 at 14:04
  • $\begingroup$ @Wasabi, Yes, precisely. $\endgroup$ – Trekslofar Nov 24 '16 at 14:09
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    $\begingroup$ A lot of folks are approaching this from the point of view of disadvantages. From another perspective, an important question is "what problem does aluminum solve?" If there isn't a solid, evidence-based answer to that question, then there is no reason to further consider aluminum. $\endgroup$ – wwarriner Nov 24 '16 at 16:28

A very important property of steel used in reinforced concrete is that it has similar coefficient of thermal expansion as concrete:

  • Concrete: $14.5 \cdot 10^{-6} \frac{m}{m\,K}$
  • Steel: $12.0 \cdot 10^{-6} \frac{m}{m\,K}$

Compare this with:

  • Aluminum: $22.2 \cdot 10^{-6} \frac{m}{m\,K}$

So a likely result of putting aluminum inside a concrete beam would be the concrete cracking when the aluminum expands more in the summer.

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    $\begingroup$ This seems like one of the likely reasons. Paul's comment about the low melting point also seems relevant. My thought was also fatigue. No matter how you load aluminum it will eventually weaken under cyclic loading. I'm not sure how cyclic you consider building loading, but it's probably a concern since you can exactly go in and replace all the stressed rebar. $\endgroup$ – JMac Nov 24 '16 at 12:28
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    $\begingroup$ Another disadvantage (though not necessarily a deal-breaker such as the issues already raised) is that aluminium's elastic modulus is almost a third of structural steel's (~69 GPa vs ~200 GPa). This means that the concrete would need to crack three times as much in order to generate the same tensile stress in the rebar. $\endgroup$ – Wasabi Nov 24 '16 at 14:38

In short: you can't use aluminium to reinforce concrete. You shouldn't even embed uncoated aluminium in concrete.

Quoting Corrosion of Non Ferrous Metals in Contact with Concrete, "Aluminium suffers attack when embedded in concrete". Corrosion of aluminium embedded in concrete causes total destruction of aluminium bars, therefore it's dangerous and inadvisable to use aluminium as rebar.

I don't have the reference at hand (I think it was in this book) but I remember having read about some accident caused by use of aluminium as rebar during a shortage of steel caused by some strikes in the USA. Aluminium bars examined after accident had completely disintegrated leaving just some white powder.

Update: I got the book again. My memory stated above is inexact, although the conclusion doesn't change. The book is Feld, Jacob. "Lessons from Failures of Concrete Structures". American Concrete Institute. Detroit 1964.

According to it, during the steel strike in 1959 several buildings in New York substituted aluminium conduit for the conventional steel item. It resulted in distress with cracking ceilings along the conduits due to aluminium conduits expansively disintegrating into white powder.

As you can see, the reference was about aluminium conduits instead of aluminium rebar. However, aluminium rebar in concrete would result in the same effects: disintegrating bars, therefore losing all strength and breaking concrete due to expansion.

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  • $\begingroup$ Aluminium is highly corroded by sodium hydroxide and Hydrochloric acid.Other bases and acids would maybe have a similar effect.The reaction is exothermic with generation of lot of heat.(goes up till 90degree celcius I think).If bases or acids from everyday use should trickle in to aluminium reinforced concrete mayhem would occur. $\endgroup$ – Chappy May 12 '17 at 3:42
  • $\begingroup$ Maybe this was the reason for the disintegration of aluminium that you mentioned. $\endgroup$ – Chappy May 12 '17 at 3:43
  • $\begingroup$ Also hydrogen gas which is highly combustile gets released in these reactions. $\endgroup$ – Chappy May 12 '17 at 3:46

Al is more expensive than regular steel per unit strength. Plus, the reason steel is used in direct contact with concrete is the coincidence of the thermal expansion rate of the two materials at typical temperatures. IOW, Aluminum would crack concrete when it expands if the Al were inside the concrete. However, if you allow for movement between the two materials, say, design the structure so one can slide over the other, in certain applications, yes, Al can be used. For example, you might use an Al roof on a concrete-walled structure.

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  • $\begingroup$ Its not a coincidence, it was engineered. $\endgroup$ – joojaa Jun 10 '17 at 23:09

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