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Re: Crumbling concrete

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Jordan,

To find the root cause you would want to take some core samples and send them to testing laboratory experienced with doing petrographic examination per ASTM C856.  Realize that ASTM C856 is a collection of many types of test and they need to be narrowed down to your specific problem.  Along with the cores you would also want to include as much other information as possible such as photographs and as much history as you can similar to what you have shown below.  The obvious tests they would run would be sulfates, chlorides if there is rebar involved, carbonation, pH, and aggregate ASR.  Also specify that you want a final report that includes all the results of the tests and the petrographer's opinion to the cause of the deterioration.

Since there does not appear to be a rebar corroding problem, my guess would be either a break down due to freeze/thaw or sulphate attack.

Thomas Hunt, S.E.
ABS Consulting



"Jordan Truesdell, PE" <seaint(--nospam--at)truesdellengineering.com>

12/23/2004 06:18 AM

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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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