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Concrete crack control

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ACI committee 350 report titled "Environmental Engineering Concrete
Structures"  for water retaining structures has recommendations.  A chart
from this report is included in the 1992 edition of  CRSI Manual.  I
frequently less a less conservative guideline that was published in the
October 1984 edition of Concrete International for structures that do not
retain water.  I don't remember who authored that article.  It recommended
the following ratios of steel area to concrete area based on various joint
spacings:
	.0018	20 ft
	.0027	30 ft
	.0033	40 ft
	.0037	50 ft
	.0040	60 ft
For a wall where appearance is very important, as in your case, I would
recommend following the ACI 350 recommendations as a minimum.  That would
require a ratio of .0022 for 20 ft, .0033 for 30 ft and .0042 for 40 feet.

Roger Davis
SDS Architects, Inc.



Jeff Smith" <smthengr(--nospam--at)sirius.com
Can anyone suggest a good reference for concrete crack control in exposed
concrete walls. Are there any rules of thumb for crack control as a function
of strength, w/c ratio, type of aggregate, type of forms, spacing and size
of control joints, etc.
We just finished a 20 foot section of 11' tall, 10" wall, double curtain
reinf,  that will not be exposed, but was used as a mock up for a future
pour.
We had a .43 w/c ratio, 3/4 aggregate, 5500 psi mix with poly fibers, using
mahogany forms on one side and ac ply on the backfill side. The finish looks
like it was steel troweled, glassy smooth. However, there are two 8' long
vertical hairline cracks that occur between snap ties about 4-6' apart. The
crack does not extend to the back side of the wall.
The 4.1 Point Richmond quake was a few days after the pour, I can't believe
that was what caused it. We already completed an orthogonal wall that was
about 40' long that was board formed, no control joints, using pea gravel
that has no cracks in it. 17 day compression test was 4300 psi.
Thanks,

Jeff Smith