- Q.All of the foundation specs
we build on require rebar to be free of rust and mill
scale. For years this hasn’t been an issue,
until recently when a project manager called us on it.
All we can think to do is wire brush the entire lot of
rebar. Is this really necessary?
responds: Fortunately, there are a couple of
standards you can cite in your defense. The ASTM
standard for deformed steel reinforcement (A706)
and the Concrete Reinforcement Steel Institute
(CRSI) Manual of Standard Practice both
give the same recommendation: Reinforcing bar with
rust, mill scale, or a combination of both is
satisfactory, provided the minimum dimensions,
weight, and height of the deformations (the formed
protrusions on the bar) of a hand-wire-brushed test
sample are not less than the values specified in
the standard. In other words, if the rust or mill
scale is light, it will not affect the bond to the
concrete. In fact, studies have shown that mill
scale and light rust enhance the bond between
concrete and steel.
Tim Fisher is the field engineering editor
for Aberdeen’s Concrete Construction