andrem@pyrman2.pyramid.com (Andre Molyneux) (02/09/91)
From: andrem@pyrman2.pyramid.com (Andre Molyneux) In response to: >>From: MEDELMA@CMS.CC.WAYNE.EDU (Michael Edelman) >Message-ID: <1991Feb8.012544.15685@cbnews.att.com> >Thos Cohen asks "how long does it take for 36m of concrete to cure?", >with regards to Iraqi shelters. The answer: No longer than it takes >1m to cure. I thought I'd relate some information I received on a tour of Hoover Dam about 5 years ago: During the tour, the guide asked how many people had heard that workers on the dam had been killed by being buried during the pouring of concrete. When several people raised their hands, he told us that such stories were hogwash since concrete won't cure correctly if it is poured more than 8 inches at a time. To emphasize this, he pointed out pictures showing the building of the dam. Sure enough, you could see concrete being poured into wooden-sided molds that couldn't have been more than 1 foot high. On a related note, I recently saw a BBC show on Greek and Roman architecture that mentioned the use of concrete in Roman projects. The host told how the Romans poured the concrete in layers, and how they had to pour each layer a little before the one before it had completely cured. In this way the many layers of concrete effectively became one piece. Anyone have experience with recent techniques for pouring large quantities of concrete? ------------------------------------------------------------------------------ Andre Molyneux - KA7WVV - andrem@pyrman2.pyramid.com PYRAMID TECHNOLOGY CORPORATION 1295 Charleston Road, Mountain View, CA 94043 "Insert your favorite corporate disclaimer here."
jgd@Dixie.Com (John G. DeArmond) (02/13/91)
From: jgd@Dixie.Com (John G. DeArmond) jln@elaine39.stanford.edu (Jared Nedzel) writes: >As for times, well, a 36m slab of concrete would certainly have to be placed >in lifts, with time between lifts (just how much time, I'm not sure). >It will take somewhere between several hours and a day or two for the >concrete to set, but it will take significantly longer for it to gain >strength. You get a lot of strength after a week, but you won't reach >design strength for a month or so. I can't say how long it would take >to pour 36m of concrete, except to say that it would be a good long >while (months). My first "real" job was as a heavy equipment operator at the construction site of the Sequoyah Nuclear Plant in Chattanooga, TN. More specifically, I ran the ammonia-cooled ice plant that was part of a field-erected concrete batch plant. I started my job a couple of weeks before the pour of the reactor building foundation. This was a slab about 200 ft in diameter and 35 ft thick. This slab was laid as a continuous pour. It took about 3 weeks of around the clock pouring to lay it. To put this in perspective, the batch plant was about 6 stories high, received its raw materials by river barge and mixed a truckful in a single batch. The ice plant alone had 200 hp motors running the ammonia compressors. In other words, we could make a LOT of concrete. It'd be hard for me to imagine a batch-plant this large being transported out in the desert away from grid power. I suppose it could be done. I think that the 3 week period for a pour this size is probably the minimum one could expect. John -- John De Armond, WD4OQC | "Purveyors of speed to the Trade" (tm) Rapid Deployment System, Inc. | Home of the Nidgets (tm) Marietta, Ga | {emory,uunet}!rsiatl!jgd |"Politically InCorrect.. And damn proud of it
pt@dciem (Paul Tomblin) (02/15/91)
From: cognos!geovision!pt@dciem (Paul Tomblin) andrem@pyrman2.pyramid.com (Andre Molyneux) writes: >In response to: >>>From: MEDELMA@CMS.CC.WAYNE.EDU (Michael Edelman) >>Message-ID: <1991Feb8.012544.15685@cbnews.att.com> >>Thos Cohen asks "how long does it take for 36m of concrete to cure?", >>with regards to Iraqi shelters. The answer: No longer than it takes >>1m to cure. [stuff deleted] >several people raised their hands, he told us that such stories were hogwash >since concrete won't cure correctly if it is poured more than 8 inches at a >time. To emphasize this, he pointed out pictures showing the building of >the dam. Sure enough, you could see concrete being poured into wooden-sided >molds that couldn't have been more than 1 foot high. Yes, it's still true. As a matter of fact, one of the most common uses of finite element analysis is to model the heat flow out of curing concrete in large structures such as dams. (Or as we called it in school, Damn Finite Elements) The major problem with pouring big blocks of concrete is that heat is generated by curing. Lots of it. If you pour a big block in one go, the thermal expansion is enough to crack it. -- Paul Tomblin, Department of Redundancy Department. ! My employer does The Romanian Orphans Support Group needs your help, ! not stand by my Ask me for details. ! opinions.... pt@geovision.gvc.com or {cognos,uunet}!geovision!pt ! Me neither.
thos@softway.sw.oz.au (Thomas Cohen) (02/21/91)
From: thos@softway.sw.oz.au (Thomas Cohen) In article <1991Feb18.054239.11447@cbnews.att.com> yarvin-norman@CS.YALE.EDU (Norman Yarvin) writes: > >A figure was mentioned of a German shell which penetrated 36m of Maginot Line >concrete. > >Does anybody know whether this rumor was true? > Ain't no rumour. Following taken without permission from (you guessed it) "The Illustrated Encyclopedia of Ammunition", by Ian Hogg. Spelling errors etc. are mine. Rochling Shell "Special type of anti-concrete shell developed by the Rochling Eisenund und Stahl-werke of Dusseldorf, Germany during WW2. Conventional anti concrete shells of the period were full calibre shells with blunt points; the Rochling designers reasoned that better penetration would be achieved by a shell of small calibre, but delivering a heavier blow by virtue of being much longer than normal and thus concentrating its weight into a smaller area of contact. They accordingly designed a long sub-calibre shell with a discarding sabot at the shoulder and a sabot at the rear which enclosed a set of four flexible fins. When fired, the shell left the muzzle and discarded the two sabots, allowing the fins to spring out and stabilize it. It was fired from a 21cm rifled gun, but the fins soon damped out the spin. The Rochling shell was not used against the Maginot line during the 1940 invasion of France, since it was not necessary. After the occupation of France and Belgium a number of trials were made against fortifications and one record of these tests reports of a shell which passed through 3m of earth [ sorry, in the original posting I said 5m ], 36m of concrete, a layer of broken stone, the roof of a subterranean chamber then into the floor beneath and 5m into the earth beneath the floor. This was a test of an inert shell; a live shell would have detonated in the subterranean chamber if correctly fused. Achievement of this kind of performance demanded high grade chrome- vanadium steel for the shell and precise manufacture. 8000 shells were made and stockpiled, but after that it was hardly used. A few were fired against the fortress of Brest-Litovsk during the invasion of Russia in 1941, but use of the Rochling shell was then forbidden by Hitler on the grounds that a specimen might fall into enemy hands and be copied for use against Germany. From then on the shells could only be used with his permission, and since this was rarely requested and even more rarely granted, the existence of the shell was gradually forgotten." -- thos cohen |Softway Pty Ltd "Stopping to pick up passengers would disrupt |ACSnet: thos@softway.oz the timetable" - Alderman Cholerton, on why|UUCP: ...!uunet!softway.oz!thos the council's buses didn't stop for passengers|Internet: thos@softway.oz.au