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Natural Science Forum / Physics / General Physics / September 2007Poor design led to I-35W bridge collapse?
This image shows the ground supports of the bridge before the collapse: http://www.wmur.com/2007/0802/13805989_240X180.jpg taken from: Nation's Bridges Face Immediate Inspection. Fifth Victim Found; President Bush To Visit Minneapolis UPDATED: 9:20 am EDT August 3, 2007 http://www.wmur.com/news/13801620/detail.html A video of the collapse is also available on this page. Note the ground supports are slender concrete columns. Note also the steel arch only extends to the top of the support. It does not extend down into the ground. In contrast note the arches of the 10th Avenue bridge next to the collapsed bridge extend into the ground: 10th Avenue Bridge. http://en.wikipedia.org/wiki/10th_Avenue_Bridge The strength of an arch extends from its curvature. Note that an arch of the I-35W bridge not extending into the ground means the arch is shorter which necessarily makes the arch straighter, and therefore weaker. The 10th Avenue Bridge also has supports in the middle of the river while the I-35W bridge did not. Compared to the supports of the 10th Avenue Bridge, the ground supports of the I-35W bridge can only be described as flimsy. This is a bridge that carries the most traffic in the state of Minnesota. Moreover the 10th Avenue bridge only has to carry 2 lanes, while the I-35W carried 8. A professor at Northwestern argues the failure was likely due to the joints connecting the bridge to the concrete supports: Investigators in bridge collapse focus on chilling video. By Jon Hilkevitch | Tribune transportation reporter 9:41 PM CDT, August 2, 2007 "The bridge must have been near a state of collapse for some time, and the construction might have contributed to its failure," said Zdenek Bazant, a professor of civil and environmental engineering at Northwestern University. Bazant said he suspects there may have been a hairline crack or fatigue in the steel joints near bridge supports, leading to the buckling" http://www.chicagotribune.com/services/newspaper/premium/printedition/Friday/chi -070802bridge,0,3911616.story?page=2 This page on the I-35W describes it as a truss bridge: I-35W Mississippi River bridge. http://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge These are among the cheapest and flimsiest of bridges. They lack the redundancy of many other types of bridges: Investigators in bridge collapse focus on chilling video. By Jon Hilkevitch | Tribune transportation reporter 9:41 PM CDT, August 2, 2007 "Other engineering experts said that the 1960s-design of steel-arched bridges did not contain structural redundancies, meaning that if one component fails, the whole structure is in jeopardy because the weight does not shift to other points on the bridge. "We know that we would not build a bridge like this today,'' said Kent Harries, an assistant engineering professor at the University of Pittsburgh." http://www.chicagotribune.com/services/newspaper/premium/printedition/Friday/chi -070802bridge,0,3911616.story?page=2 Bob Clark Dear Robert Clark: > This image shows the ground supports of the bridge > before the collapse: The bridge was inspected and noted to have accumulated flaws: 1) corrosion in / near bearing surfaces (a maintenance item), and 2) fatigue cracks (indicating loading or aging in excess of design). Maintenance on *these things* were not underway. They decided to inspect it more often, to see if maybe inspection would fix them. They can afford inspectors, but they cannot / would not afford the repairs. And there are 17,000 more bridges with similar diagnoses. The purpose of government is to do for the people what they cannot do for themselves. "Lack of planning" they can do for themselves. It takes government to "cut taxes at the expense of basic services". Robert, I don't think it was the engineering. I'd bet the engineer that designed the bridge did not design it for an infinite, (effectively) unmaintained lifetime. And I'd also guess that there are more lanes of traffic painted across that stretch of concrete than the engineer was told to design for so many years ago. I'd say (from my armchair) the root cause was routinely exceeding the design loading and not performing necessary maintenance. David A. Smith > This image shows the ground supports of the bridge before the > collapse: [quoted text clipped - 65 lines] > > Bob Clark "The purpose of government is to do for the people what they cannot do for themselves. "Lack of planning" they can do for themselves. It takes government to "cut taxes at the expense of basic services". This is not true, I have yet to see the government bring me a beer while I am watching the Science Channel. The purpose of the government is to provide the fundamentals and infrastructure for the general walfare of society. There are some highways and bridges built entirely from private funds and users are charged a fee to driven on them. But generally, roads and bridges are the domain of government. The MN State government obviously failed to provide adequate maintenance for their bridges, electing to provide "More of something else" to their electorate, to "buy" a few more votes for specific politicians, at the expense of the infrastructure. "I'd say (from my armchair) the root cause was routinely exceeding the design loading and not performing necessary maintenance." I absolutely agree with this conclusion, but it will take a few months investigation to determine exactly what failed, initially, but when the big pircure is modeled, the above will most likely sum it up. > This image shows the ground supports of the bridge before the > collapse: [quoted text clipped - 60 lines] > > Bob Clark I am in agreement. The flimsy support is quite vulnerable to mechanical damage and corrosion. The consequence of damage/loss of this support is a design disaster... down-grading the entire bridge from a locally fixed shallow arch to a stiffened plate with edge- truss stiffeners, a massive loss of bend/twist rigidity of the arch. It is like removing the keystone not exactly at the center, but like removing some stones at quarter points.An arch of increasing reinforcement cross-sections designed all the way to the base/ground was needed and that should not have been compromised when once began at the mid-span.It would have responded better to unanticipated off- design loads like corrosion weaknesses or flutter of a ribbon bridge assisted by dysfunctional joints. The tell-tale picture shows fracture roughly at the zones of sudden loss of bend/twist stiffness across span. Narasimham Dear Narasimham: ... > I am in agreement. The flimsy support is quite vulnerable > to mechanical damage and corrosion. The consequence [quoted text clipped - 3 lines] > stiffeners, a massive loss of bend/twist rigidity of the > arch. Was it not designed for the design loads "40 years" ago, with the expectation of reasonable maintenance? > It is like removing the keystone not exactly at the > center, but like removing some stones at quarter points. [quoted text clipped - 5 lines] > weaknesses or flutter of a ribbon bridge assisted by > dysfunctional joints. The expected mode of failure was triggered by "fatigue" and "corrosion". Both of which require maintenance. In 2005, had they responded by reducing the number of lanes across this bridge, until funds could be had to do actual repairs, we would or would not be having this discussion? > The tell-tale picture shows fracture roughly at the > zones of sudden loss of bend/twist stiffness across > span. Your area of expertise is... ? David A. Smith > Your area of expertise is... ? I'm interested in reading what your area of expertise is. Dear Irving Layton: >> Your area of expertise is... ? > > I'm interested in reading what your area of expertise is. Licensed professional mechanical engineer in the State of Arridzona. Got my degree in machine design (graduated with honors from Arizona State University). And I have seen "politicians" find more room on the top of bridges for more than 50 years. And "inspect until the problem goes away" for almost as many years. Are you satisfied, or do you care to snipe some more? The person I was responding to seemed to have some failure analysis capability. I enjoy talking to someone who knows what they are talking about. David A. Smith On Aug 5, 10:47 am, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> wrote: >> I'm interested in reading what your area of expertise is. > [quoted text clipped - 7 lines] > > Are you satisfied, or do you care to snipe some more? Someone simply asking "I'm interested in reading what your area of expertise is" should not be considered a sniper. That is a very legitimate question. On Aug 4, 3:01 pm, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> wrote: ... > The expected mode of failure was triggered by "fatigue" and > "corrosion". Both of which require maintenance. > > In 2005, had they responded by reducing the number of lanes > across this bridge, until funds could be had to do actual > repairs, we would or would not be having this discussion? ... An article in todays Minneapolis Star/Tribune newspaper has some disconcerting information about previous inspection reports. http://www.startribune.com/10204/story/1350090.html State bridge inspectors warned for nearly a decade before its collapse that the Interstate 35W bridge had "severe" and "extensive" corrosion of its beams and trusses, "widespread cracking" in spans and missing or broken bolts. Not only was the superstructure in poor condition, but certain components were "beyond tolerable limits," and one of the bridge's piers had "tilted to the north," they reported. By 2000, the inspectors wrote that "eventual replacement of the entire structure would be preferable" to redecking the bridge. They added: "If bridge replacement is significantly delayed, the bridge should be re-decked." That recommendation was repeated in every report afterward, but it never happened. Since the collapse, public attention has focused on consultant reports in 2006 and 2007 that expressed serious reservations about the bridge. But a Star Tribune review of older reports by state inspectors shows that their concerns had been growing since the mid-'90s. ... However, in every report since 2000, inspectors urged the state to replace bolts in a specific area of the bridge, a job listed each year under "Immediate Maintenance Recommendations." .... "The fatigue cracks in the approach spans that occurred in the late 1990s were addressed by repairs and retrofitting of connections," MnDOT spokesman Kevin Gutknecht said in a written statement. He added that early replacement of the bridge was not considered in part because "no fatigue cracks had occurred in the main truss spans." ... In 1996, reports took on an urgent tone In many cases the reports simply lay out a long list of problems found rather than rating their severity, but in 1996 the inspectors began to take an urgent tone. Noting that a pier supporting steel spans had tilted to the north, the inspectors warned then, "As this will not be repaired in the near future, this area should be closely inspected!" In 1998, inspectors wrote that "numerous fatigue cracks were found" in the approach spans on the north and south sides of the bridge, which was then three decades old. The report said the cracks were drilled out and the fractured beams reinforced with bolted plates. ... The 1999 report said those cracks were among "areas of major concern," adding that "due to the widespread cracking these areas will now be inspected on six-month intervals." Later reports recommended only annual inspections. Gutknecht said no further cracking was reported after November 2000, so the monitoring cycle was increased. ... The university's research concluded in 2001 that "fatigue cracking of the deck truss is not likely",...."As a result, MnDOT does not need to prematurely replace this bridge because of fatigue cracking, avoiding the high cost associated with such a large project." ... But MnDOT inspectors continued to express concern about fatigue cracking after the university report and the department asked the engineering design consultant URS to review the bridge's condition. URS in 2006 expressed concerns that a serious fatigue crack might go undetected because of the difficulty in inspecting parts of the bridge that were difficult to reach. URS recommended steel plating as a fix. But MnDOT engineers asked URS to come up with other options and the department ultimately chose an alternative that called for increased inspections and repairing any problems found. URS called that option the "most cost efficient," but warned that "the critical issue of this approach is to ensure" that inspectors don't miss any measurable flaws. Chief bridge engineer Dan Dorgan said previously that MnDOT chose the inspection option because it worried that drilling to add plates might weaken the bridge. On Aug 5, 1:01 am, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> wrote: > Dear Narasimham: > [quoted text clipped - 35 lines] > > David A. Smith Structural / Mechanical design engineering for Space launched Composite Structures,about 30 years. Regards, Narasimham Dear Narasimham: > On Aug 5, 1:01 am, "N:dlzcD:aol T:com \(dlzc\)" <d...@aol.com> wrote: ... > > > The tell-tale picture shows fracture roughly at the > > > zones of sudden loss of bend/twist stiffness across [quoted text clipped - 4 lines] > Structural / Mechanical design engineering for Space > launched Composite Structures,about 30 years. Space Shuttle, weapons, or "domestic" structures? Anything that does reuse, multiple cycles (like the external tank of the SS was supposed to)? I was flabbergasted by this: http://otrc.tamu.edu/Pages/currentwheat.html ... never really thought about carbon composites "corroding". David A. Smith > Dear Narasimham: > [quoted text clipped - 8 lines] > > Structural / Mechanical design engineering for Space > > launched Composite Structures,about 30 years. ---- > I was flabbergasted by this:http://otrc.tamu.edu/Pages/currentwheat.html > ... never really thought about carbon composites "corroding". There is water under pressure.It is in contact with carbon through micro-cracks in the cured resin.(There is a large difference of CTE between the epoxy resin and carbon. When thermal curing stresses are removed, it results in micro cracks throughout). Even a small degree of galvanic corrosion may be there. Even TREK bicycles were affected without a thin fiberglass isolating sleeve between carbon and aluminum tubes.There may be metallic elements in the TLPs (tension leg platforms)surroundings.In offshore application however small,corrosion cannot be ignored as the safety of an entire oil drilling rig will be in jeopardy.. Regards, Narasimham > David A. Smith > This image shows the ground supports of the bridge before the > collapse: [quoted text clipped - 60 lines] > > Bob Clark --------------------- i dont ahve much information about thespecific case yet we know generally that steel bridges has a severe problem of corrosion OTHOH concrete bridges ar emuch better from tha tpoint of vew ie much less maintanance problems that is th emain reason that in our counrty we refrain as much as possible from steel bridges of corrosable steel (there are kinds of much less corrosion valnearble steels th e'fatigue of steel is as well a factor yet we ahve to remember that that bridge was holding on i think more than 40 years !! moreoever the sayndards of desighn take in acount fatigue of material and itis taken in acount in a bigger safely factor (salmmer stresses ) so my guess would be tha tit was more a problem of bad maintanance!! yet of course i cant judge from tousands of miles away wihtout al lthe needed data and facts anyway if it ia systemtic problem it is obvious that there is an urgaent need to avoid further disasters .. just immagine what could happen if that bridge was not falling to water but on a running train..... ATB Y.Porat ---------------- > i dont ahve much information about thespecific case > yet we know generally [quoted text clipped - 9 lines] > (there are kinds of much less > corrosion valnearble steels Concrete is not stone, you have problem with carbonation and resistance against a lot of chemicals. A concrete bridge will not last for ever unless you replace some of the concrete now an then. > th e'fatigue of steel is as well a factor > yet we ahve to remember that that bridge [quoted text clipped - 5 lines] > so my guess would be > tha tit was more a problem of bad maintanance!! Fatigue problems are design problems. If you don't call it maintenance to replace details that have shown to have a shorter lifespan than that of the rest of bridge. 40 years is not good for something supposed to last at least 100 years. But things like this have happened before, and probably will in the future also. http://www.bernd-nebel.de/bruecken/4_desaster/birs/birs.html Out of that accident came Tetmajers formula for inelastic buckling of slender columns.  SignatureMvh Anders Lagerås On Aug 5, 6:23 pm, Anders Lager?s <anders.lage...@gmail.com> wrote: > > i dont ahve much information about thespecific case > > yet we know generally [quoted text clipped - 13 lines] > against a lot of chemicals. A concrete bridge will not last for ever > unless you replace some of the concrete now an then. -------------- i forgot to tell you aht i am a bridge engineer with more than 40 years experiance... concrete is saied to last more than 15 years youare right that in some cases it has problems mainly if not properly desighned ie not enough cover of reinforvement stell or in sea while it demads special concret that is chlorine resistance and there are such . another problem is salt that is spread fo rdifrosting ice if can be as wel ahndles by soecial coating of the comcrete . yes the satndard of bridges deoand 100 - 150 years of use yeti guess in parctice i tcan last much longer. ---- ----- > > th e'fatigue of steel is as well a factor > > yet we ahve to remember that that bridge [quoted text clipped - 7 lines] > > Fatigue problems are design problems. ydt we dont know in that case if it was designed properly to acount for afatigue ithink that 40 yeaers ago th epeobemwas known btw th e fatigue businnes was brought to civil engineering from thr auronautics parctice .... it was know more than 40 years ago ---------- > If you don't call it maintenance to replace details that > have shown to have a shorter lifespan than that of the rest of bridge. if you are in a position of repalceing parts yo u are already in trouble (:-) a good desighn should amke you forget about repairings of concrete parts ---------- > 40 years is not good for something supposed to last > at least 100 years. yes i know it ---------- > But things like this have happened before, and probably will in the > future also.http://www.bernd- unfortuantely !! the goal should be-- to minimise it !! ATB Y.Porat ----------------- nebel.de/bruecken/4_desaster/birs/birs.html > Out of that accident came Tetmajers formula for inelastic buckling of > slender columns. > > -- > Mvh Anders Lager?s Dear Anders Lagerås: These charaters in your name are going to be butchered upon posting. My apologies in advance. On Sun, 05 Aug 2007 02:12:48 -0700 "Y.Porat" <y.y.porat@gmail.com> wrote: >> i dont ahve much information about thespecific case >> yet we know generally [quoted text clipped - 9 lines] >> (there are kinds of much less >> corrosion valnearble steels > Concrete is not stone, you have problem with > carbonation and resistance against a lot of > chemicals. A concrete bridge will not last for > ever unless you replace some of the concrete > now an then. Absolutely true. There are only two materials (as far as I know) that have an infinite fatigue life: iron loaded to less than 80% of hot rolled steel yield strength, and carbon epoxy composites (I don't recall the load limit, 40% of yield perhaps). Concrete will fail eventually. >> th e'fatigue of steel is as well a factor >> yet we ahve to remember that that bridge >> was holding on i think more than 40 years !! That is long for a food or software designer. But that is usually less-than-minimum life for a "permanent" bridge. >> moreoever the sayndards of desighn >> take in acount fatigue of material >> and itis taken in acount in a bigger >> safely factor (salmmer stresses ) >> so my guess would be >> tha tit was more a problem of bad maintanance!! > Fatigue problems are design problems. A fatigue problem *may* be a design problem. Catastrophic failure due to failure of a "single joint" is a design problem. Any structure that does not very conservatively load steel, and have no other materials in its construction, will have fatigue. And hence requires periodic maintenance, not just periodic inspection. > If you don't call it maintenance to replace details > that have shown to have a shorter lifespan than that > of the rest of bridge. Like the politicians-in-training that schedule, and actual politicians that fund, maintenance? It would not take much to cut the number of lanes that can be used during any hours, once a finding of "structurally deficient" has been made. > 40 years is not good for something supposed to last > at least 100 years. Do you have the design specifications for this particular bridge? * Was this a permanent routing for I-35W, * was this a temporary bridge that simply had its term-of-service extended, * was it designed for the traffic that it was getting 40 years after being put in service, * is it a design standard in Minnesota to make all bridges good for 100 years without maintenance? Politicians also fund least-cost design, and send work to those that meet their cost limits. Which would be shame on the engineering firm also, should that be the case here. > But things like this have happened before, and > probably will in the future also. http://www.bernd-nebel.de/bruecken/4_desaster/birs/birs.html > Out of that accident came Tetmajers formula for > inelastic buckling of slender columns. Or this one, due to contractor shortcuts: http://www.enm.bris.ac.uk/anm/tacoma/tacoma.html ... the engineer found that the contractor had used solid I-beams, rather than I-beams with holes cut in the web to reduce stiffness. He showed that to any that would listen, then committed suicide. Really, they could have cast iron in a monolithic structure down to bedrock. Why not argue that it is a design flaw that they did not do this? Civil engineering design, just like anything else, has cost limitations. And it is standard practice to *perform* maintenance on bridges... every municipality on the East Coast of the US with a bridge has a pretty significant annual maintenance budget. David A. Smith On Sun, 5 Aug 2007 09:14:24 -0700, "N:dlzc D:aol T:com \(dlzc\)" <dlzc@aol.com> wrote: >Do you have the design specifications for this particular bridge? >* was it designed for the traffic that it was getting 40 years >after being put in service? ... >David A. Smith Which reminds me: the first iron bridge there ever was, closed to traffic years ago. This bridge at Ironbridge, Bridgenorth developed multiple cracks in the cast ironwork, when traffic multiplied in weight and volume far beyond the Coalbrookdale ironmaster's expectations. Imagine that: After only two hundred years! Brian Whatcott Altus OK : On Sun, 5 Aug 2007 09:14:24 -0700, "N:dlzc D:aol T:com \(dlzc\)" : <dlzc@aol.com> wrote: [quoted text clipped - 13 lines] : : Brian Whatcott Altus OK You could have thrown in a picture :-) http://www.wku.edu/Geo/studyabroad/Britain04/ironbridge.jpg http://www.virtual-shropshire.co.uk/commenu/ironbridge.jpg > : >Do you have the design specifications for this particular bridge? > : [quoted text clipped - 14 lines] > http://www.wku.edu/Geo/studyabroad/Britain04/ironbridge.jpg > http://www.virtual-shropshire.co.uk/commenu/ironbridge.jpg Notably, the bridge has a high, curved arch, which extends all the way to the ground. Bob Clark : > : >Do you have the design specifications for this particular bridge? : > : [quoted text clipped - 19 lines] : : Bob Clark Imagine that... all the way down to the ground, huh? Amazing. I had a girlfriend with legs so long they went all the way up to her arse. So that's where McDonald's got the idea for their sign from... http://www.visitingdc.com/images/st-louis-arch-address.jpg >: Which reminds me: the first iron bridge there ever was, closed to >: traffic years ago. This bridge at Ironbridge, Bridgenorth developed [quoted text clipped - 3 lines] > http://www.wku.edu/Geo/studyabroad/Britain04/ironbridge.jpg > http://www.virtual-shropshire.co.uk/commenu/ironbridge.jpg Good thought! Brian W > On Sun, 5 Aug 2007 09:14:24 -0700, "N:dlzc D:aol T:com \(dlzc\)" > [quoted text clipped - 12 lines] > > Brian Whatcott Altus OK --------------- let me tell you again: th efart it was dolding on 40 years menas that the desighn was reasonable from load calculations aspect may be they ddint took in acount the right measures againt corrosion th eothers factor that i stoo pften occures is bad mainenence aginst corrosion and the best thing to do is building more concrete bridges (th e steel companies want like to hear it .......) Y.Porat ------------------------- ... > --------------- > let me tell you again: [quoted text clipped - 9 lines] > build more concrete bridges > (the steel companies won't like to hear it .......) Concrete bridges use steel rebar for strength at low mass. Although the concrete does provide some chemical buffering, it does not make the interior steel less prone to corrosion. Concrete is prone to brittle failure, is more difficult to non-invasively inspect, and is more difficult to repair. There is no substitute for maintenance. A monolithic structure (like a concrete span) can provide an excuse for not looking. David A. Smith > ... > [quoted text clipped - 22 lines] > > David A. Smith ----------- you are wrong about valnerability of reinforced concrete with steel the is a wonderful 'symbioisis' between concrete and steel for some aspects: 1 the termalexpansion of steel and concrete is nealt identical (which is a huge advantage and i would say luck as well 2 the concrete gives a wonderful protection tothe steel against corrosion (not only insulation protection but electrical curent protection-- sort of galvanizatin 3 it is right that if the buildes do not folow thwe standards of enough concrete cover on the steel it wilolblow up witht time 4 for corrosive envirinments like neer the sea or in cases of salt spread during freeze time there must be special concret with a deep enough cover to it (more thann 2 inch cover ) there is anothier thing to do against 'concrete corrotion' it is to cover it by pastic insulations or paintingands once you do it we call it 'built and forget about ' there is a need only tofiolow the neoprene bearings that has to be changes as now each about 30 years if tghere ar other bearinds it has to be done by noncorrosive steel (and there is such though much more expensive ) ATB Y.Porat ---------------------- ATB Y.Porat Dear Y.Porat: > > ... > [quoted text clipped - 27 lines] > you are wrong about valnerability of reinforced > concrete with steel No, I am not. I have tried installing equipment on a floor that had its rebar erode away (and the ground subside as well), and had a 6 foot drop over 200 feet. > the is a wonderful 'symbioisis' between > concrete and steel [quoted text clipped - 10 lines] > (not only insulation protection but > electrical curent protection-- sort of galvanizatin It passivates the surface. The rebar does still corrode to the point of failure. I have experience with this. > 3 > it is right that if the buildes do not folow thwe > standards of enough concrete cover on the steel > it wilolblow up witht time So maintenance is required. > 4 > for corrosive envirinments like neer the sea [quoted text clipped - 5 lines] > or paintingands once you do it we call it > 'built and forget about ' So maintenace is required, since the coatings erode over time. > there is a need only tofiolow the neoprene > bearings that has to be changes as now > each about 30 years > if tghere ar other bearinds it has to be done by > noncorrosive steel (and there is such > though much more expensive ) David A. Smith > Dear Y.Porat: > [quoted text clipped - 51 lines] > It passivates the surface. The rebar does still corrode to the point > of failure. I have experience with this. There are applications in which the rebar has a very good surface coating of epoxy in order to reduce/delay/eliminate (as much as possible) loss of strength to corrosion. Microfracturing of the concrete allows penetration by salt water on highways in US states where salt is used for ice and snow control. snip Dear nonsense: >> Dear Y.Porat: ... >>>2 >>>the concrete gives a wonderful protection [quoted text clipped - 10 lines] > reduce/delay/eliminate (as much as possible) > loss of strength to corrosion. Won't work on pre-stressed (like bridges) steel installations. Also won't work on more complex rebar structures that require welding, or torch cutting (like bridges). > Microfracturing of the concrete allows penetration > by salt water on highways in US states where > salt is used for ice and snow control. Like Minnesota on this particular which had persistent problems with "black ice". And they used lots of salt before they switched to runway deicer. And now the news comes out that heavy deposits of pidgeon poop were noted on the steel structure from the late 80's. Maybe they inspected that away too? By the way, pidgeon poop is especially hard on concrete. There are no maintenance-free structures. I understand that many do not agree that concrete makes inspection impossible, but I don't believe for a minute it makes maintenance unnecessary. David A. Smith > Dear nonsense: > [quoted text clipped - 18 lines] > > Won't work on pre-stressed (like bridges) steel installations. Usually done with cables, not rebar. > Also won't work on more complex rebar structures that require > welding, or torch cutting (like bridges). You probably ought to tell that to the people actually building the stuff. They clean the intersection, weld it, then paint it with epoxy paint. >>Microfracturing of the concrete allows penetration >>by salt water on highways in US states where >>salt is used for ice and snow control. > Like Minnesota on this particular which had persistent problems > with "black ice". And they used lots of salt before they > switched to runway deicer. Lots of north country continues to use salt. > And now the news comes out that heavy deposits of pidgeon poop > were noted on the steel structure from the late 80's. Maybe they > inspected that away too? By the way, pidgeon poop is especially > hard on concrete. Not real good for iron either. > There are no maintenance-free structures. I understand that many > do not agree that concrete makes inspection impossible, but I > don't believe for a minute it makes maintenance unnecessary. Radar is now in common use. It tells us something about the reinforcement as well as locating a core drill for sample retrieval without destroying reinforcement or pre stressing elements. Core drilling destructive test specimens out of roadways (bridges and otherwise) tells us about the quality of the concrete. >> Dear nonsense: >> [quoted text clipped - 55 lines] >specimens out of roadways (bridges and otherwise) tells >us about the quality of the concrete. But that would cost pots of money. I don't think that's part of what we've been calling "inspection". One of last week's reports of what is wrong with the Big Dig is that the concrete used to "waterproof" tunnels was watered down. I haven't looked up the chemistry of concrete yet, but too much water doesn't allow the concrete to harden...does it? /BAH >>>Dear nonsense: >>> [quoted text clipped - 57 lines] > > But that would cost pots of money. Naw. Ordinary concrete cutting contractors can afford the equipment which requires minimal training to use. Core samples are routinely taken from roads soon after construction to measure that the quality of the materials is up to spec, and as the road ages, to determine the extent of deterioration so that rebuild date can be better homes in on. > I don't think that's part > of what we've been calling "inspection". Cores are, radar is beginning to be. > One of last week's > reports of what is wrong with the Big Dig is that the concrete > used to "waterproof" tunnels was watered down. I haven't looked > up the chemistry of concrete yet, but too much water doesn't allow > the concrete to harden...does it? I'm fairly certain they're addressing the Massachusetts Irish faction who thinks anything "watered down" is a bad thing. Taking the sorts of artistic liberties reports of that sort often do, the watering down of concrete was probably done by using some other filler material which robbed the concrete of its strength. OTOH while excess water in concrete tends to make it cure more quickly and allows easier pouring and troweling, it does tend to rob the concrete of some of its potential strength (potential as in how strong could that blend of sand, gravel, and Portland cement become if properly used.) For me there's a clarity issue with the report you're citing. But then, just how would you explain this to the Massachusetts Irish in as few words as possible? "They sanded down the concrete?" While probably true, that description is even worse. Maybe by reducing the amount of Portland cement, "they stretched the concrete"? But the "watering down" is precisely why the government always takes core samples to testing whenever a new road is built. Even so it did take them a while to catch Palumbo in Chicago, who ground car interiors such as seats, door panels, and headliners into paving materials. Given Chicago's graft machine the contractor probably told the sample taker where to take the core samples and got by till some pavement deteriorated unexpectedly, revealing its contents prematurely. I think the extent of their punishment was to be banned from bidding any public projects for 20 years. They went from the largest regional excavator and road builder to zero overnight. >>>>Dear nonsense: >>>> [quoted text clipped - 65 lines] >to determine the extent of deterioration so that >rebuild date can be better homes in on. Where are these holes made? On the top or from the bottom? Do they fill them in after taking the sample? >> I don't think that's part >> of what we've been calling "inspection". > >Cores are, radar is beginning to be. I always thought that, the higher the tech, the more it costs. Does the radar device make a picture like an MRI does? >> One of last week's >> reports of what is wrong with the Big Dig is that the concrete [quoted text clipped - 8 lines] >probably done by using some other filler material which >robbed the concrete of its strength. Oh, not water but other stuff. damned news. This particular concrete was supposed to waterproof the tunnels. And the word slurry is a common noun used in the news reports. I don't know what that is either. >OTOH while excess water in concrete tends to make it >cure more quickly and allows easier pouring and >troweling, it does tend to rob the concrete of some >of its potential strength (potential as in how strong >could that blend of sand, gravel, and Portland cement >become if properly used.) I must be misremembering something my Dad said. I thought he'ld told me that too much water does not let it cure to hardness. It eventually falls apart. >For me there's a clarity issue with the report >you're citing. That's true about all the news these days. > But then, just how would you explain >this to the Massachusetts Irish in as few words as >possible? Liberals, honey. City slickers who believe that fairy tales are true ;-). >"They sanded down the concrete?" While >probably true, that description is even worse. Maybe [quoted text clipped - 4 lines] >government always takes core samples to testing >whenever a new road is built. That's why I keep wondering why the state chemist wasn't doing his/her job. I would have assumed that samples of the cement were taken before pouring. >Even so it did >take them a while to catch Palumbo in Chicago, [quoted text clipped - 5 lines] >deteriorated unexpectedly, revealing its >contents prematurely. Any bodies? ;-) I just read a bio about Daley, the father. I knew Chicago was bad but not that bad. >I think the extent of their punishment was to >be banned from bidding any public projects for >20 years. They went from the largest regional >excavator and road builder to zero overnight. Poor baby, can't bid. There are ways around that. I would have given him the task of fixing his mess-- one square foot at a time. /BAH >>>>>There are no maintenance-free structures. I understand that many >>>>>do not agree that concrete makes inspection impossible, but I [quoted text clipped - 19 lines] > Where are these holes made? On the top or from the bottom? > Do they fill them in after taking the sample? Top down. Yes, they are filled in. >>>I don't think that's part >>>of what we've been calling "inspection". >>Cores are, radar is beginning to be. > I always thought that, the higher the tech, the more it costs. > Does the radar device make a picture like an MRI does? I'm sure that someone scratching deeply can find one that doesn't store images but most do. Perhaps not quite like an MRI though. >>>One of last week's >>>reports of what is wrong with the Big Dig is that the concrete >>>used to "waterproof" tunnels was watered down. I haven't looked >>>up the chemistry of concrete yet, but too much water doesn't allow >>>the concrete to harden...does it? >>I'm fairly certain they're addressing the Massachusetts >>Irish faction who thinks anything "watered down" is a >>bad thing. Taking the sorts of artistic liberties reports >>of that sort often do, the watering down of concrete was >>probably done by using some other filler material which >>robbed the concrete of its strength. > Oh, not water but other stuff. damned news. This particular > concrete was supposed to waterproof the tunnels. And the word > slurry is a common noun used in the news reports. I don't know > what that is either. >>OTOH while excess water in concrete tends to make it >>cure more quickly and allows easier pouring and >>troweling, it does tend to rob the concrete of some >>of its potential strength (potential as in how strong >>could that blend of sand, gravel, and Portland cement >>become if properly used.) > I must be misremembering something my Dad said. I thought he'ld > told me that too much water does not let it cure to hardness. It > eventually falls apart. Concrete is another of those things that behaves differently whenever one gets off the ideal blend with any of the components. As with everything else, a little too much plays into a little determent. When you're talking about too much water then some too much isn't the same as much too much. The two paragraphs above are saying the same thing, you're not misremembering. >>For me there's a clarity issue with the report >>you're citing. > That's true about all the news these days. Today's news reporters are making themselves part of what they're reporting about. >>But then, just how would you explain >>this to the Massachusetts Irish in as few words as >>possible? > Liberals, honey. City slickers who believe that fairy tales are > true ;-). They are what they eat. > That's why I keep wondering why the state chemist wasn't doing > his/her job. I would have assumed that samples of the cement > were taken before pouring. Pre-pour "slump testing" is all there is. There's no test available to determine whether or not the blend is correct or what the cured strength of the concrete is going to be. Post cure destructive testing tells all. >>Even so it did >>take them a while to catch Palumbo in Chicago, [quoted text clipped - 5 lines] >>deteriorated unexpectedly, revealing its >>contents prematurely. > Any bodies? ;-) Who knows. Helen Brach is still missing. But Lake Michigan is h-u-g-e and easily accessible. I think you're more apt to find bodies in the deep parts than under roads. > I just read a bio about Daley, the father. I > knew Chicago was bad but not that bad. You maybe read Royko's biography of Daley? Richard M is a wimp and a wuss. Richard J was a power to be held in awe. To this day the one thing that visitors to Chicago all comment on is how clean the place is, one of the old man's legacies. Richard J has been rehabilitated in the years since his death. It is only a couple of years more till Richard M is mayor for as long a period as his dad was. I think he's been a lot better in the job than those few who were in that office between Richard M and his dad. >>>>>>There are no maintenance-free structures. I understand that many >>>>>>do not agree that concrete makes inspection impossible, but I [quoted text clipped - 21 lines] > >Top down. Yes, they are filled in. They should take sewing lessons. A breach becomes a weak point. Doesn't this happen with bridges? >>>>I don't think that's part >>>>of what we've been calling "inspection". [quoted text clipped - 7 lines] >that doesn't store images but most do. Perhaps not >quite like an MRI though. hmm...I'm trying to picture in my head how a fault can be detected if slices of cross sections of the bridge can't be taken. I guess I'm stumbling over stuff I didn't know I didn't know. >>>>One of last week's >>>>reports of what is wrong with the Big Dig is that the concrete [quoted text clipped - 32 lines] >much too much. The two paragraphs above are saying the >same thing, you're not misremembering. OK. Good. At least some of my memory cells are functioning :-) >>>For me there's a clarity issue with the report >>>you're citing. [quoted text clipped - 3 lines] >Today's news reporters are making themselves part >of what they're reporting about. Yea, I know. What I try to do now is negate what they are saying and then try to figure out why there is a need to lie. I never did think of an answer when Clinton moved his lips. >>>But then, just how would you explain >>>this to the Massachusetts Irish in as few words as [quoted text clipped - 4 lines] > >They are what they eat. Which is all produced by magicians in the back room of the grocery store. >> That's why I keep wondering why the state chemist wasn't doing >> his/her job. I would have assumed that samples of the cement [quoted text clipped - 4 lines] >is correct or what the cured strength of the concrete >is going to be. Post cure destructive testing tells all. JMF's cousin is a chemist. His job is to test the stuff before it leaves the cement plant. Each job has a different chemical construction requirement. I had assumed that, if this can be done at the cement plant, a similar chemistry analysis can be done with samples taken at the pour site. I had assumed that part of the ongoing inspection activity would involve this kind of chemist. But, alas, this would be common sense. Silly me ;-). >>>Even so it did >>>take them a while to catch Palumbo in Chicago, [quoted text clipped - 12 lines] >you're more apt to find bodies in the deep parts >than under roads. Nah. The Lake is too frisky to keep bodies on its bottom. >> I just read a bio about Daley, the father. I >> knew Chicago was bad but not that bad. > >You maybe read Royko's biography of Daley? I can't remember the author and I don't know where I put the book. It was a newspaper guy who had covered Daley's administration. >Richard M is a wimp and a wuss. Is he really? Then who runs him? >Richard J was a power >to be held in awe. To this day the one thing that [quoted text clipped - 8 lines] >been a lot better in the job than those few who were >in that office between Richard M and his dad. I've been reading about the political machines. They did a better job training politicians than what we have now. I simply can't think of a way to instill a checks and balances system in the machines because the successful ones are based on a personality; this is also the cause of corruption (there's no turnover to keep people from becoming entrenched in their little empires they built). /BAH >>>>>>>There are no maintenance-free structures. I understand that many >>>>>>>do not agree that concrete makes inspection impossible, but I [quoted text clipped - 24 lines] > They should take sewing lessons. A breach becomes a weak point. > Doesn't this happen with bridges? It doesn't seem to be a problem. A nice round hole distributes the stresses evenly, and these days they avoid the rebar. >>>>>I don't think that's part >>>>>of what we've been calling "inspection". [quoted text clipped - 7 lines] >>that doesn't store images but most do. Perhaps not >>quite like an MRI though. > hmm...I'm trying to picture in my head how a fault can be detected > if slices of cross sections of the bridge can't be taken. I guess > I'm stumbling over stuff I didn't know I didn't know. Horizontal fractures seem to me to be rare. >>>>>One of last week's >>>>>reports of what is wrong with the Big Dig is that the concrete [quoted text clipped - 76 lines] > kind of chemist. But, alas, this would be common sense. Silly > me ;-). They have a lab at the plant, not reasonable to have in the field to intercept and test every load that arrives and pass it before they pour their load and head back for another. If the state actually wanted to I'm sure they could put an observer (liaison) in the chem lab where JMF's cousin works and just watch over the guy's shoulder when batches destined to their jobs are being checked. There's usually no need to get into depth with this issue. Most providers are honest. >>>>Even so it did >>>>take them a while to catch Palumbo in Chicago, [quoted text clipped - 14 lines] > > Nah. The Lake is too frisky to keep bodies on its bottom. Well weighted down makes excellent fish food. They don't last very long down there, and I don't think bones float real well. >>>I just read a bio about Daley, the father. I >>>knew Chicago was bad but not that bad. >>You maybe read Royko's biography of Daley? > I can't remember the author and I don't know where I put the book. > It was a newspaper guy who had covered Daley's administration. Royko. >>Richard M is a wimp and a wuss. > Is he really? Then who runs him? That's not a given. Little pockets of corruption are prevalent. See the web site for the "Better Government Association" when you're next at the library. >>Richard J was a power >>to be held in awe. To this day the one thing that >>visitors to Chicago all comment on is how clean the >>place is, one of the old man's legacies. >>Richard J has been rehabilitated in the years since his >>death. >>It is only a couple of years more till Richard M is >>mayor for as long a period as his dad was. I think he's >>been a lot better in the job than those few who were >>in that office between Richard M and his dad. > I've been reading about the political machines. They did a better > job training politicians than what we have now. It was an upward mobility issue for machines like Tammany Hall in its heyday. Today's politicians are lacking for nothing when they enter the arena, leaving little to lose if they don't make it (with help) in politics. You just can't keep a guy who has other options in line as you can with a man who has only "this one shot" at being well off. > I simply > can't think of a way to instill a checks and balances system > in the machines because the successful ones are based on a > personality; this is also the cause of corruption (there's no > turnover to keep people from becoming entrenched in their > little empires they built). Glass ceilings also lead to corruption. An individual refused continuing ascent often branches out in other ways to make up for what he thinks he's entitled to but isn't getting. Part of the problem is that the post WW2 generations have been raised to think that upward mobility is another of so many absurd entitlements. Today just about every mailroom kid thinks they'll be running the company some day. The classical "American Dream" doesn't seem to count for anything any more. This is a universal problem, not limited to politics. <snip> >>>>>Even so it did >>>>>take them a while to catch Palumbo in Chicago, [quoted text clipped - 18 lines] >last very long down there, and I don't think bones float >real well. But body parts breaking away do. <snip> >That's not a given. Little pockets of corruption are >prevalent. See the web site for the "Better Government >Association" when you're next at the library. OK. Thanks for the pointer. >>>Richard J was a power >>>to be held in awe. To this day the one thing that [quoted text clipped - 13 lines] > >It was an upward mobility issue Yes. But that trains people. We have senator whose political instinct is 0. >for machines like >Tammany Hall in its heyday. Today's politicians [quoted text clipped - 15 lines] >ways to make up for what he thinks he's entitled to >but isn't getting. And he doesn't end up running the place into the ground. >Part of the problem is that the post WW2 generations >have been raised to think that upward mobility is >another of so many absurd entitlements. Yes. One of my newgroup buddies has observed that the WWII management heirarchy got copied into business after the war because that's what people knew. >Today just >about every mailroom kid thinks they'll be running >the company some day. The classical "American Dream" >doesn't seem to count for anything any more. It does count. The mailroom kids who do end up running their own business are the ones who did the work. However, we are breeding a majority who are taught that no work is rewarded with fame, money and adoration. f.cking Liberals. >This is a universal problem, not limited to politics. It is politics, just in-house? /BAH > >Pre-pour "slump testing" is all there is. There's no > >test available to determine whether or not the blend [quoted text clipped - 9 lines] > kind of chemist. But, alas, this would be common sense. Silly > me ;-). Why would any kind of chemical analysis done at the pour site give any different results from that done at the batch plant? On Aug 27, 7:10 am, moja...@mojaveg.lsan.mdsg-pacwest.com (Everett M. Greene) wrote: > jmfbah...@aol.com writes: > > JMF's cousin is a chemist. His job is to test the stuff [quoted text clipped - 8 lines] > Why would any kind of chemical analysis done at the pour site give > any different results from that done at the batch plant? Less chemical analysis more physical analysis. Things done at the plant: Moisture tests - Verify the moisture content of the aggregates as these numbers are plugged into the batch computer for it to optimize the water content calculations Gradation Tests - Verify the size and weight of the aggregates using screens and scales. Slump Tests - Verify batch plant calculated slump is achieved. Flow tests - Using graduated beakers, verify that if the computer says it just put 300ml of fluid out the valve, that that is really what came out. Things done at the job site: Slump Tests Create Test Cylinders Verify Batch Weights on Delivery Tickets Verify Time in truck. - Most states have a specified amount of time concrete is allowed to have been discharged from the plant to being placed. Say if you are pouring a 300cy pad with a pump truck and you have 4 trucks on site waiting to unload. If the pump breaks down, the last truck in line may not get the concrete off in time. In which case the inspector will reject the load. Producers then will try to use that concrete elsewhere. (Say if it's 5000psi spec concrete for a state load, but it's getting old, it'll work fine in a footing for a house or garage that normally only specifies a 3500 psi concrete. This because if the concrete is old, they will need to add water to keep it flowing which will bring down it's final strength. >> Why would any kind of chemical analysis done at the pour site give >> any different results from that done at the batch plant? [quoted text clipped - 30 lines] >last truck in line may not get the concrete off in time. In which >case the inspector will reject the load. Nice post! Thanks Brian Whatcott Altus OK snip > Things done at the plant: > Moisture tests - Verify the moisture content of the aggregates as > these numbers are plugged into the batch computer for it to optimize > the water content calculations > Gradation Tests - Verify the size and weight of the aggregates using > screens and scales. > Slump Tests - Verify batch plant calculated slump is achieved. > Flow tests - Using graduated beakers, verify that if the computer says > it just put 300ml of fluid out the valve, that that is really what > came out. snip I've cut and pasted the following brief newspaper article because bah doesn't have ready access to the www. Here's a case where all the testing during construction didn't seem to make any difference. Article follows: Posted August 31, 2007 State closes Wausau bridge Gannett Wisconsin Newspapers WAUSAU — The state Department of Transportation has closed the McCleary Bridge on Rib Mountain Drive after inspectors found "unsound material" in three of the bridge’s pilings. The bridge connects Wausau and Rib Mountain. The surprise shutdown occurred at about 4 p.m. Friday during rush-hour traffic at the start of the three-day Labor Day weekend. Police are diverting drivers away from the bridge, which is expected to remain closed for at least a week, said Dan Grasser, DOT regional director. Motorists are encouraged to take alternative routes, including using County R in Rib Mountain to get to and from Wausau if they want to avoid the busy holiday traffic. "Post-construction inspection of the bridge revealed some concerns about three of the bridge piers," Grasser said. "Further inspections identified issues with the footing of pier No. 1. "WisDOT’s first priority is to ensure the integrity of our highways and bridges and the safety of the traveling public, so we’ve made the decision to close the bridge." Divers have been inspecting the bridge this week, and the DOT did not make the decision to close the bridge until this afternoon, he said. Further tests, inspections and possibly repairs are slated for next week. Pheiffer Bros. Construction of Neenah was the prime contractor for the bridge, which was completed in June 2005 for approximately $9.2 million. Grasser said the contractor will be responsible for making the required repairs and it was his expectation that they will move as "rapidly as practical" to make the repairs and ensure the long-term integrity of the bridge. Filed by the Wausau Daily Herald End Article <http://www.postcrescent.com/apps/pbcs.dll/article?AID=/20070831/APC0101/70831179/1979> >> >Pre-pour "slump testing" is all there is. There's no >> >test available to determine whether or not the blend [quoted text clipped - 12 lines] >Why would any kind of chemical analysis done at the pour site give >any different results from that done at the batch plant? Lots of things can happen on the way to the forum. /BAH On Aug 25, 4:15 am, jmfbah...@aol.com wrote: > In article <76c52$46cedb44$49e5dc6$32...@DIALUPUSA.NET>, ... > >>>Lots of north country continues to use salt. ... > >Naw. Ordinary concrete cutting contractors can afford > >the equipment which requires minimal training to use. [quoted text clipped - 6 lines] > Where are these holes made? On the top or from the bottom? > Do they fill them in after taking the sample? I used to work for a Concrete Ready-mix producer in Minnesota. This is how it's done here. It can be different in every state. These are not just holes, they are Cores. They are used to verify the distribution of aggregates and other additives (steel or polypropylene fibers) within the structure of the placed concrete. These core cylinders are then structurally tested by breaking them in a press at a 3rd party lab. (Not the Concrete Producers, nor the Contractors) Concrete Producers also cast test cylinders on site with a frequency up to every truck, or every few hours depending on the size of the pour. These cylinders are kept by the Concrete Producer in a climate controlled lab for break testing after 28 days. Nearly all concrete mixes are specified to reach their designed strength after no more than 28 days. Environmental or manufacturing anomalies can cause the specified strength to not be met within the 28 days. Concrete continues to cure well past 28 days and often the final, stable strength will be much higher than the 28 day specification. State, Federal, and Airport pours require a STATE INSPECTOR at the plant producing the material, as well as at the job site. State, Federal, Airport, and some contractors require manufacturing Batch Weights to be printed on the delivery tickets. Concrete is mixed in batches by weight and volume. The batch weights computed based on the mix design and the qty of product to be produced by the Batch Plant computer system. This system is then responsible for printing the weights on the delivery tickets. This is so the Inspector at the job site can ensure the proper mix design for the particular placement is in the truck that just arrived. Batch weights for all product run through the concrete plant are printed on to a paper report as well as stored in a file that is sent for storage on a central server should any review be necessary. This information is used by engineers at the concrete producer when they break cylinders so they can validate mix design with actual performance. Scales at Concrete Plants in Minnesota are required to be certified every 12 months. > >> One of last week's > >> reports of what is wrong with the Big Dig is that the concrete > >> used to "waterproof" tunnels was watered down. I haven't looked > >> up the chemistry of concrete yet, but too much water doesn't allow > >> the concrete to harden...does it? ... > Oh, not water but other stuff. damned news. This particular > concrete was supposed to waterproof the tunnels. And the word > slurry is a common noun used in the news reports. I don't know > what that is either. Slurry is a term used in Ready-Mix operations to define the "wash water" used in rinsing out the plant or the trucks. Ready-Mix producers are being forced to be more environmentally friendly. In some locations they are required to "reclaim" their wash water. The trucks need to be rinsed out when they get back to the plant, or the plant itself may need to be washed out. Once a truck unloads at a job site, the driver will dump water into the drum to keep any remaining concrete from hardening to the interior of the drum (assuming all concrete was off loaded or any remaining will not be re-used) When the trucks arrive back at the plant the discharge this water/cement/ rock/sand mix into recovery system. This recovery system will extract the aggregate, sand, and cement back into the component parts. Currently the best they can do to extract the cement is to suspend it in the water, producing a "slurry" mix. In some applications (quite few in fact for the producer I worked at due to huge variability in the actual composition of the slurry water) this slurry water can be used as the water component of the concrete mix, and due to its cement content, dry cement added can be reduced. For this to work though, the content of the slurry must be closely monitored as its makeup can change at any time as it flows. > >OTOH while excess water in concrete tends to make it > >cure more quickly and allows easier pouring and [quoted text clipped - 6 lines] > told me that too much water does not let it cure to hardness. It > eventually falls apart. Water increases the heat of the curing concrete as it gives the cement more active elements two work with. The problem is that the water is taking up space in the matrix thus while the concrete may appear to cure faster it actually ends up curing less dense, and thus weaker. The strength of concrete comes from the mechanical bonds between the aggregates and the cements. The right amount of water achieves the best. Too much water and you might as well have not added enough. Note there are admixtures commonly that cause the concrete to act like a high water content but actually has low water content. Say the spec calls for a 6" slump (when using a slump cone filled to the top and tipped over and lifted, the concrete will drop 6" or slump) yet a high strength at 28 days, a 4" slump mix will be used and then an admixture will be added that causes the concrete to act like a 6" slump. These admixtures bond to the cement and restrict curing. With standard dosages, you get about 1.5 hours to get the concrete off the truck and placed before it suddenly becomes 4" slump concrete. These admixtures are quite expensive. http://www.concretenetwork.com/concrete/concrete_admixtures/flowability.htm > >"They sanded down the concrete?" While > >probably true, that description is even worse. Maybe [quoted text clipped - 8 lines] > his/her job. I would have assumed that samples of the cement > were taken before pouring. That is a very good question. I'm sure we won't hear about it in the national news, but I'd like to hear how the cylinder break tests went for those test cylinders. My guess is that either they "forgot" to make test cylinders for those sections, or they "lost" them. When that happens, it almost always will require a core to be drilled to allow for testing. Thank you for taking this time to teach me! >On Aug 25, 4:15 am, jmfbah...@aol.com wrote: >> In article <76c52$46cedb44$49e5dc6$32...@DIALUPUSA.NET>, [quoted text clipped - 21 lines] >cylinders are then structurally tested by breaking them in a press at >a 3rd party lab. (Not the Concrete Producers, nor the Contractors) I had no idea cement can be cored. What kind of drill do you need? Does it need diamond edging? >Concrete Producers also cast test cylinders on site with a frequency >up to every truck, or every few hours depending on the size of the [quoted text clipped - 5 lines] >continues to cure well past 28 days and often the final, stable >strength will be much higher than the 28 day specification. ARe the forms for those cylinders laying down or are they upright? Does it make a difference which way they lie? >State, Federal, and Airport pours require a STATE INSPECTOR at the >plant producing the material, as well as at the job site. State, [quoted text clipped - 30 lines] >Slurry is a term used in Ready-Mix operations to define the "wash >water" used in rinsing out the plant or the trucks. Oh!!!! > Ready-Mix >producers are being forced to be more environmentally friendly. In [quoted text clipped - 32 lines] >taking up space in the matrix thus while the concrete may appear to >cure faster it actually ends up curing less dense, and thus weaker. 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. >The strength of concrete comes from the mechanical bonds between the >aggregates and the cements. The right amount of water achieves the >best. Too much water and you might as well have not added enough. OK. I may have leapt to the wrong conclusion but now some things are making sense to me. THANK YOU VERY MUCH!!! >Note there are admixtures commonly that cause the concrete to act like >a high water content but actually has low water content. Say the spec [quoted text clipped - 5 lines] >dosages, you get about 1.5 hours to get the concrete off the truck and >placed before it suddenly becomes 4" slump concrete. 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. >These admixtures are quite expensive. >http://www.concretenetwork.com/concrete/concrete_admixtures/flowability.htm [quoted text clipped - 13 lines] > >That is a very good question. 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. > I'm sure we won't hear about it in the >national news, And I'm sure we won't hear about it in the local news. >but I'd like to hear how the cylinder break tests went >for those test cylinders. My guess is that either they "forgot" to >make test cylinders for those sections, or they "lost" them. 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? >When that happens, it almost always will require a core to be drilled >to allow for testing. Does every concrete piece of a project have these sample cores stored somewhere in the world in perpetuity? /BAH > Thank you for taking this time to teach me! > [quoted text clipped - 29 lines] > > I had no idea cement can be cored. I guess you missed this when I wrote about it a few posts back. > What kind of drill do you need? A core drill with an abrasive edge. > Does it need diamond edging? 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> >> I had no idea cement can be cored. >I guess you missed this when I wrote about it a few >posts back. >> What kind of drill do you need? >A core drill with an abrasive edge. >> Does it need diamond edging? >Most do though there are those with carbide. One of >the partnered businesses I started refurbishes spent [quoted text clipped - 3 lines] > ><snip> 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 <snip> >> I had no idea cement can be cored. > >I guess you missed this when I wrote about it a few >posts back. 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. :-) >> What kind of drill do you need? > [quoted text clipped - 5 lines] >the partnered businesses I started refurbishes spent >core drills by brazing I need to learn what that means. > new diamond segments to the >spent drill. We currently refurbish from 2 through >24 inch units. 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 > <snip> > [quoted text clipped - 26 lines] > anything about. I can't imagine how you would attach > a diamond to a metal thingie. 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. On Aug 28, 7:21 am, jmfbah...@aol.com wrote: > In article <1188227016.280976.281...@r34g2000hsd.googlegroups.com>, ... > I had no idea cement can be cored. What kind of drill do you need? > Does it need diamond edging? 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. > >Concrete Producers also cast test cylinders on site with a frequency > >up to every truck, or every few hours depending on the size of the > > ARe the forms for those cylinders laying down or are they upright? > Does it make a difference which way they lie? 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 ... > >When that happens, it almost always will require a core to be drilled > >to allow for testing. > > Does every concrete piece of a project have these sample cores > stored somewhere in the world in perpetuity? 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. > On Aug 28, 7:21 am, jmfbah...@aol.com wrote: > [quoted text clipped - 12 lines] > always have a diamond impregnated cutting edge. Expansion joints in > concrete driveways are often cut with diamond edged saw blades. 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 > saws and drills almost always use water as a coolant during cutting. Yes. snip ... > > To get any life out of anything used to cut concrete, they almost > > always have a diamond impregnated cutting edge. Expansion joints in [quoted text clipped - 6 lines] > have the purpose of giving future cracking someplace > specific to go. 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. > ... > [quoted text clipped - 16 lines] > wall, a curb) otherwise the expansion of the slab when heated could > push against things and either move them, or crack the concrete. Thanks. Happens to all of us. >On Aug 28, 7:21 am, jmfbah...@aol.com wrote: >> In article <1188227016.280976.281...@r34g2000hsd.googlegroups.com>, [quoted text clipped - 5 lines] >do, cement isn't cored, concrete is cored. Cement is a component of >concrete. Cement is a powder, Concrete gets hard. 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. :-) >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. Does concrete burn? >> >Concrete Producers also cast test cylinders on site with a frequency >> >up to every truck, or every few hours depending on the size of the [quoted text clipped - 24 lines] >Producer will make the samples if they are trying to validate a mix >design or design change. Do you have to alter recipes from one batch to the next batch to get the same strength? >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. Yea, I assumed that. >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 [quoted text clipped - 3 lines] >slight mix change that isn't noted. Baring any significant problem, >the concrete will eventually cure. I think you just answered the above question. /BAH |
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