Question

How does concrete react to aluminum? Also, why should you not allow the use of aluminum wire for tying rebar?

Answer

Aluminum will react with the alkalis in concrete and produce hydrogen bubbles when curing. This causes the concrete to expand. Some admixtures include aluminum on purpose to produce expansive concrete. Aluminum cast into concrete will corrode. The corrosion will result in expansion and cracking. Over time aluminum tie wires will corrode and can cause enough localized stress to cause spalling immediately over the tie locations.