Concrete Spalling
Concrete Spalling
(OP)
I have an existing concrete beam (interior) that is subject to constant high temperatures (around 142F, 62C). At the interface between the roof deck and the beam, concrete is spalling from the face of the beam. There is no visible stress cracks on the surface of the beam, the beam has not been subject to a fire, yet the spalling does not extend to the reinforcing steel within. The concrete used was normal density concrete, 5000#/si. Concrete cover to the steel was to be 2". The depth of the spalls are less than 2" in many areas, and where they extend deeper into the beam 2-2.5", no rebar has been exposed.
Any ideas as to the cause of the concrete spalling?
Any ideas as to the cause of the concrete spalling?






RE: Concrete Spalling
RE: Concrete Spalling
Can you tap the spalled areas with a hammer? If the area has a hollow sound it's possible that the rebar is corroding, which is a cause for spalling.
Do you have any photos?
RE: Concrete Spalling
What is the average humidity in the area? The warmer air will hold more moisture that could condense on cooler exterior surfaces.
Dick
RE: Concrete Spalling
It is likely that your spalling is caused by differential movement. Freeze thaw isn't at play here and carbonation is a possibility, but the depth of spalling is too deep to be primarily influenced by carbonation.
The 142F is not high enough to create an issue with the concrete and also is not high enough to cause sufficient vapor pressure interstitially in the concrete to cause spalling, unless there is some microcracking that occurred during the curing process.
Look at the face of the spalled pieces. If the face shows that the coarse aggregate is fractured, then it is likely that external shearing forces are at work (as the differential movement previously described). If the face shows that the aggregate did not fracture and that the paste pulled from around it, you could have a placement issue, an initial curing issue, contaminated aggregate, or several other mechanisms.
As bridgebuster suggested, a few photos would help.
RE: Concrete Spalling
RE: Concrete Spalling
RE: Concrete Spalling
Dik
RE: Concrete Spalling
RE: Concrete Spalling
In Picture 8, I see a white streak above the spall; that's a somewhat common occurrence in bridge deck construction - a pattern of white lines perpendicular to the stringer/girders. It generally indicates there was too much water in the mix causing the minerals to leach out. Back to the picture, I don't see any fractured aggregate or paste; for the time being I think it's a placement problem.
RE: Concrete Spalling
Check one of the spalled pieces. You'll probably find that it has little or no coarse aggregate in it. There's a good chance that the initial fracture took place when the beam forms were pulled...it just took a while for it to fall off.
If my observations are correct, it is a placement issue as bridgebuster said.
RE: Concrete Spalling
I will take a closer inspection of the spalled pieces to confirm the aggregate or lack of aggregate within the section.
The first spall occurred about 5 months ago and new areas have been occurring since then. No other changes to the atmosphere within the space have occurred.
RE: Concrete Spalling
This could be related to the original placement as others have said, but it would have taken a force, either internal or external, to cause the spalling. As it doesn't look like corrosion of the steel caused it, then movement at the deck level would seem to me the most likely suspect.
RE: Concrete Spalling
Photo 08 does not look like spalling to me, the exposed aggregate is free of grout and shiny, looks more like a retarder has been applied.
The other photo 10, is more like a typical spalling, some force had to be applied. I think it's something to do with the detailing between the beam and the deck.