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Post by JayUtah on May 12, 2006 14:17:04 GMT -4
The heat shield on the Apollo CM was a direct descent of ablative shields used on weapon re-entry modules. The combination of phenolic resin in a mechanical substrate was borrowed from military technology developed for nuclear warheads.
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Post by bazbear on Jul 21, 2006 20:58:18 GMT -4
There are dry powders that take an imprint perfectly well like cement and talcum powder. This has been always my lament about this claim; I've known things like baby powder would do this as long as I can remember. But of course, it seems to HBers that "real world" experiences are only valid if they counter the historical facts.
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Post by orumdude on Sept 9, 2006 9:47:07 GMT -4
Baby powder and cement contain moisture, that's why the take footprints.
"it seems to HBers that "real world" experiences are only valid if they counter the historical facts. "
Sure thing dude, you're cool with me.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Sept 9, 2006 10:59:37 GMT -4
... cement contain moisture, Powdered cement does not contain moisture, that it why it is powered. Hydrating cement is what causes it to harden.
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Post by orumdude on Sept 9, 2006 11:08:23 GMT -4
... cement contain moisture, Powdered cement does not contain moisture, that it why it is powered. Hydrating cement is what causes it to harden. Is that true dude, then why is these clever guys here selling a device that measures the moisture content of cement. You better tell them they're wasting their time and possibly comitting fraud. Silly dudes. www.mastrad.com/spear.htm
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Sept 9, 2006 12:23:48 GMT -4
Dry Portland cement may contain minute trace amounts of water, but water in any appreciable quantity will ruin it, which is why there is a device to test for this. For instance, unprotected cement can pick up humidity from the air, causing it to become lumpy and hard.
Your premise that moisture in the cement is the reason it can record deformations is completely ignorant. If the moisture content were high enough for this to be the case, the hydrated cement would crystallize.
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Post by orumdude on Sept 9, 2006 12:33:59 GMT -4
Dry Portland cement may contain minute trace amounts of water, but water in any appreciable quantity will ruin it, which is why there is a device to test for this. For instance, unprotected cement can pick up humidity from the air, causing it to become lumpy and hard. Your premise that moisture in the cement is the reason it can record deformations is completely ignorant. If the moisture content were high enough for this to be the case, the hydrated cement would harden. You speak as if you know something about this subject, are you a trained expert ?
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Post by hplasm on Sept 9, 2006 14:41:17 GMT -4
Dry Portland cement may contain minute trace amounts of water, but water in any appreciable quantity will ruin it, which is why there is a device to test for this. For instance, unprotected cement can pick up humidity from the air, causing it to become lumpy and hard. Your premise that moisture in the cement is the reason it can record deformations is completely ignorant. If the moisture content were high enough for this to be the case, the hydrated cement would harden. You speak as if you know something about this subject, are you a trained expert ? Now you've done it... *sound of knives being sharpened*
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Sept 9, 2006 14:43:17 GMT -4
You speak as if you know something about this subject, are you a trained expert ? I have a civil engineering degree and work for a general construction contractor. Although I'm not an expert on cement specifically, I have knowledge of the subject.
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Post by orumdude on Sept 9, 2006 14:52:01 GMT -4
You speak as if you know something about this subject, are you a trained expert ? I have a civil engineering degree and work for a general construction contractor. Although I'm not an expect on cement specifically, I have knowledge of the subject. I think if you were being honest you would say you had insufficient knowledge to make a judgement of the moisture content of cement as seen by the poster who mentioned it. Common sense says that cement lying on the ground will have picked up moisture from the atmosphere and the earth.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Sept 9, 2006 15:43:11 GMT -4
Common sense says that cement lying on the ground will have picked up moisture from the atmosphere and the earth. And that would render the cement clumpy and unusable, which is why cement isn't left laying around on the ground. Cement has to be stored in a dry place so that it doesn't absorb the moisture that will ruin it. Adding water to Portland cement rearranges the structure of the active compounds causing them to crystallize. If this occurs in a concrete mixture, the crystallized cement bonds the aggregate particles together forming a hard and durable concrete. If the cement is exposed to water before it is used in a concrete mix, in storage for example, it crystallizes and it no longer useful as concrete binder. It must therefore be kept absolutely dry or it's worthless. Newly made Portland cement is virtually devoid of moisture. It is manufacturer by heating the raw materials to nearly 3,000 o F in a kiln, which drives off all the water.
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Post by orumdude on Sept 9, 2006 17:34:43 GMT -4
"Newly made Portland cement is virtually devoid of moisture."
That isn't what he was talking about, you can't put footprintson cement unless it is lying on the ground.
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Post by nomuse on Sept 9, 2006 17:53:06 GMT -4
'Dude, I'd like to see you stick around. Please back away from the brink here. Unless you are angling for a suspension. In this thread you've been basically well-behaved, and worth talking with. I don't know what you are doing in some of the more political threads but that warning bar you are getting scares me.
But back to the subject. Portland cement isn't a magical wick. If it instantly absorbed all available moisture in its environment it would be useless as a building material (it make make an interesting weapon for a super-villian, tho!)
Be that as it may. Portland cement in a dry vacuum such as exists on the Moon, would exhibit similar characteristics to lunar dust. Some of this behavior (such as the ability to take crisp footprints) can be approximated under ordinary room conditions.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Sept 9, 2006 19:33:17 GMT -4
"Newly made Portland cement is virtually devoid of moisture." That isn't what he was talking about, you can't put footprintson cement unless it is lying on the ground. You can make indentations in Portland cement while it is still in the bag and bone-dry. You don't have to spread it on the ground and walk on it to demonstrate conclusively that a deforming object will leave lasting indentations.
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MarkS
Earth
Why is it so?
Posts: 101
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Post by MarkS on Sept 10, 2006 8:09:29 GMT -4
So imagine a "South Pole Hoax" believer in 1950 saying "If we went to the pole, why can't we go to the pole? It's impossible, that's why. Proof that Amundsen and Scott faked it all". Well, they don't need to be from back in the Fifties. There are no 'poles,' per se; turns out the Earth is hollow and the poles are the access points. See freespace.virgin.net/seant.ellis/holespoles.htm If one does a Google search of 'polar openings' one receives a distressingly high number of hits.
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