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Politics : Foreign Affairs Discussion Group -- Ignore unavailable to you. Want to Upgrade?

To: Doug R who wrote (203025)	9/16/2006 11:06:27 PM
From: Bilow	Read Replies (1) \| Respond to of 281500

Hi Doug R; Re: "George Pataki, on site, after collapse, describing how there was NO concrete at all in the rubble...that it was all pulverized." Pataki had no way of knowing that. The finer dust takes the longest to settle and ends up on the top. So when you look at it, before you dig into it, it might look like there's no concrete, but as you dig deeper you will find the big chunks of concrete. And any way, reasonable engineering design will put the heavyweight concrete on the bottom portions of buildings and the lightweight concrete on the top portions, so in a collapse like the WTC you will see the results of what happens to the lightweight concrete on the top of the pile. But the concrete was not all created equal and it could not all respond equal. Leach managed the debris flow while many law enforcement agencies analyzed every single speck of it two or three times. The work was an assembly-line operation with grappling derricks hefting twisted steel and huge chunks of concrete from barges onto trucks. The trucks carted the debris from the barges to sorting centers where it was sifted by size. hq.usace.army.mil Machinery bought by Taylor and installed at the landfill separates the rubble with screening equipment, divides the rubble based on size and distributes the metal pieces, concrete chunks and other items to a pair of conveyor belts. ... Personal items found amid the chunks of concrete and steel on the conveyor belts are placed in a plastic bucket. Besides combing out body parts, agents find badges, social security cards, watches, wallets and children's clothing from a store. About 10,000 pieces of personal belongings have been recovered so far. epa.gov The search has been methodical and exhaustive. The rubble is spread out and inspected twice at Ground Zero. Then it’s brought to Fresh Kills by barge and truck, where the clumps of tangled metal and concrete are broken down using heavy machinery and vibrating belts. npr.org According to Morse, the debris contains a wide variety of materials. "If you can imagine it, it's probably in there -- freon, fuel, and other substances are in the debris. The concrete in the floors and exteriors was lightweight; that was the dust you saw during the collapse." hq.usace.army.mil So how much energy does it take to pulverize lightweight concrete? Not much. Here's a reference: Lightweight Aggregate Lightweight aggregates are used to make lightweight concrete. Lightweight aggregates can be processed natural materials (for example expanded clay or expanded shale), processed by-products (for example foamed slag or sintered pulverized fuel ash) or unprocessed materials (for example pumice). logicsphere.com So it seems that the lightweight concrete that was used in the slabs of the WTC was quite weak and easy to pulverize, certainly not comparable to even a fraction of the strength of rock like your guy's calculations used. Instead of being filled with little stones, it's filled with weak stuff such as pumice (which is light enough to float on water and so weak you can easily grind two pieces up with your bare hands). But as my calculations showed, the majority of the concrete in the building was not in the floor slabs and so was likely to be normal weight concrete in the lower part of the building. It was this normal weight concrete that ended up carted off in huge blocks and chunks, and it would be the normal weight concrete that accounted for most of the concrete used in the building. And even among the lightweight concrete there was plenty that survived. For example: Smaller debris blown from WTC 1 and WTC 2. In particular, several small chunks of lightweight concrete, which appeared to be from WTC 2 floor slabs, were thrown through the north windows of the building. These debris items ranged in size from small fragments that caused bullet-size holes in the windows to large chunks with a maximum dimension of approximately 12 inches. Many of these chunks landed as far as 15 feet from the exterior building line and appeared to be traveling almost horizontally when they penetrated the building facade. thewebfairy.com Gradually we are learning more about concrete eh? -- Carl