Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Water Retaining Concrete

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Chance:

Thanks for a detailed reply to my questions.  I note that the cracks are
in vertical direction, the cracks are of uniform thickness across the
wall, and that the wall has not encountered any external loads (because
of the absence of backfill).  Therefore, your conclusion that the cracks
are due to shrinkage appears correct.  The spacing of control joints is
well within what is commonly practised as a good detail.  Also, because
the cracks are of shrinkage origin, 'z' factor is irrelevant.

I am of the opinion that, primarily, poor curing caused the cracks. 
However, the extent of cracking and the width of cracks indicates that
the concrete might have been of poor quality.  Did the supplier provide
lab test results for the design mix?  Also, get tests done on field
samples as recommended in ACI 318 etc. for quality assurance.  In
essence, the combination of poor quality concrete and very inadequate
curing should have caused the problems you have described.  

One other suggestion:  Try to use smaller size rebar at closer spacing
to keep the cracking under control, or you may provide a welded wire
fabric (say 6X6 W1.4XW1.4) near both faces of the wall.  

Please let me know, how te other walls behave as and when they get
constructed.

Rajendran


Chance, Acie P. wrote:
> 
> 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
>