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RE: Water Retaining Concrete

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Acie,

Cracks in the vertical direction indicate that the problem is as you
originally stated, shrinkage.  The "z" calculation is therefor irrelevant.  

I still would be interested in the control joint detail.  Was the wall
scored with a v formed joint, and was the rebar discontinuous at the joints?
I have seen cracks parallel the intended joint due to this very issue.  The
other issue is the amount of horizontal rebar, which I still feel is too
little.

Re: Handbook of Concrete Engineering, by Mark Fintel, p. 668, 18.2.3
Reinforcement for Shrinkage.  Also look at figure 18-5 for examples of good
joint details including a control joint.

The use of flyash appears appropriate, because it reduces heat of hydration
which can help mitigate the sins of poor curing practices.

Good curing allows the concrete to gain sufficient strength prior to
significant shrinkage.  Once the concrete has sufficient strength the self
forming shrinkage cracks will be more distributed, and smaller in width.
The smaller width cracks will not have the same tendency to leak.

One other measure that can exacerbate cracks is gap graded aggregate.  It
will still meet C33, but aggregate can be the single biggest contributor to
shrinkage.

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


-----Original Message-----
From: Chance, Acie P. [mailto:acie_chance(--nospam--at)wdi.disney.com]
Sent: Saturday, October 03, 1998 8:51 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: Water Retaining Concrete



Rajendran

First I want to say thanks for the help. Second you must not sleep, much
5:00 AM ? The answers to your questions follows.

1.) Cracks are in the vertical direction.
2.) Some of the control joints cracked however there were also cracks 6"
away from the control joints through the tie holes. There were on the
average two additional cracks between the control joints which were at 25
ft. O/C.
3.) We only measured the cracks at the surfaces. The cracks were about the
same on both sides.
4.) The first wall was cured very badly. The forms were striped after one
day and vinyl backed burlap hung over the wall. The wall was not kept wet.
There were many times the inspector, other engineers and my self found the
burlap dry. The burlap was remover after seven days. This wall will be water
proofed with a membrane type water proofing material. The first wall was
placed in the second week of Aug. with the very high temps. The second wall
was cured according to specifications. The forms were loosened on the next
day and left in place for four days with a soaker hose on the top of the
wall to keep the forms wet. On the fourth day the forms were striped and
good vinyl backed burlap sheets were hung with a automatic sprinkler setup
for keeping the wall wet. The contractor was cooperative on the second wall
as we will bill him for the rework on the first wall. The cracks in the
second wall were not as sever as the first however there were two to three
thin cracks in each segment of the wall which runs about 20 ft. then made a
45 deg. turn. There are four of these dog legs in the second wall. No
control joints were used in the second wall because of the dog legs.
5.) No backfill was place before the cracks were found.
6.) No tests were done on the concrete after the wall was poured.
7.) We used water-reducing admixtures as recommended in ACI 650 sect. 3.2.
The water-reducing admixture and flyash were added to increase the density
of the concrete.
8.) We did use a Air Entrainment admix also. The test at the time of pouring
were about 4%.
9.) The second wall was a battened wall two ft. at the bottom and one ft. at
the top. The cracks were at the bottom and died out as they went to the top
on the second wall. Rebar was the same as the first wall.

If you or other members of the list want we can continue this off the
server. My E-Mail address is Acie_Chance(--nospam--at)wdi.disney.com

Thanks
Acie Chance