Poor design led to I-35W bridge collapse?

Thank you for taking this time to teach me!


I had no idea cement can be cored. What kind of drill do you need? Does it need diamond edging?

ARe the forms for those cylinders laying down or are they upright? Does it make a difference which way they lie?

Oh!!!!
Now I understand. It appears that everything having to do with the Big Dig was put into "hurry it up" mode. So they^WThey used things that dried fast. The only company to get its hand slapped (so far) in the tunnel ceiling failures is the company that provided the glue to stick the cement slabs to the ceiling. It was a fast drying epoxy and the company has stated that they sent memoes warning about using the quick-drying materials.
The same thing must have been done with the cement that was (according to the news) supposed to make the various tunnels water proof.

OK. I may have leapt to the wrong conclusion but now some things are making sense to me. THANK YOU VERY MUCH!!!

I've just tripped over more stuff that I didn't know I didn't know. Kewl! Unfortunately, I don't not-know enough to ask questions.

I have a hypothesis. The brother-in-law who had this job never showed up for work. That seems to be SOP in this state.

And I'm sure we won't hear about it in the local news.

MIT kept sending students to observe the construction over the 15-20 years it was getting done. Would these "newbies" know enough to look for them?...and look at them?

Does every concrete piece of a project have these sample cores stored somewhere in the world in perpetuity?
/BAH
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snipped-for-privacy@aol.com wrote:

I guess you missed this when I wrote about it a few posts back.

A core drill with an abrasive edge.

Most do though there are those with carbide. One of the partnered businesses I started refurbishes spent core drills by brazing new diamond segments to the spent drill. We currently refurbish from 2 through 24 inch units.
<snip>
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wrote:

A favorite method of examining rock remanent magnetism, in connection with geomagnetic reversal research, is to use a one inch or two inch core sampler, having marked the compass orientation and slope of the sample. The read out takes a sensitive magnetometer, and sometimes a bakeout.
Brian Whatcott Altus OK
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<snip>

I've been side-tracked this week. A brand new septic tank system is going in and it's been very busy here. Sorry. I have to watch how they do this work! I'm having a ball. :-)

I need to learn what that means.

Oh, boy! There's another piece of knowledge I don't know anything about. I can't imagine how you would attach a diamond to a metal thingie.
/BAH
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snipped-for-privacy@aol.com wrote:

Tiny industrial diamonds are embedded in a soft iron slug shaped and sized to fit a straight sided mild steel barrel. The flat surfaces, on one edge of the diamond bearing slug, the other the working end of the barrel, are brazed together. The temperature for this operation is lower than the destruct temperature of the diamonds.
The back end of the barrel has a large nut welded to it that attaches to a motor that turns the barrel. The mounting, and the motor shaft, have a hole that allows cooling water to be continuously introduced during the core drilling operation.
During core drilling, the trick is to have the soft iron slug wear away at the right rate to expose the tiny pieces of diamond which is what do the actual cutting. At the micro level the process gets ever more complicated, but eventually the slug that contains the diamonds wears away and needs to be replaced.
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To make the slug mix do you need a foundry?

I think I can see it. Thanks! :-)
/BAH
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snipped-for-privacy@aol.com wrote:

Not a very large one. The slugs on core drills have a variety of hardnesses based on customer preference. At the slug manufacturing level you'll buy that material made to spec by the full scale foundry, and remelt to manufacture the slug containing diamonds based on anticipated orders.
I buy the slugs (more frequently called segments) made to the sizes for the batch waiting to be refurbished. I order from a California firm with their product generally in my hands within 7 days, sometimes in 3.
The segment manufacturing process must be interesting because the last few thousandths of an inch along the edge that gets attached to the core drill barrel has no diamonds in it. The rest of the segment, along with the other three surfaces not only have diamonds, but they're already protruding slightly, ready for use.

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On Aug 28, 7:21 am, snipped-for-privacy@aol.com wrote:
...

Just to throw out a common jab that folks in the ready-mix industry do, cement isn't cored, concrete is cored. Cement is a component of concrete. Cement is a powder, Concrete gets hard.
To get any life out of anything used to cut concrete, they almost always have a diamond impregnated cutting edge. Expansion joints in concrete driveways are often cut with diamond edged saw blades. Both saws and drills almost always use water as a coolant during cutting.

Test cylinders are a round cylindrical shape and the manner in which the material is collected and tested is specified by the ASTM. Here is a guide on how this is done from the National Ready-Mix Concrete Association. http://www.nrmca.org/aboutconcrete/cips/34p.pdf
...

Test cylinders are almost aways destroyed in testing. Thus they don't hang around. The testing that will take place is dictated by the Contractor, Architect, Engineer, and often Concrete Producer.
The Contractor et al, will want them to validate the designed strength is met allowing them to avoid taking core samples. The Concrete Producer will make the samples if they are trying to validate a mix design or design change.
Note that in nearly every case, when discussing the "strength" of concrete, we are discussing the "compressive" strength of the material. Basically how well it resists crushing.
If there are any cylinders still around after 28 days, it is because one cylinder was found to have not met the spec after 28 days. Thus the engineering group has decided to test again after another 28 days to verify that the engineered strength will eventually be met. This can happen on a pour if environmental, or issues at the plant cause a slight mix change that isn't noted. Baring any significant problem, the concrete will eventually cure.
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Mike H wrote:

That's not true. Expansion joints are poured in with a compressible material filling the joint. What you're talking about is scoring that's put in after the concrete is poured and partly set. The score lines have the purpose of giving future cracking someplace specific to go.
> Both

Yes.
snip
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...
You are correct, I used an incorrect term. The joints cut into the concrete are called "control joints" and are used to promote cracking in a specific location. Expansion joints are as you stated, gaps filled with a compressible material. Such joints are necessary wherever a slab comes in contact with another object (another slab, a wall, a curb) otherwise the expansion of the slab when heated could push against things and either move them, or crack the concrete.
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Mike H wrote:

Thanks. Happens to all of us.
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Oh, I've been screwing up my word usage again. Thanks for the correction. I suspect you are going to have to hit me over the head sometime in the future w.r.t. this one because I have a feeling I've been mixing the two up all my life. The correction will be welcomed. :-)

Does concrete burn?

Do you have to alter recipes from one batch to the next batch to get the same strength?

Yea, I assumed that.

I think you just answered the above question.
/BAH
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On Sep 2, 5:35 am, snipped-for-privacy@aol.com wrote:
...

The aggregates in concrete do not burn unless some special man made aggregate is used. High heats from a fire could damage the reinforcing steel in the concrete, or any fasteners attached to the concrete thus leading to a structural failure. http://www.concretecentre.com/main.asp?paged9
...

Lets say a typical concrete plant in a typical city when busy can product over 3500 cubic yards of concrete per day. (Central Mix plant) Estimating, 4000 psi concrete (typical driveway, residential concrete mix) takes about 6 bags of cement per cubic yard at 80lbs of cement per bag. That works out to about 140 tons of cement per day. Cement is hauled in on Rail or most often on Truck directly from the cement manufacturer who rails it into their depo. Most concrete plants will have two or more silos that allow them to store between 30 and 80 tons of cement at a time. These silos feed the plant. The trucks feed the silos.
Now you will also need 3280 tons of Sand, and 3220 tons of rock.
Now consider the volume of that moving through a plant and the variations that can occur. Batches of cement coming out of the kiln will have slightly different properties. These properties are documented on a sheet that comes from the cement producer with each truck load. Moisture content is the biggest issue with aggregates so moistures are checked regularly through the day to identify the moisture content of the material that is flowing over the scale. (Some plants have moisture meters at the feed belt to the scale and can measure it on the fly) All of these details of the components are maintained inside the batch computer that then uses that information, plus the engineered mix design, to tweak the mix. Then you add on top of that a batch plant operator that is aware of the current atmosphere conditions, traffic, conditions on the job site (radios) and on job performance, and he may tweak things a bit as well.
So yes, depending on moisture you may need to adjust things from one batch to the next to maintain strength, though generally the changes made are more related to other performance characteristics. Things like workability and set time.
One side note that is kind of interesting. When pouring a tunnel and runway for the international airport, a local Ready-Mix provider had to come up with a way to place the 12" thick concrete pads while preventing issues with rapid curing and high heat generation creating cracks in the concrete as it cured. Their solution was to replace much of the water in the mix with liquid nitrogen. They rigged up an injector system that allowed a truck to back up to it, and the injector would inject liquid nitrogen into the concrete mix. This would then be mixed up and discharged into the pad. They only cracked the drum on two ready-mix trucks before they had things tweaked just right.
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Mike H wrote:

[snip]
Concrete does not burn, as such, but heat will damage concrete.
CaCO3 + heat ---> CaO + CO2
Olin Perry Norton
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wrote:

Converting it back to cement powder?
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Yep.
I have seen a concrete freeway after a fuel tanker burned. The fire department decided to contain it instead of fight it and then deal with a bunch of hot diesel and gasonline (cleanup and reignition danger). 9000 gallons of fuel burned in about 8 hours. When they were done, there was a bunch of aggrigate, melted steel. No sign of the original roadway surface.
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Not really. It is called spalling and is documented.
http://www.concretecentre.com/main.asp?pagef0
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Dear Mike H:
wrote: ...

Concrete is also hygroscopic. High heating rates can cause water to be evolved, and turned to steam... spalling concrete in the process.
I was familiar with a 12 million curie Co-60 irradiator in El Paso, that had a 1" thick steel plate installed inside the containment area, and air constantly blown through space between the steel and the concrete shell, to keep this from happening to its concrete shell.
David A. Smith
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Say what?!? Unless you're keeping liquid nitrogen under pressure or in a flask, it's going to turn to gas quite readily and quickly. It is doubtful that cement will do its chemical reaction with nitrogen and the aggregate to form concrete.

Perhaps the story is a bit garbled and the aggregate and cement were cooled with liquid nitrogen before the water was added to the mix. Adding liquid nitrogen in any substantial quantity after the water has been added will result in one big ice cube (which won't mix well).
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On Sep 6, 10:08 am, snipped-for-privacy@mojaveg.lsan.mdsg-pacwest.com (Everett M. Greene) wrote:

It's what they did. And it worked. It is becoming more common and not shockingly is promoted by the companies generating the liquid nitrogen. http://www.us.lindegas.com/international/web/lg/us/likelgus30.nsf/docbyalias/ind_conc
http://www.concreteconstructiononline.com/industry-news.asp?sectionIDq5&articleIDU8651
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