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Re: Concrete Problems

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     It sounds like there is a chemical reaction that produces gasses which
flow upward through the center of the piers.  Equilibrium of pressure with
depth would leave a conic void.  I would also look for segregation in the
shafts of the piers where the gas flowed up through.  What is causing the
chemical reaction?  The water in the holding pond?  Is the heat of hydration
a catalyst? Something in the soil, mix or rebar?  If there was "mud" on top,
then the reaction carried it there.

Just some thoughts,
Greg


-----Original Message-----
From: Brian K. Smith <smitheng(--nospam--at)dos.net>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Monday, January 24, 2000 8:42 AM
Subject: Concrete Problems


>I have an interesting problem I need some assistance with.  The background
>data goes something like this:
>
>The project is a multistory hotel with block and plank construction.  The
>soils dictated the need for drilled pier support with structurally
suspended
>(void box construction) grade beams.  Wind speed 70mph, zone 0.  The piers
>are currently in place as well as the grade beams.
>
>Prior to pouring the grade beams, the testing agency made an inspection of
>the project and noted "mud" on top of the piers.  The inspector then had to
>go "down the hill" to inspect some steel in a detention pond prior to
>concrete placement.  By the time he made it back "up the hill," the
>contractor had already placed concrete on the piers, without a second
>inspection.
>
>The Owner/contractor (as expected) indicated that all of the piers had been
>cleaned prior to concrete placement.  They said they had an affidavit from
>the individual who did the work.  I told them to send me the affidavit
>(notarized) and by the way, go ahead and dig up two piers and let the
>inspector check them.  After excavation and power washing, both of the
piers
>had conical voids of varying size, between the piers and the grade beams.
I
>selected another 10 or 15 piers to excavate, clean, and inspect.  The
>majority of these piers also had conical shaped voids of varying size.  In
>several locations, I could see (from pictures provided by Owner/contractor)
>the vertical rebar in the piers as well as some of the pier stirrups.
>
>The Owner called and asked, "What do you think?"  I told him he better go
>ahead and excavate all of the pier/grade beam intersections, clean them,
and
>have them photographed and inspected.
>
>My dilemma now is how do I fix this problem.  My thoughts are to excavate
>below the grade beam, support the beams if necessary, and demo about 12 or
>24 inches of the pier, clean the rebar, split a sonotube and reform the
>pier, and pour back with a flowable high strength concrete.  Am I missing
>anything?
>
>Brian K. Smith, P.E.
>
>