Concrete Crack Tolerance
Concrete Crack Tolerance
(OP)
I'm looking for a standard for acceptance of concrete structures pertaining to concrete crack widths or severity. For example, a concrete lined channel has developed severe cracks while curing. Is there a typical rule of acceptance?





RE: Concrete Crack Tolerance
I am assuming that the channel is used for storm water run-off, and that it is not reinforced (or very lightly reinforced) and well-sloped. You should try to etablish whether the cracks are all the way through the concrete. If they are, you could end up with some washout below the concrete. Surface cracks are not necessarily an immediate problem, but will probably escalate to full-depth cracks, especially in freezing climates.
One way to test if the cracking is severe enough to warrant repairs is to block the water flow through the channel and fill it with water. The rate that the water escapes or leaks out of the channel should not visible, or more than is judged acceptable. This could be repeated at several intervals to test the entire channel.
Let me know if my assumptions are wrong and if the use is more critical than I have guessed.
RE: Concrete Crack Tolerance
Interior - max. 0.014 inches
Exterior (normal exposure) - max. 0.010 inches
Exterior (aggressive exposure)- max. 0.006 inches
This was put forth by Kesler, et al in a Bulletin from the University of Illinois Engineering Experiment Station in 1965. This is consistent with current ACI guidelines.
Your application would probably fall in the "aggressive" exposure range. I have used this tolerance scale for evaluation of Sewage Treatment plants and other aggressive exposures.
RE: Concrete Crack Tolerance
RE: Concrete Crack Tolerance
Since the cracks were closely spaced, could have been initiated/exacerbated by "plastic" shrinkage, though they are likely following a rebar pattern. Look also for slumping directly over the rebar. This causes a reduced cross section, susceptible to early cracking.
RE: Concrete Crack Tolerance
Your Classification of "Aggressive" Exposure range was not looked at until your comment.
Thanks for the help!
RE: Concrete Crack Tolerance
RE: Concrete Crack Tolerance
RE: Concrete Crack Tolerance
Your crack spacing implies that perhaps the welded wire is "wavy" or sits variable in depth of the cross section.
RE: Concrete Crack Tolerance
I have another question along the same lines.
I am constructing a reinforced concrete box culvert outlet works for a dam. The specs call for control joints with waterstops every 40'. Adjacent pours must wait for a full 7 day cure prior to pouring the next section. The contractor is asking if 5 days is sufficient (to get back on schedule). My question is - How critical is the 7 day curing period for drying shrinkage? Research I have read studied drying shrinkage and plotted from 1 month to 33 months. So how much actual shrinkage occurs in the first few days? The concrete is spec'd at 4,000 psi with .45 w/c and 1" max agg. Type I/II cement with air entrainment. Daytime temperatures will reach up to 110 degrees F. 3 and 4 day compressive strengths of the trial mixture are over 4,000 psi.
RE: Concrete Crack Tolerance
gives the following for tolerable crack widths:
exposure tolerable crack width (inch)
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dry air or protective membrane 0.016
humidity, moist air, soil 0.012
deicing chemicals 0.007
seawater, wetting and drying 0.006
water retaining structures 0.004
RE: Concrete Crack Tolerance