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[SEAOC] Re:Concrete cracks

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>What I would like to know is, are ANY cracks in concrete serious? 

(A)
If a crack is serious or not is depending on
  The "amount" cracks (length, width, depth and how often they appeare)
  The type/direction of cracks
  The enviroment (Cl-, CO2 ...)

(B)
The making of a crack is (simply said) either
  Shrinkage (it's natural for conrcete to loss volume in the hardening prosess)
  External forces or damages

If you have a few vertical shrinkage-cracks in a basement wall (vertical and
long cracks) - it would not affect the structure's capasity. If the crack
goes all it to the rebars, and the envirolent is aggressve (like salt, Cl-)
then the crack could leed aggressives to the rebar and then you got a
corrosion problem.

You can not say if one type crack is harmless and one other is not. Some
types of cracks (like "crushing"-cracks due to overload) are more "risky"
tahn others (shrinkage craks)  - but the whole situation (See A above)
determines if this is a harmess crack or not.

The ONE thing one must have in mind is:
  If the structure has rebars and is exposed to aggressives (CO2, Cl- ...)
you must seal off the crack to redusxe the risk of aggressives attacking the
rebar.
(This would normally apply to all outdoor structures in a cold/temperate
climate.)

PS! If the structure is exposed to frost and water, then cracks could reduse
the freeze/taw resistance.

Oyvind Saeter - oes
____________________________________________________________________________

Mr. Øyvind Sæter    (Alternative: OEyvind Saeter)
M. Sc. in Civil Engineering - Structural Analysis and Concrete Technology.

Email: oysater(--nospam--at)sn.no | oes(--nospam--at)pvv.ntnu.no | oes(--nospam--at)pvv.unit.no
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