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RE: Concrete Cracks.

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Since you asked...

ACI 224 (Control of Cracking) used to list 'tolerable' crack widths for
well-designed R/C structures, depending on the exposure condition. For
interior (dry) exposures, a width of 0.016" (0.41 mm) was given. This
correlates reasonably well with the EC3, which limits interior cracks to 0.3
mm. You can arrive at the same number by working backwards with the (now
defunct) Z factor of 175 in ACI 318 for min. flexural reinforcement (see
318-95 10.6.4).  ACI 318-99 has dispensed with the Gergely-Lutz equation and
Z factors. Interestingly, in the commentary, you now find the following
statements: "The role of cracks in the corrosion of reinforcement is
controversial. Research shows that corrosion is not clearly correlated with
surface crack widths in the range normally found with reinforcement stresses
at service load levels. For this reason, the former distinction between
interior and exterior exposure has been eliminated." and "The new provisions
for spacing are intended to control surface cracks to a width that is
generally acceptable in practice but may vary widely in a given structure."

Regards,  John


-----Original Message-----
From: npitera(--nospam--at)mmm.com [mailto:npitera(--nospam--at)mmm.com]
Sent: Friday, December 15, 2000 09:11 AM
To: seaint(--nospam--at)seaint.org
Subject: Concrete Cracks.




In concrete, there are cracks, and then there are CRACKS. For beam shear
cracks,
at what width limit does one consider the crack to be "hairline",0.
003",0.005"
0.007"?

Any comments are great appreciated.

Regards,

Nick.