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RE: stamped concrete driveway

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Andrew:
I am not a guru but I think testing the concrete is a waste of time and
recommend you don't rule out a subgrade problem too quickly. This is
probably a deficient design, a structural problem rather than a materials
problem.  7" of plain concrete is typical for a private driveway entrance
off a state highway.  Sounds like you have a much greater traffic volume.  I
recommend some subgrade CBR testing, some shallow borings and some research
into pavement design.  CRSI has pavement design guides and references.

A while ago I worked in an office park where they decided to put a hub for
the busses.  Many bus routes converged on this location, used the ring road
around the office park and all stopped at one bus stop.  Riders could then
make a connection to another route.  The busses tore up the street in a
matter of weeks, the bus stop area, and all the curved sections of the ring
road all quickly deteriorated from the busses braking and turning. They were
going only one way around the ring so only the inside lane fell apart.  It
was asphalt, but it was a great illustration of how critical traffic
assumptions are to pavement design, conveniently it occurred right out the
window of our office.

Jan Harris
Liberty Engineering. PC
Virginia Beach, VA

-----Original Message-----
From: Andrew Kester [mailto:andrew(--nospam--at)baeonline.com]
Sent: Thursday, May 22, 2003 09:56
To: seaint(--nospam--at)seaint.org
Subject: stamped concrete driveway


I have been asked to perform an evaluation of a concrete driveway in front
of a very busy convention center. Heavy traffic, including repeated stopping
and starting of buses occurs. The driveway consists of plain concrete on
what I am assumed is a properly compacted subgrade. There are architectural
details, or stamped concrete (also colored), throughout the driveway. The
drawings I have are limited, but indicate at a regular cross section the
slab thickness = 7". At the areas of stamped concrete the top of slab drops
4", on which a layer of approximately 1" of clean sand was placed, and
finally a 3" layer of concrete was placed. It is this 3" layer that is
stamped and colored to create the look of pavers. They have scored joints to
give it this look, but the depth is unknown and was not specified on the
plans. The Tech Specs do not give any unusual info, it is just regular
3000psi.

The problem is the pavers are cracking and spalling, and some of the regular
concrete (unstamped) is also cracking. But the biggest issue is spalling
along the scored joints of the stamped concrete. Large pieces are coming
loose, and the joints appear to be failing to a point where I believed at
first (w/o seeing the dwgs) that each piece of concrete was a paver. Turns
out, I believe the concrete just failed at the scored joints. I have more or
less ruled out a subbase problem as there appears to be no settlement or
potholes or related settlement. Keep in mind there is a 7" thick slab
beneath the stamped concrete. There is a detail of an expansion joint
between this scored slab and the regular slab, but I do not know if it is in
place or not. I do not think that has much to do with it as the concrete has
some major issues not hairline cracks. Also we are talking about a very
large area with problems throughout, not one truckload of concrete that may
have been bad.

I am going to reccomend some sections of the scored concrete be removed and
tested for compressive strength. Also have some of the regular concrete
cored and tested. Are there other materials type tests that I may have done
that could tell me if there is an aggregate or chemical problem going on? I
plan on being present at the removal to investigate the condition of the
subbase (sand) and the concrete below it. So my natural inclination after
all of this is that it is "bad" concrete...

So do you concrete gurus have any thoughts or has anyone else had problems
with colored or stamped concrete?


Thanks in advance,

Andrew Kester, EI
Longwood, FL

ps
Did everyone read about the devestating earthquake in Algiers? Over 500
people lost their lives. So as much as we complain about our codes and
enforcement, look at how far much of the rest of the world needs to go and
we can be thankful for at least the progress we have made.

The quake registered a magnitude of 6.7 according to the U.S. Geological
Survey's National Earthquake Information Center in Denver, which monitors
seismology worldwide.




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