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RE: Water Retaining Concrete

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First, you should be using 0.25% of the gross wall area to determine your
shrinkage steel.  This would indicate that you are a little light in your
horizontal rebar.

It would be interesting to see what your control joints look like.
Generally, I like to form a joint with a formed V joint on each side of the
wall and cut every other or each horizontal rebar that would otherwise run
through the joint to insure that the crack will occur in the control joint.
Place a water stop in the joint.  It is important to form a weakened
vertical plane.

Now for the bad news.  Your concrete will continue to shrink for about 5
years.  At 28 days only about 40% of the shrinkage has occurred.  At 1 year
80% of the shrinkage has occurred.  If you seal the cracks with an epoxy,
the wall will probably crack somewhere else.  You might want to consider a
material like Sika Fix which seals the crack with a material that reacts
with water, foams up, and remains flexible.

Harold Sprague
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Chance, Acie P. [mailto:acie_chance(--nospam--at)wdi.disney.com]
Sent: Wednesday, September 30, 1998 2:46 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: Water Retaining Concrete


I am designing retaining walls which will form the edges of a lagoon. The
first two walls we poured have cracks which go completely through the wall.
The cracks appear to be shrinkage cracks. The mix design uses 4000 psi
concrete with flyash, super P and well graded aggregate. The walls are
between 10 and 20 ft. high and 2 ft. thick. Vertical steel is # 7 @ 12 back
side and  #5 at 12 water side. Horz. steel is # 5 @ 12 both faces. Crack
control joints are located at 25 ft. O/C. This follows ACI 350
recommendations. I am worried about the damage to the rebar from the
chlorinated water moving through the cracks. We do not intend to waterproof
the lagoon but we do need to insure the structural integrity of the wall.
The existing cracks are from .002" wide to .035" wide and will be injected
but I have a lot of wall left to pour. If any one knows of a good authority
on cast in place concrete for water retention I would be interested.