Wall Reinforcement shadow lines

[ahunt]

Good Morning,
I have an odd question. We have a job that includes a wall with 2" of over on the outer most rebars. After form striping, you can see shadow lines of the resteel in the walls. Anyone else run into this?

I have a couple ideas, but they seem far fetched.

A.

 

[PMR06]

I saw this same thing on an elevated slab we did. The contractor said the rebar was hot when the concrete was poured, and the concrete around the bars dried and shrunk faster than the surrounding slab. It was over 100 degrees the day of the pour, and I imagine the bars baking in direct sun were even hotter. With a wall though, I would think the forms would keep things cool, and this hypothesis may not apply.

It could also be from form oil that was sprayed after the wall bars were placed, in which case the bars blocked the spray from the panels.

 

[jike]

This is sometimes called "ghosting". Wetting the surface will generally make it more noticeable.

 

[blake989]

typical on the back side of heavily reinforced tilt up walls, I was told it is an accumulation of fine aggregates on the underside of the steel when poured. CIP wall, maybe a little less cover than spec'd.

 

[hokie66]

I am inclined to think PMR06's suggestion about the form oil may be the answer, especially if the pattern you are seeing is both horizontal and vertical bars. Would indicate that they forgot to oil the forms before placing the reinforcing mat. Contractor should be able to tell you or find a worker who remembers.

If there was cracking along the horizontal bars, that would be poor consolidation and/or plastic settlement cracking.