Why do highway builders allow rebar to rust before pouring ...
May 28, 2016· Corrosion of the rebar will only resume if the concrete cracks over time and oxygen and moisture once again can get to the rebar. It is important this does not occur once the concrete is in place because iron oxide ( Corrosion product ) occupies a larger volume than iron, it is less dense than iron; so will crack the concrete as it forms.