The 9/11 Forum

[SanderO]

Whitey...

Can someone brilliant such as yourself... calculate or show me where the calculation is... for how much heat would be released in the mechanical crushing/pulverization of a ton of concrete or any unit of concrete?

I know it takes energy to mechanically destroy... but there is also heat released... Can you help me?

[OneWhiteEye]

Well, my good man, when I search for the keywords in your query, where does it lead me? To this forum.

Start here - http://the911forum.freeforums.org/henry-couannier-vs-greening-concrete-pulverization-calcs-t298.html - this is where I'm going to start. I'll see what I can pull out of it.

[OneWhiteEye]

A quick and dirty answer from Dr. G in that thread:

An analysis of the data presented in the studies by Hughes, Mindess and Bischoff noted above shows that the impact energies actually employed in their studies of concrete utilized about 1000 joules to fragment a 10 cm block of concrete into 1 cm, or smaller, cubes, in which case the fragmentation process actually used only about 5.4 % of the available energy. This suggests that impact fragmentation is not a very efficient process.

Bear in mind there are dependencies on impact energy, sample geometry, sample size, degree of confinement and final particle distribution size (as well as other factors). If one takes the approximately 5% figure to be exemplary, then about 95% of the impact energy is left over after fracture.

It's not valid to assume all the remainder goes into thermal energy as a significant portion will remain as projectile kinetic energy (though depending on confinement, further recrushing could rapidly dissipate energy into additional fracture and heat). The coefficient of restitution of most rigid materials varies between 0.6 and 0.8, with the low side being much more typical. This characterizes the energy losses to inelastic response in terms of fractional residual velocity following collision - for bodies which do not fracture. Fracture obviously decreases this value somewhat, but I'd expect a first order approximation is given by subtracting the 5% fracture loss first, then applying the restitution. How good that approximation is is questionable, and it would only apply to a given collision. Repeated collision and mechanical crushing would require repeated application of the fraction, i.e. a pi product over the number of collisions to final particle size.

Need to think about it some more.

[OneWhiteEye]

Needless to say, there's a significant difference in efficiency between impact crushing and confined mechanical grinding, and the temperature of the medium at any point depends on the rate of thermal energy production (power) versus the rate of dissipation to the environment. A slow grind remains closer to equilibrium temperature with the environment.

[SanderO]

Whitey,
I know this is not a pub topic... but the heat post collapse seems to be both largely misunderstood (the amount and origin) and a finger print for incendiaries etc.. high energy devices used to CD the towers. Please move this to whatever thread it needs to be or trash it if it is inappropriate.

Having sanded wood, drilled steel and so forth I know that destroying these material mechanically produces heat... lots of it in the case of drilling steel. But lots is not a value is it?

I believe that the heat produced by the mechanical destruction of the concrete and perhaps other materials may have been responsible for several observed phenomena and I would like to be able to quantity the amount of heat produced (a range?)

I suspect the heat from the mech destruction of the concrete etc.:

heated the air and caused the huge billowing (hot dust clouds which appeared post collapse in all three towers.

caused the creation of things like the *meteor* steel concrete and all sorts of building materials *glued* together into some sort of rock

perhaps created some of the metal micro spheres

perhaps kicked off some unusual.. even exothermic (thermite like) reactions in the fine ground materials from the mechanical destruction... water, aluminum, sulfur, iron... heat

remained in the debris pile post collapse for weeks and months - a huge heat sink.

In communicating with truthers the heat and the amount of dust is what they can't understand.. or attribute the explosive as the only possible cause. The creation of so much heat and such complete grinding of everything may be understandable by physicists but not the layman... they are expecting to see body parts, telephones and file cabinets... not to mention slabs if it was *just a collapse*.

I find myself in a strange position communicating with my truther *friends* because I claim a lot of the NIST work was wrong... but the truther explanations are also wrong. Truthers see my critique as support for NIST... and they can't wrap their minds around a third possibility (let alone a forth).

In trying to understand why NIST got stuff wrong... I find it hard to believe that they just made honest mistakes. They had scores of engineers and so forth... how could they all get some basic stuff wrong? And why did they take so long to get it wrong? Was that because they were hunting around for some model to fit to their (or some pre determined outcome)? That is to say... office fires can collapse steel buildings... such as Bldg 7.

I don't think they can. I don't think they can be hot enough or there is sufficient fuel to burn long enough to weaken enough steel for it to buckle. Therefore I think, if there was heat weakening leading to loss of strength and buckling of steel another mechanism was in play.

I suspect it was related to the diesel fuel...and to the few trusses and cantilever girders which failed. A truss which loses one chord or diagonal member/panel is a goner. If the truss goes it would rapidly spread and the core above would be without support and drop and go right through the Con Ed substation with little to no resistance - column to column alignments for 8 floors... from the top of the mech floor 7 to the ground... the precise distance to explain the 100 feet of free fall descent.

So why... if this is true... or even if it's an hypothesis for consideration...did NIST not go there? I suspect it goes to the flaws in the decisions related to:

building a tower above the sub station
the tower required transfer trusses because there was no direct load path to the foundations
an OOS system was used to get as many of the columns *out of* the substation
placing diesel day tanks above the sub station with a 20,000 tank to replenish the day tanks below .. ground floor or basement which ran on back up power.

What the designers and developers essentially created was a ticking time bomb... if... if some conditions presented...

the sub station explodes (they do.. transformers from time to time from faults or voltage spikes/ shorts and so forth)
The huge sub station transformers contain flammable insulating oil which also... I believe can release explosive gas... which I suppose it what exploded. ... Ask Hess and read Barry Jennings testimony.
placed the transfer trusses...no design choice above the sub station passing through the mech floors ... no interference with office uses by the diagonals etc... stick em in the mech floors.
huge ventilation grilles for the HVAC system and to provide combustion air for the back up generators.. lots of fresh oxygen required for combustion.. dampers to cut off the air supply? Not part of the design I'd bet.
The core was supported by 3 transfer trusses and the north columns by cantilever girders all located on the mech floors 6&7.
If the power was lost the sprinkers wouldn't work
If a water main was destroyed they sprinklers could not be replenished either
Access to the tower was through or adjacent to the sub station... lovely!

I also suspect that their explanation of truss failure at the twins was the same sort of strategy to avoid the fact that the floor system could collapse progressively (easily) and bring the entire tower down

This is all to say that NIST seems to have come up with explanation(s) to avoid the real causes and who might have been involved in them... regardless of whether planes flew into the towers or not... those towers were dumbass structural designs. And of course all the professional groups went silent to protect their buds. PANYNJ was mum because they were the drivers behind the boondoggle... And the engineers and architects made a big deal that the towers were not knocked down by a plane strike... whoopie!

just sayin...

[OneWhiteEye]

Yes, it sems a most worthwhile topic. Soon to have its own thread.

[OneWhiteEye]

These folks might be able to give you a direct answer to your question:

http://asdi.curtin.edu.au/csrp/projects/2b7.html

They've done the work to assess the temperature change in samples (of rock) undergoing pulverization. From what I read at this page and others, there seems to be no reliable analytical means to determine the answer. Physical experiment required.

Other interesting things:

Basic Comminution Concepts

Page with studies including the above

Mineral Processing Technology (Willis)

[SanderO]

OK...

That seems odd... but let say you drill a X diameter hole in material Y... z inches deep.. we can compute the volume of the material destroyed by the drilling... even I can do that... We can also meter the electricity used to run the drill.. measure the heat change in the motor itself and in the shavings and the region around the hole. That is an experiment I can conceive of in my mind and maybe could do in a lab environment.

I know the metal shavings are damn hot! I don't see why concrete would be much different... but that would depend on the matrix which holds it together. Fibreglass gets hot too.

One would think that it's possible to come up with a range of heat released with some quickie math (the kind I can't do). It seems that if 100,000 tons of concrete is *dustified* to use their term...mechanically... you would have a hell of a lot of heat produced... No?

And that heat had to do something such as warm up the air and stuff .. ya know... stuff... like what you feel when you are at a camp fire... melt marsh mellows and other stuff.

Come on scientists... how hot?

[OneWhiteEye]

OK...

That seems odd...

Odd that it's hard to do analytically? At first glance, I would've guessed impossible, and perhaps I'm right. The energy for fracture scales with the resulting surface area - simply the difference between a very rough surface and a very smooth surface after fracture could be a factor of two in area.

...but let say you drill a X diameter hole in material Y... z inches deep.. we can compute the volume of the material destroyed by the drilling... even I can do that... We can also meter the electricity used to run the drill.. measure the heat change in the motor itself and in the shavings and the region around the hole. That is an experiment I can conceive of in my mind and maybe could do in a lab environment.

In essence, that's what the people did in the study.

I know the metal shavings are damn hot! I don't see why concrete would be much different... but that would depend on the matrix which holds it together. Fibreglass gets hot too.

I think you're right, I think the heat was very significant. The problem is in trying to quantify it. I can also smoke a drill bit just spinning it in the hole it's already made. Virtually no mechanical work being done on the material, just pure friction. Making the heat energy simply the deficit between available energy and comminution energy is probably too naive. The Dr. G quote above would indicate 95% ends up as thermal, if that were the case. That seems too high (to me).

One would think that it's possible to come up with a range of heat released with some quickie math (the kind I can't do). It seems that if 100,000 tons of concrete is *dustified* to use their term...mechanically... you would have a hell of a lot of heat produced... No?

Can probaby put an upper bound on it, but not a lower bound.

Come on scientists... how hot?

I'll give it a whirl. It'll be a little while, and it probably won't be very good...

[SanderO]

Owlie,

That would be super... No rush... we've been at this for years and I am only beginning to grasp what seems like magic... ergo bombs dunnit.

I don't know that such a calculation will impress anyone... especially if they can't understand it. You have to use analogies with everyman... like metal shavings or hot sanding paper or wood... but of course with saw and milling dust and filings they are so small and give up their heat to the air we don't perceive sawdust as hot for example. I suspect even the shattering glass releases heat...

If there was oodles of heat it could possibly explain a lot of what appears to be mysteries and only what a bomb could do.

However, if the structures DID have knowable Achilles heels... as I think they did and we've kinda found them "after the fact".... though they could have been found before the fact... it wouldn't take all that much mischief to kick off the collapses and it would hidden by all the "natural" processes of the collapse.

The Miamus River bridge collapsed from failed single pin connection... the straw that broke the camel's back... from corrosion.. but it could have perhaps been blown out with a pretty small charge too...

I don't know that one could prove that the kick off was not mischief if we can demonstrate that those structures were ticking time bombs on very thin stiletto Achilles heels.

Eureka! A name for a line of ladies shoes... Achilles Heels

[OneWhiteEye]

I don't know that such a calculation will impress anyone... especially if they can't understand it.

I'm afraid that's true. The reasoning is sound, though. A barrage of calculations may not be worth much.

[OneWhiteEye]

I'm going to craft a letter to the people who did the thermal efficiency study linked above to try and extract every bit of useful information they're willing to give.

[SnowCrash]

Cool thread.

[Oystein]

SanderO is basically asking how much temperature of the debris would be increased by the collapse, through whatever mechanical processes.

An upper (and unrealistic) bound for the average temperature can easily be computed:


Let's start with an object of mass 1 kg that gets ejected from the roof of a twin tower and falls to the ground.

It's potential energy relative to the ground is m*g*h = 1 kg * 9.8 m/s² * 415 m = 4067 J.

Supposing all this energy is eventually turned into heat, and all the heat goes into the object, it's thermal energy will increase by these 4067 J. The associated temperature increase depends on the material's heat capacity, which is usually given in J/(mol*K) but could also be expressed in J/(kg*°C):

delta-T = Energy/(mass*heat capacity)

According to http://en.wikipedia.org/wiki/Heat_capacity
- the heat capacity of iron is 450 J/(kg*°C)
- the heat capacity of concrete is 880 J/(kg*°C)
- the heat capacity of aluminium is 897 J/(kg*°C)
- the heat capacity of gypsum is 1,090 J/(kg*°C)
- the heat capacity of wood is around 1,700 J/(kg*°C)

So the potential energy of 1 kg falling from 415 m would heat 1 kg of iron by (4067/450)°C = 9°C, 1 kg of concrete by 4.6°C and 1 kg of wood by 2.4°C.

Not a lot, eh?

Now of course the average height of fall of the building mass wasn't 415 m but less than half that, perhaps 40% or 166 m.

And of course some of the heat also goes into the ground that the rubble falls on, and lots goes into fracture and deformation. All in all, the average temperature of the building materials was probably raised by less then 1°C by the collapse itself. Of course it is entirely possible that bits and pieces, like surfaces, beam ends, etc. experienced very localised stresses and friction that raised their temperature more significantly, perhaps to the point of procucing sparks, but potential energy of the building height is insignificant when it comes to explaining the elevated temperartures of the pile. Chemical energy of combustible building materials surpassed the potential energy by several orders of magnitude.

[OneWhiteEye]

Good answer!