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RE: Crumbling concrete

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I actually had to look back at the photos when you mentioned efflorescence, as I saw none while I was on site. I think you're seeing false color as a result of the on-camera flash combined with the variation in wall texture in the outdoor shot. Efflorescence is a common problem in my area, so I'm familiar with what it usually looks like. I looked for the presence of obvious crystallization, but could find nothing by eye. The white in the last photo looked more like a spilled/cleaned up mess than an evaporate when I was on site.

One of the intriguing aspects is that this is occurring on a wall which is both entirely above grade and under a covered porch on the exterior, as well as the partially below grade walls. There's no telling what type of foundation is below the walls - they may have been placed without a footing. The wall does get moisture, and there is noticable water in the basement during the one or two heaviest rains each year. The back of the lot slopes up probably 10-12 feet in 40-50 feet of run, and part of the basement is on rock (1/2 basement, 1/2 crawlspace), so parts are going to see wetness every big event simply due to volume.

I took a sample, and once I research on the possible causes, will send it off to my local lab to tell me what is in it.



At 08:31 AM 12/23/2004 -0800, you wrote:
Jordan,

This looks like deterioration due to moisture penetration from the exterior.
Look for a not-original moisture source adjacent to the house.  Often it is
a planter that was added adjacent to the house [that does not seem to be the
case here], or a removed roof-gutter-and-downspout system [though I've seen
this a number of times -- the old gutters start to leak and, rather than
repair or replace them, the decision is made to just remove them and let the
water fall from the eaves to the ground next to the house -- that may not be
the case here since there seems to be a downspout-to-drain-pipe system next
to the house].  However, since there is a lot of damage right where two of
the drain pipes enters the ground, perhaps the drain system discharges under
ground next to the house instead of carrying the water away.

It works something like this.  Water from some source enters the wall and
migrates through it.  Salts dissolved into the moisture from the soil, or
from the concrete as the water passes through it, crystallize when the
moisture evaporates into the air in the basement or above grade.  The
crystals form just inside the surface of sound concrete; the crystals grow,
expanding and breaking up the concrete matrix.  The damage is progressive,
working its way into the wall, under the damaged surface, always acting at
the surface of sound concrete.  If you scrape away an area of the damaged
surface, you will eventually come to sound concrete. An indication that what
I've described may actually be the cause would be the presence of
efflorescence [visible accumulations of salt deposits and crystals] on wall
and floor surfaces near the damage.  That may be what is visible in the last
photo and perhaps in the second photo.  Also, since moisture does not
evaporate below grade, the damage probably does not occur more that a few
inches below grade.

Nels Roselund, SE
South San Gabriel, CA
njineer(--nospam--at)att.net

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint(--nospam--at)truesdellengineering.com]
Sent: Thursday, December 23, 2004 6:19 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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