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From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <ckxZb.2588$_3.40773@typhoon.sonic.net>
Date: Sat, 21 Feb 2004 00:08:40 GMT

Carl Fogel writes:

>> One example of hard surface coat failure is road striping that
>> causes asphalt pavement cracks large enough to make pieces of
>> pavement to break out and bicyclists to fall.

>> Here is one reference, if you look in the "ANODIZE" paragraph:

http://www.matronics.com/rv-list/hovan/tips/AlAnDef.html

>> Here is a good picture of a failure, never seen before rims were
>> anodized:

http://www.wiredfool.com/2003/06/25/impendingFailure

> Is the road striping harder than the pavement?

It is less elastic and has a tensile strength that particulate asphalt
mix does not.  These stripes are a thick plastic coat (not paint) that
gratuitously act as "wake-up" ribs in bicycle lanes where they are
posted in word and symbol just as thick as lane stripes.

> I had a vague notion that the familiar pavement deterioration under
> the striping was more a corrosion or heat-cycle problem, since it
> often occurs where no traffic rolls over the paint, but I don't know
> what process you have in mind.

> Can you expand a bit on why the stupid road goes to hell under the
> paint? My rims are fine, but the highways around here are terrible.

Well that's what it is.  Thermal pumping of pavement under these thick
stripes cause cracks adjacent to them.  Once a crack is initiated, it
grows with each thermal cycle as the crack fills with fine grit that
cannot escape when pavement shrinks.  This throws up a welt on either
side of the crack while the crack remains essentially unchanged in
width.  Each time the crack expands with the heat of the day it is
again filled with some new grit and resettled old grit.  That is how
the welts at road cracks are generated and what makes concrete slab
pavement "drift" apart.

You'll notice that the ga-bonk-a-bonk on concrete highways is caused
by the ends of slabs curling up.  This is caused by the same thermal
pumping effect that widens cracks in asphalt.

> You also mention this link:

http://www.wiredfool.com/2003/06/25/impendingFailure

> It wasn't loading the pictures of dying rims when I peeked at it,
> but the text left me puzzled. You commented that the failure was
> never seen before rims were anodized, referring as far as I could
> tell the 36-spoke anodized rim that was coming to pieces on the rear
> of a tandem:

>   "...what is the expected result of 36-hole 14 ga spokes, a 390 gm
>   hard anodized ceramic rim with single eyelets used on the rear
>   wheel of a tandem?"

> But the rest of the page is about a similar, but less dramatic
> problem with a non-anodized rim:

>   "I have had single eyelet Mavic rims do something similar to this
>   on my road bike, but that was with the old MA rims. They were made
>   out of a softer metal, not hard anodized, with a much more square
>   profile. That rim just pulled a small section of the inner box
>   wall out in a rather slow, progressive failure. This one seemed a
>   little more dramatic."

You'll notice that the rim did not have sockets.  That is often a
worse failing than anodizing as in the Mavic MA-3.  This one however,
had nothing to do with whether or not the rim had sockets.

> Isn't the fellow saying that he had in fact seen the same kind
> of failure with an older non-anodized Mavic single-eyelet rim on
> his road bike, just less dramatic than on his anodized Mavic
> single-eyelet rim on a presumably more heavily laden tandem?

No he didn't say that.  He said the spokes pulled out.  Failures such
as the one pictured, when not noticed, have led to separation of the
rim so that the tire was on the outer part and the spokes on the
inner, the wall thickness of the box section being thinner than the
braking wall.  I'm not sure what the rim in the picture would have
done.

To get a better appreciation of the forces involved, try:

http://draco.acs.uci.edu/rbfaq/FAQ/8b.25.html

Oh!  And don't miss reading this item that affects all of us,
bicyclists or not:

http://www.utexas.edu/admin/utpd/atm.html

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <ENAZb.2640$_3.41300@typhoon.sonic.net>
Date: Sat, 21 Feb 2004 04:04:52 GMT

Tom Sherman writes:

>> You'll notice that the ga-bonk-a-bonk on concrete highways is
>> caused by the ends of slabs curling up.  This is caused by the same
>> thermal pumping effect that widens cracks in asphalt....

> Permanent concave upward curling of Portland cement concrete slabs
> is primarily due to differential curing. Temporary deformation will
> also occur if there is a temperature gradient within the slab.

How does this occur years after the concrete was poured and grow in
amplitude with use if it is a curing problem, a problem found around
in the USA and Europe for concrete highways.

If this were a load related event, then joints should be sinking below
average as railroad track classically does at rail joints.  In
contrast is an upward distortion at the crack and it occurs on asphalt
as well as concrete only that with asphalt it is more localized to the
fissure, asphalt pavement having less bending strength.

> Poor ride comfort over crack control joints is the typically the
> result of inadequate load transfer between the slab sections that
> results in slab faulting.  The impact of wheel loads on the edge of
> the slab causes pumping of water which carries the fines (particles
> smaller than 0.075-mm) in the subgrade soils forwards under the
> slab.  The slab faults (tilts) so small drop-offs occur in the
> direction of traffic.  [1] These can easily by seen by visual
> observation.  These is one of the reasons why fine-grained soils are
> classified as "fair to poor" subgrade materials.

I don't see how you correlate that with cracks in roads rising.
Besides, this type of crack elevation occurs even on the best
sub-grades that are well drained.  This pumping action is more
apparent on curves where curved segment of a concrete road "wander"
away from the curve, there being no retention as they pump apart day
after day.  I have seen curbs and curve segments of pavement with
three to five inch gaps even where no significant traffic passes other
than pedestrians and bicycles.

> [1] Pre-WW2 Portland cement concrete faulted slabs in Sweden were
> observed to level out and then fault in the opposite direction after
> the war when traffic direction was reversed.

Well the lumps we get here and in central Europe are symmetric about
the joint.  Again, how do you explain that asphalt roads act
similarly?

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <T4BZb.2645$_3.41405@typhoon.sonic.net>
Date: Sat, 21 Feb 2004 04:25:23 GMT

anonymous snipes:

>> Poor ride comfort over crack control joints...

> These are expansion joints. Control joints are typically found on
> sidewalks and other pedestrian surfaces.  Ride comfort is the least
> of our worries when it comes to expansion joints.

I take it you have never met a real expansion joint on a bridge.  The
ones on larger bridges eat bicycle wheels whole.

>> ...is typically the result of inadequate load transfer between the
>> slab sections that results in slab faulting.

> Many of these slabs are not flush with their neighboring slabs from
> the first moment of their creation.

These are continuous pour, machine leveled highways.  The cracks are
sawed in after the concrete is cured to prevent random jagged cracks.
In fact the cuts do not even go entirely through the slab and rely on
thermal stress to make the final separation.  It is at this point that
thermal pumping introduces fine silt that cannot be ejected from the
crack when the road is heated by sunlight but can fill the crack when
the concrete shrinks.

>> [1] Pre-WW2 Portland cement concrete faulted slabs in Sweden were
>> observed to level out and then fault in the opposite direction
>> after the war when traffic direction was reversed.

> Interesting (seriously). What is the cite?

I don't believe a word of it having seen no difference on motorways in
England than here.  The raised slab ends are ubiquitous.

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <38UZb.2823$_3.44338@typhoon.sonic.net>
Date: Sun, 22 Feb 2004 02:05:51 GMT

Rick Onanian writes:

>>> I take it you have never met a real expansion joint on a bridge.
>>> The ones on larger bridges eat bicycle wheels whole.

>> Expansion joints are much more insidious when they are parallel to
>> the rider's travel direction. A skilled cyclist need not be too
>> concerned with crossing expansion joints at right angles, while
>> longitudinal cracks cause nasty displacement wrecks on a regular
>> basis.

> What kind of expansion joints do you have? Maybe like this:

http://wbacorp.com/images/bridge_samples/silicone-crete_install.jpg

As you see, this guy is blowing the grit out of the crack so that it
will not pump farther apart, and then it is filled with a relatively
spongy tar mixture that is supposed to prevent intrusion of sand.
Water is not the main effort here.

> Here, we have joints with 2 to 3 inch long interlocking teeth. The
> joint is generally placed at a angle that is 5 or 10 degrees from
> perpendicular. The teeth, diagonally cut, then end up with one side
> of each tooth parallel to the road, and the other side a good 30
> degrees from parallel.

These are not a hazard except for wet traction.  The Golden Gate and
other large bridges have 24-36 inch long two inch wide curved beams
that interleave.  You can ride down one of these into the slot and cut
the wheel off just below the hub.  Don't do it!  When I encounter such
a device I take a slightly angular path across it.  In the wet, all
bets are off.  It's hopeless.

> Disclaimer: All numbers above pulled out of my ass for demonstrative
> purposes.  The mind-image I've created may resemble reality.

> They tend to have one side sticking up, so the edges of the teeth
> are often pointing up into traffic as if intended to pierce tires.

> Mine look kind of like:

http://www.pipingtech.com/products/expjtcat/extern23.jpg

> and, as I said, are installed off-kilter.

> The result could be disaster for an inattentive cyclist. It pays to
> pay attention to the road surface.

>> Interesting.  Around these parts the Portland cement road sections
>> are created one slab at a time with substantial separations between
>> slabs,

> We don't have concrete roads around here; all asphalt.  There's an
> existing highway, Interstate 495, that has some concrete mileage
> right were I-95 meets it in southern Massachusetts; it's currently
> being replaced with asphalt.

> I understand concrete is a longer-lasting road surface, but rather
> expensive to install, and of course, inconvenient. Is that a correct
> assessment?

I don't understand why we have concrete roads at all except that they
last longer while giving horrible service as they bounce traffic
ga-bonk-ga-bonk... along. Interstate 280, a relatively new 10 lane
concrete freeway in the SF Bay Area was recently planarized with
diamond cutters, a device much like the saws used to cut "rain
grooves" in roads.  That was a huge expense.

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <KGUZb.2839$_3.44408@typhoon.sonic.net>
Date: Sun, 22 Feb 2004 02:42:50 GMT

Carl Fogel writes:

> Much of the asphalt bicycle trail on the Arkansas River has been
> replaced with concrete. The old asphalt trail had a bad habit of
> surrendering to tree roots and cracking.  The newer concrete
> sections are noticeably faster, having a smoother surface to start
> with and not breaking up like the asphalt. (I just started riding
> the recently re-paved section again and have to use my brakes now on
> a familiar turn.)

> Older stretches of the concrete trail seem to be lasting fairly
> well, just as concrete stretches of I-25 near Denver tended to
> outlast asphalt further south.

In my city, street trees are ubiquitous, causing upheavals from their
roots that damage concrete streets and sidewalks as much as asphalt
paved ones.  In fact sloping and mismatched concrete slabs are a major
problem for the street department that puts in asphalt transitions so
that people don't trip on sidewalks and cars don't ding rims on the
streets.

> Unfortunately, apart from the initial expense, concrete is a beast
> to replace when it finally goes to hell.

They both break up nicely with a large bucket loader as it scoops up
the sections directly into dump trucks that haul it away.  Recently,
this material has been crushed and re-used as aggregate for asphalt
pavement.

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <ASTZb.2812$_3.44108@typhoon.sonic.net>
Date: Sun, 22 Feb 2004 01:47:12 GMT

Robert H? writes:

>> I take it you have never met a real expansion joint on a bridge.
>> The ones on larger bridges eat bicycle wheels whole.

> Expansion joints are much more insidious when they are parallel to
> the rider's travel direction.  A skilled cyclist need not be too
> concerned with crossing expansion joints at right angles, while
> longitudinal cracks cause nasty displacement wrecks on a regular
> basis.

Not so.  Those old fashioned gaps come from individual pouring of slabs
and represent the form board end before the board is removes and the
next slab poured.  What is left between the slabs is a fiber pad that
is covered with sealant, primarily to keep sand and grit out.  Of
course this never worked so today concrete is poured continuously and
sawed.  There is no need for expansion joints because concrete expands
about the same as the surface of the earth and is elastic enough to
absorb transient thermal expansion.  It's the shrinkage that is the
culprit, concrete not having any significant tensile strength.

>> These are continuous pour, machine leveled highways.  The cracks
>> are sawed in after the concrete is cured to prevent random jagged
>> cracks.  In fact the cuts do not even go entirely through the slab
>> and rely on thermal stress to make the final separation.

> Interesting.  Around these parts the Portland cement road sections
> are created one slab at a time with substantial separations between
> slabs, all the way down to the base layer.  The joints are topped
> with sealant in a vain attempt to keep the moisture out.  What you
> are describing is a control joint.  Control joints are created to
> dictate, theoretically, where the slab will crack.  Expansion joints
> exist to keep a slab from cracking at all.  Expansion joints are
> particularly evident when you're bolting down the runway in that 747
> on the way to another Euro cycling adventure: bump, bump, bump,
> bump...

By the way, these roads are made of concrete that is a mixture of
cement, sand and gravel.  That they crack from thermal shrink is
understood and that is the reason for cracks that one would rather
have at predictable intervals rather than random or bunched probably
at the weakest cross section.

>> It is at this point that thermal pumping introduces fine silt that
>> cannot be ejected from the crack when the road is heated by
>> sunlight but can fill the crack when the concrete shrinks.

> The freeze-thaw cycle is a much more brutal destroyer of pavement
> structures than silt pumping.

Call it what you want, thermal pumping works equally well in summer as
in winter.  It is crack filling with incompressible debris that
damages pavement, be that asphalt or concrete.

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims suck?
Newsgroups: rec.bicycles.tech
Message-ID: <b5a_b.3035$_3.48086@typhoon.sonic.net>
Date: Sun, 22 Feb 2004 22:31:35 GMT

Robert H? writes:

>> Those old fashioned gaps come from individual pouring of slabs and
>> represent the form board end before the board is removes and the
>> next slab poured.  What is left between the slabs is a fiber pad
>> that is covered with sealant, primarily to keep sand and grit out.
>> Of course this never worked so today concrete is poured
>> continuously and sawed.  There is no need for expansion joints
>> because concrete expands about the same as the surface of the earth
>> and is elastic enough to absorb transient thermal expansion.  It's
>> the shrinkage that is the culprit, concrete not having any
>> significant tensile strength.

> Well you are part right.  It is true that modern rigid pavement
> construction involves as little human involvement as possible, with
> the PCC spread, leveled and vibrated by machine.  But this does not
> mean there are no formed joints.

Today, concrete pavement is poured with re-usable steel forms that are
moved and reused as soon as the slab has cured.  In dry weather,
sprinklers and covers are used to prevent surface cracking and loss of
moisture needed for strength in curing (re-hydrating cement).  For
this reason, transverse joints are minimized but the subsequent saw
cuts, in time, present the same problem as joints because thermal
expansion and contraction pumps grit into the joints.

> In fact there are still plenty of forms involved because it is
> usually impossible to lay a PCC structure in one fell swoop.  In
> reality, the street is constructed in sections, as usually a lane at
> a time is constructed, and the crew stops work at lunch and the end
> of the day, etcetera.  While the openings left by these forms could
> properly be called "construction joints," they nonetheless function
> perfectly as expansion joints and contraction joints.  In their
> absence, control joints must be sawed in at 15-foot intervals and
> longitudinally between lanes.

The following web site refers to silt intrusion into cracks. the
cause of raised ends at joints/cracks on concrete and asphalt pavement:

http://www.pwmag.com/articles/online_articles/joint.htm

> Longitudinal joints of various types are ubiquitous on new PCC
> roadways and are of much more concern to cyclists than transverse
> joints.

Please don't introduce any more red herrings.  The initial subject at
hand was bumps in the road not the why and how concrete is poured.

Jobst Brandt
jobst.brandt@stanfordalumni.org

 






































































































































































































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