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RE: Crumbling concrete

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This was, most likely, mixed and placed by hand. The rock and sand were likely collected from the local streambed. There are definitely small bits of wood mixed in (bark, a piece of solid sawn) as well as other items. I'm pretty sure there was the remains of a hand-rolled cigar on one side of the basement, embedded about 1" in from the face of the original wall.

Thanks to everyone who replied with suggestions for testing and possible causes. It gives me some good starting points (and search terms) for when I go to the local Uni library.

Jordan

At 09:41 AM 12/23/2004 -0600, you wrote:
Since it is 100 years old I would consider it may have been site mixed
by hand.  I have been on trips to Mexico and other 3rd world countries
where this is still common today.  The sandy soil is piled up and cement
added and then a bunch of guys attack it with shovels.  Dirt gets mixed
is and the aggregate is not always clean to begin with.  It is placed by
buckets.

Just a thought.

Rich Lewis
Lewis Engineering


-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint(--nospam--at)truesdellengineering.com]
Sent: Thursday, December 23, 2004 8:19 AM
To: seaint(--nospam--at)seaint.org
Subject: Crumbling concrete

I'm curious what would cause older concrete walls to crumble into a
lightweight, easily-friable condition.

Here's my story:

I just went by a 100+/- year old residence yesterday and saw the most
amazing concrete wall deterioration I've ever seen.  Portions of this
mostly-above-ground basement wall (I'm going to say 30-50%) were friable
to
the touch, and easily (literally fell apart) crumbled in my hand.  In
the
soft areas, a masonry bit advanced without significant resistance until
it
hit a large piece of aggregate, usually about 1.5 to 2" into the 9"
thick
wall. My only time reference is that - according to the owner - it
wasn't
present in the 60s when they bought the place.

There is significant evidence that some organics were included in the
mix,
along with sand and round river rocks.  You can see the diagonal
striations
of segregation from where the concrete batch placement started at the
corners and flowed down the walls to its final resting place.  I'm
guessing
that casual water intrusion has slowly decayed the organics to the point

that they have partially disintegrated reducing the strength, with the
remaining organics moisture cycling to break what was left.  There was
no
obvious sign of chemical residue on the surface of the wall.

Interestingly, there is no sign of macro-deterioration of the structure
(yet). No settlement or stress cracks, even where the unbalanced
backfill
is close to 5 feet.  Nonetheless, the walls are going to have to be
replaced.

I'm curious what might be happening, and if there are any tests that
might
be recommended to determine the cause of the damage.  I'm doing this as
a
side research (unbillable) for future reference, as the current owner
just
wants to know how to fix the problem (replace the walls), and the value
of
the house is only about $120k-$130 without the wall issue, and currently

has no historic significance.

If you're curious, there are some photos here:

http://www.truesdellengineering.com/1125/index.html

Thanks, in advance, for any thoughts/suggestions you folks might have,

Jordan



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