It is also, say, the foundation of all western thought since 1900, and it has supported nearly every artist, writer, performer, and us regular nudges since then. (Also, glad to see TOT and his shaking fist.)
Modernity was a mistake. That isn't a dig against steel or concrete reinforcement, it is how it is being used in housing, roads, and other infrastructure to centralize production centers and keep jobs, opportunities, and property rates localized. Commute times are getting longer and the last thing people think is what a marvel their congested roads are.
I retired from a water utility where they had installed a lot of pre-stressed concrete pipe. It looked like a really good idea in the 1960s and 1970s. It could be fabricated to some very large sizes (big enough to drive a car through). Unfortunately, the pipe manufacturer didn't coat the rebar. Keep in mind that water infrastructure is usually installed with expected lifetimes of more than a century. Only a couple decades later, the pipe began to break. Today, the problem is very serious. It's so bad that all pipes of a certain size have fiber optic sensor cables in them. They're listening for the "pings" from breaking rebar. A few years ago, on July 1, they detected a series of seven pings. It was a 94" water main. Crews immediately dewatered that segment and began emergency repairs to dig out that section and replace it. Water supplies were shunted to an older 48" main. We survived the July 4th holiday with the very good fortune of not having any house fires. Thankfully due to reduced demand and dumb luck, we got the repairs done before anything bad happened. We were concerned that some places in the service area might not have sufficient reserve water for fighting a large house fire if water demand was more than typical. Later, when the pre-stressed concrete pipe that was removed from service was examined, they found seven breaks in the rebar where corrosion had compromised it. Had it been left in place and allowed to break, it could easily have washed out several buildings. This is something we really need to get right, or there will be terrifying consequences.
I'm trying to imagine how much water a 94" pipe can transport. If it blow out completely, it would be like having a river flowing through the backyard.
Awsome. I couldn't agree more with your statement, "many disasters have come to due to lack of maintenance rather than lack of design..". As a person in the maintenance field, i can appreciate that statement.
Hey Stars, how long does it take concrete to erode and be dangerous. We have a concrete beam and it has been exposed to rain for 12 years with some rust on the rebars. Is it dangerous?
well look at google streetview and map. They have been building a new structure next to it much closer then the original building they demolished. So it is possible the concrecte got damaged because of the new work done there. It happened before.
@@klaasj7808 That’s unlikely. The latest reports suggest that the culprit was poor maintenance over many years, which allowed prolonged flooding of the basement, which most likely caused the same sort of corrosion described in this video.
@@MarcosElMalo2 maybe both, when it was already poor and new building arises accomplished with heavy machinery then this whole process went even faster. dont say they did anything wrong next door, as they couldnt know.
I have seen concrete placed in these conditions. During the concrete placement the contractor will have a crew member with a hooked piece of rebar. The hook is used to lift the rebar as the concrete is placed and then consolidated with a mechanical vibrator. On a side note, the yellow Stego Wrap (15mil) vapor barrier is another technology used to help protect the concrete from the corrosive soil and gas in which it is built upon.
There is no point at putting the rebar where the concrete will compress. And if you are pouring a slab for a house or garage it should have a vapor barrier under it.
@@nosadonions3231lifting with a hook or a rake is not the same as implementing correct cover with chairs. I've noticed that many American concrete placing professionals don't really understand the purpose of rebar. It's not just reinforcement it's tensile load bearing. Each bar has an optimal position in the concrete element.
One of the reason the process you mentioned is avoided in Civil Engineering is because the proposed system give less visual cue before failure happen. The new concrete mixture you mentioned failed at around the same load level as regular reinforced concrete, but it doesn’t reform like regular reinforced concrete. This make it difficult for inspector and give little warning before in failed. One of the lesson I learn at our concrete course is that’s don’t over-reinforced concrete, which can create sudden failure. We want to design it a way that before concrete failed, it give enough visual warning so inspector or normal people can catch it and evacuate. The new mixture give less visual warning to inspector. It might prolong the life span of product but it might create more dangerous condition if doesn’t use it accordingly.
The first enemy of reinforced concrete is moisture and water coupled with the subzero temps during winter. When water makes its way in minor cracks it reaches the rebars starting the oxidation process.frozen water expands cracking and literally destroying the cover concrete exposing parts of rebars. Here in Italy in front shore building we use hot galvanized rebars, coupled with additives on the concrete making it water proof. A galvanized rebar is basically eternal . Obviously costs skyrocket since the rebars are sent to the galvanizing facility .
The problem here is a shear failure for all three beams without shear reinforcements, so it breaks suddenly as it is a fragile response. In fact fiber reinforced concrete does show very large cracks before failure but not at the service state, so you know that when fissures can be seen in this type of concrete you can assume that a failure is at risk.
If the use case was a single family house single story foundation. I wonder if Would failed here be less catastrophic and benefits of longevity more valuable?
@@3dvorator come see Canadian highway bridges where salt is used heavily in the winter. I can assure you hot dipped galv rebar is far from eternal. 10-20 years maybe before you start getting higher maintenance required
@@coadycarter9230 we use galvanized brackets on floating dock ( which floating tanks are actually reinforced concrete built ) and they stay submerged in salt water decades. 🤷♂️🤷♂️👍👍
At London Heathrow airport we had a serious strength problem with the concrete being laid for the then new Terminal 5. A new concrete mix was being used that was much stronger than previous formulas. It could be laid faster and thinner with significant savings in time and cost. It was a good candidate to be used for any new apron/runway works elsewhere at the airport in the future. Specimen slabs were taken from every pour, and tested at 1 month, 2 month and 3 month intervals. Then, many months into the project, and with less than year to opening, specimens started to fail the strength test. It was very puzzling as the constituents seemed to be identical those in the specimens that passed. This was a major concern as it could be very costly, especially if more concrete had to be ripped-up and re-laid. The detective work turned-up a surprising result: One of the ingredients was fly-ash from coal-fired power stations. It just came in on a contract from the power company. The main source power station had been shut-down for summer maintenance and the source switched to alternative power station without our knowledge. The fly-ash was chemically identical but it was ground more finely - and the more finely ground fly-ash absorbed more water, and concrete made from this wasn't as strong! Once this was discovered the problem was quickly resolved and concrete strength restored for subsequent pours. And Terminal 5 is one of the finest airport terminals I know, and one of the most interesting projects I've worked on. (My involvement was in managing overall project risk and, as a physicist, had no connection with the concrete laying activities.)
Wrong question. Steel does indeed rust. Steel used for reinforcing concrete MUST BE COATED TO PROTECT AGAINST RUST. Concrete is ALWAYS WET enough to cause rust of any steel that contacts it. Most contractors go through life lying, stealing and cheating - they must be republicans. Corruption in the building industry is a way of life for... oh you get the point.
@@Tanmay.Patil1 Yeah as much as I am for pointing at a political party opposite of my own, this is one of those instances where I can't pin politics on it in anyway shape or form, despite the ways we can point in that direction. This one is really between the owners/managers of the property and possibly the contractors. I'd leave the conclusions up to the investigators.
@@Tanmay.Patil1 Maximizing profit over saving lives goes hand in hand with conservatism. Conservatism is absolutely the reason there is inadequate regulation overseeing building maintenance that would have saved those 100 people. The conservative mindset- individualism, the aversion of regulation, taxes, HOA fees, and a lack of care for the public- is directly what got those people killed. Check what Ron Desantis has said about the collapse. It is absolutely a political issue.
Good stuff. I'm not an engineer, but I have been involved in the construction trades for my entire working life. I enjoy your vids because the are informational, technical, factual. There is so much anecdotal evidence and misinformation to deal with in the trades. In this instance, concrete legends and lore. I hate hearing "Add five gallons". "Add ten gallons." Right, slop it up to make it easier to place, wait longer for it to set, break it out when the test cylinders tell the truth. Grrrrr. Before a pour, I go to the concrete supplier, meet with their engineer, discuss our expected result and our site conditions and their recommendations. "Oh! They're trying to jack up the price per yard!" B.S. They aren't dummies. Their continued success depends on satisfied customers and word-of-mouth. They know much more about concrete than I do. I'm going with their recommendations. Side note... We were pouring a slab 36" deep. 100'x25'. The crew and I formed it up, installed rebar, etc. We scheduled it for the following Monday. Over the weekend, the weather forecast called for -0 degree temperatures Monday night and into Tuesday. We tented the area, heated it, and went ahead with the pour and then insulated it. The engineer for the concrete supplier came out Monday morning and stayed on site until the pour was complete and insulated. He even brought out several pairs of Ninja cold weather waterproof gloves. What a heck of a good guy. Work with and trust the engineers.
The last line is imperative to good construction work. If you're petty and too stubborn to work with someone that might know a bit more about something than you that's when problems start.
I just found this channel a few days ago when it popped up in my suggestions on YT. I've been a bridge inspector for over 20 years, so little of the concrete series is new to me, but still very interesting and I've surely learned a couple things I'm currently on a major new bridge construction project with a staff that has not had much bridge experience. I am certainly going to recommend that all of my staff subscribe to the channel. I began my career as a surveyor in a small surveying/CE firm in the mid 70s. Before too long, I was in the office, designing subdivision roads, open channels, culverts, sanitary sewer collection systems, etc.... all of this without benefit of education beyond high school. Your Civil videos add background to the things that I understood only logically those many years ago. To any viewers of this channel that find this stuff interesting, I can only add that... "I wish I'd paid more attention in my math classes!"
As a LEO, I have no background in civil engineering or whatsoever, but somehow after watching almost all of your videos i know pretty much the basic of how some things work. Thanks for sharing your knowledge with me dude, hope your channels keeps growing bigger than ever before!
Why do we use steel? It has a thermal coefficient of expansion almost exactly the same as concrete. This has been called "the single physical fact that contributes most to modern architecture".
We use steel if you want to consider dead loads as a critical function in design (as a steel beam is almost always lighter than a concrete (even prestressed) girder - for the same design capacity). You might also consider steel if a primary load carrying member is curved. Otherwise, PS concrete and reinforced concrete is an efficient design approach.
While the thermal coefficients are similar, both materials don't necessarily adapt to temperature changes at the same rate. The physical fact that chiefly contributes to concrete and steel working in a compatible manner actually seems to be the adherence between them. And definitely one of the greatest contributions to modern architecture, of course.
Hahaha, I was coming down to the comments to say pretty much the same thing as soon as I saw the fibre reinforced concrete! XD Plaster and horse hair is another old one. The ceiling of my old bedroom had almost an inch of that on wooden slats before it all came down
@Kiritsu - Actually some of the oldest man made structures are made from granite and basalt stone. Examples: The Pyramids, the megalithic walls of Peru, and so many others around the world. These structures have endured for many thousands of years. Who made them? How where they constructed? No one knows. :)
Interesting that Google is recommending this to me today: The experts are saying that 'Salt Oxidation, via Concrete, of Rebar' was likely involved in the Surfside Miami building collapse.
I live in Florida and you see a lot of old condos from the 50s, 60s, and 70s along the beach. I often wonder how long the rebar in the floors can withstand the salty air. There is one in Cocoa Beach where the floor is visibly sagging above the carports.
@@CASANOVAPRO1985 yes I love in nova Scotia some concrete right on the water will get really brittle get big crack some you can break off with your hands
Dad was a rodbuster and I spent many a summer working for his company packing and tying steel. It is likely that humble background that caused me to get my engineering degree and complete a 30 year career in the business.
There was an interesting case in Soviet Russia with Luzhniki Metro Bridge in Moscow. It's a double-decked concrete arch bridge and It was built in the late 1950-s and in record times, about 19 months. To speed up the construction and to be able to continue pouring concrete during the Moscow winter they used salt in the mix to make sure concrete can properly cure at -10C/14F. The bridge rapidly deteriorated and had to be partially closed down only 14 years later.
@@FablestoneSeries Practical Engineering has a video on that exact topic of why Roman concrete is not better than what we have today. First, there is no good reason to spend the time and money (taxpayer dollars) to build something that lasts thousands of years when it really only needs to last a few decades before it is torn down for something better or to meet new demands of being built somewhere else. There is no reason to build a road or bridge that lasts 1000+ years when cities are created or are abandoned over the centuries, when routes need to be changed to meet different traffic demands, when bridges/roads need to be torn down or rebuilt for environmental reasons, and even rivers change their patterns every few centuries. So those surviving Roman structures are overengineered and impractical in terms of cost-effectiveness and are not flexibile enough to meet changing needs. Second, outside of PE's discussions, there is survivorship bias where only the best built Roman buildings (their best civil engineering projects) survive to this day while the vast majority of average or lower quality Roman buildings have crumbled/disappeared. For example, you typically don't see any Roman apartments or regular Roman house from the Roman era survive to this day even though they were the most common type of building. Third, Roman buildings such as the Roman Pantheon were actually in continuous use through the middle ages, so they were continuously maintained and repaired.
@jeff mattson Practical Engineering has a video on that exact topic of why Roman concrete is not better than what we have today. First, there is no good reason to spend the time and money (taxpayer dollars) to build something that lasts thousands of years when it really only needs to last a few decades before it is torn down for something better or to meet new demands of being built somewhere else. There is no reason to build a road or bridge that lasts 1000+ years when cities are created or are abandoned over the centuries, when routes need to be changed to meet different traffic demands, when bridges/roads need to be torn down or rebuilt for environmental reasons, and even rivers change their patterns every few centuries. So those surviving Roman structures are overengineered and impractical in terms of cost-effectiveness and are not flexibile enough to meet changing needs. Second, outside of PE's discussions, there is survivorship bias where only the best built Roman buildings (their best civil engineering projects) survive to this day while the vast majority of average or lower quality Roman buildings have crumbled/disappeared. For example, you typically don't see any Roman apartments or regular Roman house from the Roman era survive to this day even though they were the most common type of building. Third, Roman buildings such as the Roman Pantheon were actually in continuous use through the middle ages, so they were continuously maintained and repaired.
I'm experience, not an expert. with that said, no wonder it failed. The temperature alone will cause it to fail. The salt didn't help the curing process, it only hurt it and made it cure weaker. Salt won't make the cement get warm enough at that temperature, calcium chloride will but even then it will still cause corrosion and can make it weaker.
@@Intranetusa I'm seeing a debate by me about replacing a bridge that is 100 years old. There is so much debate about it that the only way it's likely to get replaced in any sort of hurry is if it actually breaks and causes a major traffic disaster in the process. I would say that's a great argument for building a bridge that could last a thousand years. People refuse and wait to change things because they're stupid.
An official of Surfside, Miami stated, “We are all scratching our heads asking how this happened? “ We know how it happened. We have the science..its explained here pretty clearly. Bad design, building and maintenance.
@@EricDMMiller Harsh words. Harsh... but true (minus the good riddance part). Clearly, they did not have a clear understanding of what they were (not) doing. That is not the engineer's fault - records clearly show that he strongly advised immediate remedies in 2018 - but it does shine a light on important part of human psychology. They must have read the words, but they didn't take them to heart. "It will be fine. Surely it can't be _that_ bad. This can't be happening to _us."_ Similar disasters elsewhere has seen off-site owners vilified as uncaring or even speculating in the collapse of a building. That might sometimes be the case, but even the most callous of developers will realize the trouble they're in when I building they are responsible falls down and people die. I think a far more likely explanation would be same kind of magical thinking displayed by the people living in this complex. So that leaves us with the question: what facts am _I_ ignoring based on wishful thinking and internal appeals to incredulity?
Hey Grady, Thanks for putting together these videos! You have a way of explaining things in a straight forward manner, without the "I'm better than you" attitude that most engineers seem to learn in college.
The intro "Hey I'm Grady..." and you know you are in for a learning session.. Well presented and all the tech info is clearly explained and demonstrated. I am a gas engineer and love Grady's practical engineering channel. Its taught me many aspects of other engineering fields. Great channel, thank you Grady for your hard work and enthusiasm.
I would never have believed that I could sit through successive videos on civil engineering and be fascinated throughout, yet, here I am again, having watched yet another clear and engaging video. Good on you, Grady! 👍👍👍👍
This might come as a surprise to alot of persons. If you pour concrete over slightly rusted steel members, the abrasion between the mix and the rebars actually removes most of the rusting in the surface of the rebar. Discovered this some years ago while doing a demolition on a floor slab I casted years prior, the rebars actually appeared brand new out of the factory.
I always found it weird the Metric System would have a unit that's pronounced the same as a similar Imperial unit. Why not "megagram"? Mega is a viable prefix and grams measure the same thing (mass).
@@foxymetroid Um, I don't know if you're joking or you're playing a smart ass... but Tonne actually IS correctly called a Megagram. That's the official name. If it was just a lucky guess on your part, well, you're right! :)
@@foxymetroid Ton/Tonne isn't originally imperial or metric. The name comes from an old measurement of volume called tun, basically a standard-ish wine cask, eventually turned to general expression of something being very heavy (I.e. "it weighs [like] a tun"), turned to sort of a unit of measurement. The full cask would weigh about 950kg or a wee bit more than the 2000 pounds of a US ton. Basically, it was a parallel development with people being people and just kept using the word, made it more precise to get on with the times by merely rounding it down/up to a nice number that made sense in the system they used.
I constructed and maintained bridges for the state of SC for 34 years. Although some of the bridge beams we used were not of the best quality due to poor quality control at the beam plant, most of our problems came from lack of maintenance, When I would make complaints to management, I would get answers from the SCDOT top manager that the public did not see the underside of the bridge. What he was trying to say was the money for proper maintenance was not there and we would have to do our best with what money we had. I would get really pissed knowing that I was spinning my wheels trying to keep the bridges in my district from falling. Some are really in bad shape and only get money for repairs when the inspectors rate them critically. Not only were some of my bridges state-owned but interstate owned by the Federal Government. Many of the major repairs I did were bridge bearings due to lack of maintenance. Many with stress cracks from bearing failures. I could go on with problems I tried to repair but money is a key issue. It is expensive to make repairs to bridges but the flowers alongside the road look much better for those in authority.
Sir, who creates the money problem ? The govt. authorities or the private company for which you were working. Why would be there shortage of funds from govt. side as it's all public money and US govt. has most money on planet.
As said by a US Senator: infrastructure is boring. Also, the attention they get from maintaining infrastructures is not as much as creating new ones, so there is that.
@@SurajSinghTomarArya The "Free Lunch Anti-Tax Republican Party." They don't want to pay a single tax, but still want America to be the best, baddess, and meanness Country on earth, ... for free.
Raymond Myers uh no. In SC they just put through doubling registration fees for vehicles, license fees and taxes in new vehicles to “fix the roads”. The only roads being fixed are interstates. Secondary roads?😂😂 I do hope if you visit SC (where I’ve lived all my life) you did pay a little extra for the struts with coil springs on your car or truck. We’ve just gone through the wettest winter on record and the potholes are abundant. The only good thing about them is it does slow traffic on our road which usually is flying (two lane road) shoulder in some places, others ?? We already were paying some very high vehicle taxes before the incremental doubling went into effect. The money is going somewhere but not into asphalt on secondary roads. The interstates will be masterpieces but getting to them will kill your vehicle. A road near us was “resurfaced” recently-sprayed with tar and pea gravel spread on top and a ditch reshaped on one side near an intersection. I have seen four cars, two pickups, and one tractor trailer stuck in the ditch because if you swing wide to make the turn, the new ditch starts at the edge of the asphalt. Zero shoulder. None. When I say stuck in the ditch I mean the cars passenger doors were on the bottom of the ditch and the people driving had to stand on their consoles to open the drivers door nearly straight up to get out. Who in their right mind signs off on these projects when complete?
you know i never saw myself doing engineering until quite recently in my life, it's so much more interesting than I thought! I'm really glad there's channels like yours
If you came here after the surfside collapse.... thank you for wanting to understand and learn! The world needs more people like you, in order to grow as a whole.
Brilliant, thank you. My 2 brothers and I were raised on a diet of all things concrete as teenagers. My poor late father purchased a manual block maker and we spent 2 summer holidays making our own 6in concrete blocks using semi dry concrete that we mixed ourselves. Approx 20 blocks a day, not for the faint hearted. We thought we were great, what a great experience, thanks to our Dad. We have since seen lots of rebar used on other jobs round the farm, and my concern has always been when will that rebar rust!!! I really enjoyed your video, thank you again, my youngest twin boys now 16, are keen to follow up some form of engineering at university hopefully. looking forward to more videos.
A Carragher, good familie experience on your farm. But make a block ist a simple think, make a concrete roof is an other think, tha is the problem. Dont make your own roof with concrete, without a good advice(Spezialist). realy no es very complicated, but the details are important. No es nesessery go to HIGHSCOOL fore that Job, ist nessessery open your eys and ears and understand what means work like a man in the field. A man can do everthink, today take a laptop and google around, make some experiments on your farm, and go on. Concrete is a beautifull Material, cheap, but need a strong man , to dominate the Concretemix, like a devil. Ever low water, the rest go hard ike a stone alone (28 days), and the construktion is your own. Go ahead, young Boy, the time is running away, and nothing is done. When you make fenceposts , dont put steel inside, the steel will brake the post, better more thick the post, little bit more concrete, better result. The Concret devil i
3:30 "he did it in another video" but he stated it was only briefly and would like go into more detail into in subsequent post. BTW some of the things he say is miss leading... And y Dang! it not cool to look at past posted vids? lol
Incorrect, he states in this vid it was "pre-stressed" not post-stressed rebar...And if the rebar is freefloating the issue of it being pre-stressed vs post-stressed is a mute issue.....
Hi Potchi! Concrete does not actually dry like a wet towel, by evaporation, to become strong. The water molecules reacts with the cement in a process called hydration. So the water actually stays inside the concrete forever, and therefore, concrete may also set underwater. A more common problem is that the concrete is evaporating water in hot conditions, making the finished product have a rough or cracked surface, and that is why newly poured concrete is sometimes sprinkled with water. I am not a chemist and haven't thoroughly read up on the subject but I hope I was of some help.
Nothing special for "pour" concrete underwater. You need form where it will be pumped and pumping will start from bottom and keep hose there until form is filled concrete pushes water away when form fills and that way only top part of concrete touches water and rest remain pristine. That top part is sacrificial layer and isn't include part of designed structure meaning if you need 10"x 10" and 3 feet high footing example for pier form needs to be like 1 foot taller because that top layer becomes weaker by touching water.
One of the reasons why you don't very often see stainless steel rebar (or other alternatives) in concrete is because some of the most common stainless steel alloys have a wildly different thermal expansion ratio. Meaning that if your reinforced concrete cools down or heats up, the 2 materials will expand at different ratio's which causes cracks of its own and a range of other issues. Concrete and good old steel are pretty closely matched however, meaning that cracking due to thermal changes is pretty much a non-issue.
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The alleged corrosion resistance of stainless steel is dependent on exposure to oxygen, which causes stainless to form an oxide surface that protects against rust.
The range of properties for SS is due to the fact that "stainless steel" is not a well defined term. There are a variety of approaches to getting steel not to rust and these are all generically called stainless steel though they have very different physical properties, based upon which other elements are added. ASTM does create(validate) various standards but the real reason why stainless hasn't caught on is cost, strength, and most importantly !!!!BY FAR!!!!! is ductility. Good old fashion steel will stretch but not break, the perfect building material. Adding more carbon, nickel or chromium might increase some desirable properties but it also makes the steel more brittle. The worst property possible when parring to concrete.
I love this channel and the way you explain civil engineering concepts is excellent. Our society is abundant with engineering marvels, it just needed someone like you to explain it to the common man for them to appreciate it's value. Thanks a lot!
This video is an excellent basic teaching of concrete and steel rebar. 2 weeks ago ( June 2021) A massive 12 story Condo in Florida located close to the ocean collapsed. It's easy to see NOW how salt water can corrode the rebar and cause deterioration.
It's a sad fact of our industry that an engineer talking about concrete cover can't find stock footage of a slab being placed with the reinforcing properly supported on chairs.
The Essential Craftsman channel has some good videos of proper concrete reinforcement and form set up. He walks you through the process on doing a few different projects, including a heavy retaining wall for site prep for building a house. It is a great channel for learning about the construction trade. He is also completely insane with his skillsaw skills. I am talking ripping a 2x4 to have a 45 degree bezel on the edge freehand type skills. Serious DO NOT TRY sort of stuff.
My experience in the building trade for more than 50 years when I have seen concrete breaking away from a building it was because the rebar was too close to the face of the finished concrete.
A very interesting topic, thanks for posting. I watched because in 2021 I had this exact problem. My 123 year old building has a roof made of reinforced concrete that was poured in place. The total thickness of the roof is only about 3 inches, so there is no cover. A section of the roof collapsed. Thankfully, no one was seriously injured. A roofer was on top at the time, and fell about 20 feet, but bounced of several pips and pieces of equipment on the way down, and only had burns and bumps and bruises. The entire roof will be taken off in the spring, and replaced with steel deck.
Impressive, given the fact that the first commercial uses of reinforced concrete were only made in the 1870s! So your reinforced concrete roof from 1898 was actually a museum piece, you were lucky that it didn‘t end up on any list of protected monuments, that would have sucked as far as renovation constraints go.
@@armincal9834 It's a business, and it's a beautiful old building. There are postcards of it floating around, one from 1926, and another from the 1950s, so maybe it should be considered a historical building.
Grady, you hit the nail on the head with the last 30 seconds. If agencies do not program the proper maintenance money, all the innovations are for nothing. We use HRP in concrete in concert with the FRP and CFR/Glass all that will do is to delay the cracking. This assumes the mixing, placing and curing is done per ACI and local specifications. Great thumbnail sketch of the problem. Keep it up.
I know of a garage that had a concrete floor poured with steel fibers mixed in. Worst thing they could have ever done. As mechanics, they need to lay on the floor to get under cars and such. As the concrete wore away from constant traffic, the steel fibers began to poke though the surface and would constantly catch on their overalls and poke them in the back. Not fun.
Unfortunate, but the concrete isn't entirely a mistake here. A surface coating of epoxy, enamel, or some other hard material could easily salvage that floor and ensure it lasts many years to come.
They make concrete sanders. I would just run one of those over the floor. But seriously concrete shouldn't be wearing away just from rubber contact. Sounds like a bad concrete installer all around
Thank you Grady, your work and enthusiasm for engineering continues to impress. I hope everyone out there is inspired to find a job they love (and allows them to play with awesome toys.... er, serious testing equipment for the sake of science)!
I've loved fiber mesh since I learned about it 30 years ago working at a concrete company. Problem is most suppliers don't encourage it. Often they say it doesn't really add any strength. I've explained it's about cracking, not strength. But the added couple bucks per yard just stops most people from using it.
Fibre has a remarkable effect in stiffening up the concrete mix (you can see in the video how stiff it gets). This makes placing the concrete much more difficult, in particular ensuring that the concrete flows all around the reinforcing without leaving voids. Which in turn means that much more labour and care are required in construction. No such thing as a free lunch.
This video perpetrates an old wive's tale and reminds me of when I attended a civil engineering unit at university 40 years ago. Part of the unit was conducted in the civil engineering lab by a crusty old technician. He began the session by asking us which is stronger in tension - steel or concrete? Many chaps answered "steel" I don't remember any students picking concrete. The tech/lecturer sort of nodded slightly and then asked which is stronger in compression - steel or concrete? Chaps answered "concrete". He then sort of smirked. He then proceeded to demonstrate the strength of various concrete cylinders, about 250 mm long and 200 mm diameter, which we students had made the previous fortnight using various mixing methods. He put each one in turn in the hydraulic press and wound up the load until each concrete cylinder cracked and failed. They all failed well below the capability of the press. After discussing that care in mixing made a big difference in strength as shown by the test, he repeated his first questions: Which is stronger in tension - steel or concrete? In compression? The same students gave the same answers. I was looking at the hydraulic press, and realised that its jaws were made of steel. So I said "Steel is much the stronger, in tension AND compression". The tech/lecturer thereupon said "We've broken the record. Only one student this year can think. Usually I get 2 or 3." [Compressive strength of mild steel is around 580 MPa. Concrete is 20 to 40 MPa] Why do we use concrete? Because it's real real cheap compared to steel and just about anything else, and it's rigid. Folk don't want wobbly buildings. Why steel reinforced concrete? Because when overloaded or not properly made, it cracks, warning you, doesn't fail catastrophically without warning, and is fireproof. Concrete by itself fails catastrophically without any warning. In the 1920's and 1930's a lot of city buildings were built with steel frames. When they caught fire, the red hot steel lost strength and the buildings came down, usually upon next door. Concrete is a good thermal insulator - if a steel reinforced concrete building catches fire, the fire brigade usually has time to turn up and get control before it collapses. City fire brigades don't actually care much if a building is ruined by fire. But its a nightmare for them if the fire spreads to adjacent buildings and then more buildings. That's why regulations and conventions make buildings not so much resistant to catching fire, but resistant to collapsing.
Steve P I can no longer go on road trips without noticing the the beautiful and large amount of engineering involved In Overpasses and even inclined terrain. Whenever I had the niece and nephews in the car in the past we would talk about all sorts of Science and technology topics, now after following the channel for quite some time I can now incorporate some engineering. Now I just have to find a way to make math a little more fun and enjoyable for them!
I worked at Redland Bay Golf Club, near Cleveland, Brisbane, Queensland, Australia. During WW2, it was an American Military Base, and they laid down some concrete pads with massive twisted, flat reo bar for large generator use I believe. We ripped it up to build a new machinery shed next to the clubhouse, and there wasn't a spot of rust or corrosion otherwise on the reo bar after some 60 years.
I first learned about rebar corrosion years ago when my wife and I visited what had been for years our favorite Daytona Beach hotel. The Americano Beach Hotel. We first visited in about 1967. I think it was brand new or relatively new at that time. We went every year for ten years but then moved on as our careers developed. Years later we went back and found that they were selling time shares as they were rebuilding the structure. We knew nothing about time shares but my wife wanted me to learn more. As I looked through the new rooms being reconstructed the first thing I saw was the construction taking place and the corrosive problem with the rebar and deteriorating concrete. I remember one guy actually pointing to a piece of deteriorated floor concrete and rebar and telling me about it. People I talked with said the repairs were not sufficient and wouldn't last. We never went back. I subsequently learned that the hotel was hit by a hurricane and is(or was) no longer habitable. When I saw the damage done in Miami, my very first thought was corrosive rebar and damaged concrete. My guess is this property is only one of many in Miami with a problem. I've seen properties built and rebuilt there without much control. Miami will cost billions of dollars to be rebuilt. Many of those retirees will loose everything they have. Government officials will most likely walk away unscathed but some are responsible for this fiasco."Due diligence".
Local government officials come and go. Often when someone new gets elected they replace staff. That is why you need Federal and State Standards/Mandates that local towns needs to abide by, otherwise you will see this continue to happen. But even then there are thousands of zoning laws that on the books that aren't enforced (until a property is sold and needs to be inspected).
Steel reo also adds ductility to a structure. Ductility allows us to design predictable load paths as well as reducing the risk of sudden failure. Additionally Steel has a nice predictable elastic deformation until yield allowing it to recover its initial shape after a load is removed. Finally another tactic to reduce corrosion is to limit crack widths. Small cracks, often as a result of thermal shrinkage can self heal because any water that infiltrates them tends to activate the calcium in the concrete matrix sealing the crack. As the cracks get larger the effect of this property drops off.
I’m in concrete repair/restoration. The fiber and steel additives are mostly used in shotcrete and gunnite applications. You should also look into cathodic protection systems, we implement these to almost completely negate corrosion in some cases. There are many different systems and it’s very interesting.
This explains the issue I'm having on my 9 year old driveway. The expansion joints have rotted out and, upon taking the wood out, I've discovered rebar run through them and frequent cracks in the concrete where this rebar goes through the expansion joint wood. The rebar has rusted inside the damp/rotted wood, expanded and cracked the concrete at the edge of the expansion joint.
Yes you can tell because of the 45 degree angle crack which is shear failure. He should've pressed in with the machine on the direct center of the beam where the positive moment is highest is he wanted to test the tensile strength better imo
Done that text with a similar set up in college with a non reinforced beam which is the accurate test for shear on non reinforced... haven't tested reinforced yet tho so that's my 2 cents
When i was helping with research work at my university, one of the research projects being worked on was the use of a steel mesh reinforced polymer wrap to be used on columns as a replacement for rebar or for repairing existing ones. it removes the necessity of form work and is great for marine or highly corrosive environments. (the research project i got involved with was the use of steel fiber reinforced UHPC for steel bridge girder repair.) i was shocked to learn how much time and experimental effort goes into proving and implementing new tech and methods in the construction industry,
“Durability is as important to public safety as other design criteria.” How true. The trick is to try to convince industries of this at a time when profit margins are everything.
People complain about profit margins, but its the only reason all economies even work in the first place. The system has to produce more value than it consumes in order to justify its existence. All companies in said economy have to have a revenue stream greater than their cost stream or they eventually run out of resources to operate. If all companies in an industry (or all industries in a society) have less revenue coming in than going out, the whole system turns into the Soviet Union and collapses. As economist Thomas Sowell pointed out, "There are no magic solutions. Only trade-offs." You want the highest quality stuff? That is going to cost you a lot more than a product which has its quality balanced against its cost. The disaster that was Chernobyl in the Soviet Union was caused by the same drive for lower-costs that you see in other economic systems (they chose graphite tipped control rods instead of the West-standard boron control rods because graphite is cheaper), and they had to have the cheapest costs possible thanks to systemic dysfunction caused by lower worker productivity, due to workers not working harder to get more income, as you would get the same pay in an egalitarian communist system regardless of the quantity and quality of work you did. This lead directly to a regressive feedback loop of workers productivity dropping as they saw no reason to work for more than the minimum to get the same pay, and since the cost of not working was spread out over all workers, a slowly growing pool of workers dropped down to doing the bare minimum they could get away with without being shot by overseers/guards or shipped off to force labor camps. Unlike private companies which can be sued for bad practices in the West, the Soviet government (which owned everything) didn't have to care about safety standards because Soviet citizens couldn't sue them for disasters caused by them.
@@GreyWolfLeaderTW, you mean this Thomas Sowell? “Electric cars may be fun at amusement parks, where they don’t have to go very far or very fast. But if the consuming public wanted electric cars for regular use, Detroit would be manufacturing them by the millions. Only people infatuated with their own wonderful specialness would think that their job is to coerce both the manufacturers and the consuming public into something that neither of them wants.” I have always found his views simplistic and informed by a far right ideology. The passage I’ve provided is evidence of this tendency. The data on advancements in electric car technology prove his views to be incorrect. As for this subject, civil engineering has a social responsibility. The internet is replete with examples of how this is achieved. I will not address the straw man fallacy you’ve presented. Providing an extreme example from a failed state bears little relevance to the discipline of engineering in a fully functioning democracy.
Thanks for your whole series. My son is an EE (Purdue) and that field seems the queen of engineering. Your series shows not so! For me you have taught me the big difference is scale: timescale and physical. You show CE works at huge physical scale as well designs that must perform over decades while having to deal with the interactions of disparate materials. These are lovely TH-cam videos. Also, you show me I mix my concrete way too wet! Keep up the great work!
I always find it interesting how old concepts are reused to make them new again. Wattle and daub was one of the earliest methods of building walls, used for at least 6,000 years. The wattle was basically like a wicker basket, bits of wood or sticks woven together to form a scafolding. Then the daub was applied, made of mud, sand, clay, and most-notably... straw. The straw in wattle and daub provided the same function as the fibers in reinforced concrete. Reinforced concrete itself is very similar in concept to wattle and daub... Only steel instead of wood, and concrete instead of clay and sand.
I think it should be mentioned that while visible cracking of the concrete shown in the video is decreased, micro cracking (which will allow water incursion) is still happening. Concrete needs to be protected by a hydrophobic additive, sealing (paint, waterproofing e.t.c) or other means of long term care if uncoated reinforcing steel is going to be used in harsh environments, especially those that involve salts and standing water.
When my dad made his home, he used concrete mixed with straw, rocks and rebar dipped in old engine oil. Don't know if you can do something like this today but this was 50 something years ago in the northern part of romania (summer+35, winter-25). he isn't here anymore, but the house is ...
@@ThomasSiebenhofer Thomas Siebenhofer back then they didnt have fiberglass (well, they did but they could not get it because of Ceaușescu) so they used straw whitch has been used in mud huts in africa since the dawn of time and is increbily effective. not as effective as carbon or fiberglass but still better than only concrete. update, I went back to my fathers home in 25/01/2020, needs a bit of work on the roof but the walls are perfect.
@Plutarch the inspector would fail it because it doesn't fit with the standard not because it doesn't work. The role of the rebar network in a building is to defuse the tension (vibrations) all over the structure. In fact in Holland you'll see many walls made up only of (stainless) ebars and stones (no concrete) bound together within a metal grid.
A lot of the time rebar delivered to a construction site has a lime green protective paint coating on the surface of the metal. Unfortunately that’s not always the case.I often see bundles of strapped up rebar rusting off to the side of job sites.
@@loadedfun4764 yeah and as soon as it starts getting manhandled around the site and scraped and scratched it seems like a futile endeavour, I've never seen it painted myself, perhaps that's not an industry standard here in the U.K
Steel fail in an explosive way, almost instantly, while concrete "let you know" in advance by the amount of cracking. If you need to keep an eye on structural integrity by easy examination, what would you prefer?
@@PracticalEngineeringChannel With a rig already set up like this, it would be cool to demonstrate the difference between under- and over-reinforced concrete beam failure and the safety consequences of each. I had this demo a while back in my civil program and it is quite a sight.
@@jekomac you got it backwards. Steel is ductile and stretches prior to failing. Concrete is brittle which is more explosive fail. The correct amount of steel is what will "let you know" when a structure fails.
Hmm, using fibers in concrete reminds me of the old clay castles in arabia where they used straw and other plant fibres to stop their clay from cracking... Old knowledge still seems to be the best! Thanks for the video, i really like the concrete "series" and its nice to see a follow-up! EDIT: Wisdom changed to Knowledge for definitions sake. (English is not my first language)
AcolyteArathok and also did you know the word “improved” exists, it’s not that “old wisdom is the best” but that we _improved_ our ways of building once we discovered new materials
Basalt fibers are also starting to be used in concrete. They have many of the properties of the glass fibers, but they do not suffer from issues of high pH causing lack of binding or fiber damage and are more economical to produce. You can do some crazy things with a high strength mix and high levels of glass fiber reinforcement, like having bends in the final product, have high strength with light weight, and impact resistance. I am surprised that a company hasn't started making roof tiles out of the stuff since you could go thin like slate, but have immunity to hail damage. It isn't hard to get a mix for glass fiber reinforced concrete to be impermeable to water either, so you don't need the thickness that current concrete roof tiles have to keep the water out. They would also last longer than a slate roof since they would not suffer from broken slates, so we are looking at 50+ year roof life easily.
Hi Grady, I was watching your videos, well done mate, great work, it is interseting that both of the fiber reinforced concrete beams that you tested failed in Shear rather than bending (which is expected due to the beam length to depth ratio and having NO shear reinforcement) I would suggest for the next test add some minor 6mm shear reinforcement near the supports, that would make the beam to go long way before failure. Thanks for the great work you are doing
One of the largest problems with fiber reinforcement that we have yet to find a solution to is early fault detection. A giant crack is easy to notice, tiny ones, not so much. A beam can fail and still hold a load with traditional rebar reinforcements, but it doesn't appear to be possible to do that with fiber reinforcement
In literature (and practice probably), researchers are testing and using fiber optics to accurately monitor strains in concrete structural elements. That way it would be possible to see microcracks, providing the accuracy is high enough.
No mention of hot dip galvanized rebar? Still fairly cheap and much more resistant to damage than epoxy. In Bermuda we have lots of salt exposure and ungalvanized rebar is not allowed by the building code. Even the tie wire has to be galvanized.
The heat from the process dramatically reduces the strength of the rebar. When we send brackets for our elements to galvanization, it is always with normal round bars. The code for the industry (Eurocode) prohibits galvanization of rebar. I live in Denmark btw.
@@HepauDK definetly not dramatically. zinc has a very low melting point. most galvanisation processes take only a few seconds wich is barely enough to fully heat the rebar up. at least when done right of course
Behind the house I lived in, in S.E. England, when I was a teenager, there was a 2 m high wood-reinforced concrete wall. I believe it was built in the early 20th or late 19th century. I'm not sure exactly when, but it was a long time ago. The wall is still there and still sound as far as I know.
How weird. Was thinking about rebar yesterday and saw this video in my recommendations today. Thanks for answering the questions I had but did not ask.
Great video but wanted to add something regarding corrosion. Although a much slower process, rebars in reinforced concrete members not subjected to marine environments or de-icing salts can still be subjected to corrosion via carbonation of concrete. Carbonation occurs due to atmospheric CO2 uptake and subsequent formation of new minerals (such as CaCO3), which do not provide this "protection layer" anymore and destroy the protective coating of rebars. Oddly, carbonation actually is beneficial to plain concrete, increasing its compressive strength!
As far as my knowledge in chemistry reaches, the CO2 alone actually can't corrode your steel, as the corrosion process itself, needs water. Concrete is alkaline, due to the amount of Calciumhydroxide in the mixture, wich can react with acids to form a salt of Calcium and water. The most common acid, is Carbonic acid, as this one can form by CO2 diffusing into water. So yeah, it isn't that much of an issue, since fluids diffusing through solids is horribly slow, and you can protect your concrete fairly easy by keeping it dry.
if the people build homes like the old ones (made with clay, stones and hay) emulating what in the video say (reinforced concrete with glass fibers) the buildings last more and are safer
The failure in the tests shown for those beams are both shear failures because they do not have any stirrups. Although the purpose of the test was to compare the differences between the cracks at the bottom. Great video!
+Enrico Bonomi penso che sia stato ispirato a questo video proprio da questa triste storia.. e che la considerazione finale sulla mancanza di manutenzione non sia affatto a caso :(
Penso sia una coincidenza e non ci sia causalità fra il crollo e questo video, anche 2, 5, 6 mesi fa e oltre su questo canale si ' parlato di ponti, cemento, cemento armato, crolli etc, quindi è un filone di video iniziato ben prima che il ponte crollasse
I was vacationing in Greece in the early 80's. On a ferry boat leaving Piraeus, the travel guidebook said to look for an abandoned, deteriorating apartment complex along the outer edge of the harbor. *The concrete had been mixed with seawater*. It was seen as being emblematic of the corruption and crony capitalism of Greece.
Maybe the builders heard that roman concrete set harder with seawater? My own experience of shitty concrete is a little less spectacular - my parents house was built on a hillside and during a cyclone in the 1980s (Bola) half the concrete structures holding the slope together failed, resulting in about an acre of hillside slumping into downhill neighbours' properties (expensive insurance mess all around) It turned out that the builders had used illegally obtained river gravel and sand as the aggregate some 40 years previously - and it had a _very_ high silt content, weakening things considerably. One waterlogged hillside later, this was found out the hard way - and there also turned out to be a number of sites across the area which had been built built by the same cowboys and had the same problem - not good when one of the buildings was a small (3 floor) office block in large earthquake country - that building collapsed in a small magnitude 5.9 quake in 2003 that it should have easily withstood - thankfully no injuries as nobody was in or near it at the time (late evening on a Friday, holiday weekend) but that was sheer good luck.
I've not been on commercial job sites in decades but I can suggest that the craftsmanship is likely the number one problem with construction to be as per spec. I have witnessed residential construction as being very bad in following the just the minimum standards let alone doing the work in professional methods and following best practices in the trade. I have watched hundreds of concrete pours being made for decks, driveways, walkways, foundations etc. and most of the jobs rarely bother to use "dobies" to space the rebar, if it is used, 2" above a correctly prepared foundation. Most concrete work is poured right over bare soil, no sand, no quarter rock base, and finished especially with driveways and home foundations. See it all the time and folks wonder why there are big cracks vs. small cracks years later. As in this video, the one pump job that did use some dobies but not nearly enough of them had much of the rebar lying right on the yellow barrier so no concrete is getting under the rebar. BAD. Its a wonder that workers with that kind of concern for their work continue to get another job to do that again and again.
The old guys that knew the job are gone now mostly and the younger ones don't have a professional outlook. Also, the contractors are trying to come in quick, do the job, and get out. Make the most money, hire subcontractors who use illegals to cut cost and don't adequately supervise them. The house I am living in was built in 1955, enlarged with a double car garage, which required a bigger driveway. They just left part of the old one, didn't use ANY seams in the new part, so now it is cracked drastically. The front porch has rebar stain on the concrete. Just about everything was done wrong in remodel and I continue to find more mistakes. House foundation not done right either.
I worked a summer doing concrete. Those concrete spacers pretty much tell you how to install them on their packaging or material provieded in the box. Clearly the guy who I was working for did not know or just did not care as he only used a few of them if any at all. I told him that you are clearly being paid to install concrete the right way and not his way. We were doing a finished concrete foundation and floor ( mono pour ) for a pretty nice house and he did not use any of the spaceres and the guy spent a lot of time grading and preparing the site along with insulation, forms and providing the drawings for the rebar. We show up and he tells us to lay out the rebar in a 2x2 pattern and leaves for a few hours. While we did this the guy had a workers lean too that you could look at the plans and had copies of everything including the rebar foundation. I looked at all of this stuff. When the boss got back I asked if this was how it was suppose to be and he said yes. So while he was not looking I snapped a few photos and we poured the concrete and finished it. I then went to the homeowner and showed him the photos. While we were working on the next job I was offered a much better job and took it. In the end the home owner threatened to sue him and he ended up having to to rebuild the entire foundation and slab. With all new plumbing and floor heat and everything to the exact specs. I am sure it cost him double or triple of what it should have. He no longer does concrete anymore and now is the county road and bridge main supervisor. I hate that guy as he cut so many corners. He did the same on a county remote shop which was my first job. I did with him.
@@kameljoe21 Seems to me the entire system of being licensed, having just anyone on the crew plus the inspections that are supposed to be catching the cut corners isn't working. Is Everyone on the take? Greedy state and local license, permits, fees, plan checks and corrections galore to satisfy the very people who allow cheaters to cheat for a bribe of some kind. All while the owners get screwed and the public are subject to more risk factors when entering buildings and using just any kind of structure. People are so absent minded about the years and years that will pass and this kind of activity will continue to put folks and owners at risk.
@@Garth2011 Oh did I forget to mention this was in rural areas where permits are not required and inspections do not exist. Put it this way where I live I can build a brand new house with out asking anyone. The only thing I have to abide by is building on my land and at least 10 feet away from the property lines. I own almost the whole block in a small town and I could build a shanty shack here if I wanted to. I have also been thinking about doing that. Building a super small cabins for hunters and renting.
@@kameljoe21 Seems fair...if the location has no codes/rules in the building of structures then its up to the builder to research and build a safe etc. building. Problem is, that is why building codes came about, your average building didn't care about the future, safety, efficiency etc. of what they had in plan. they simply just build it any old way but that puts people in risk, property at risk and much more. So that makes it all on the builder/owner...I hate to admit it but building codes get my vote long before I'd trust a Joe rural builder.
Could you possibly do some testing on fiberglass rebar? It costs less than steel right now, but cannot be used vertically. Also if you can't find it with a minimum order of one, I can mail you smaller pieces.
what do you mean by vertically? as shear reinforcement? as far as I know, it can be used and it is actually heavily used in countries such as Canada where corrosion due to de-icing salts is a common problem.
What do you mean "cannot be used vertically"? I used to work for a place that made fibreglass rebar and one of the case studies (i.e. sales pitches) for it shows it being used vertically and horizontally with cast bends between the two.
Meanwhile, latin countries required that the iron bars need to be treated with a polymer based coating to prevent corrosion. The concrete formula needs to include hydrophobic component. Please explain Hydrophobic layers to protect from corrosion. That would be helpful. And yes..adding fiber glass fiber, metal shard and granite or other minerals can help but it about the combination of these solutions.
Taught in every university: Planned obsolescence, skimping on materials and cost cutting. Companies are in business about quality but time and savings. Thus the majority will never get a quality built building or housing unless you do it yourself.
Paul Kirkham Ohh there happens magic. It is much more amazing then that. Maybe we will see it in a video some day. I just know what happens but not why it happens. That's why I would love to see it here.
*slaps roof of reinforced concrete structure* This bad boy can take some much stress before cracking up. Here is a table with all the information you need.
I used to work for a company that manufactured industrial paints and coatings called Tnemec. Their flagship product was a coating that prevents rust. It came about because one day the founder of the company noticed some rebar sticking out of old concrete rubble and noticed it wasn’t rusted. Long story short, they made a coating with cement in it which then had the rust inhibiting properties. The name Tnemec, is cement spelled backwards. Tnemec makes all kinds of coatings for many things like zinc based coatings for water immersion service, water towers, coatings for bridge beams, sewer linings and even aerogel coatings for thermal insulating… pretty awesome stuff. The list is pretty impressive and I only named a few.
Grady, thank you for another one of your excellent videos. Your explanation of concrete/rebar failure provides context for one of the possible failure conditions for the tragic collapse of the Champlain Towers South in Surfside, FL.
First line of the video: "Concrete reinforced with steel is the foundation of our modern society". I love this guy.
TOT, you keep showing up on all of my favorite channels!
*MY* favorite channels. * shakes fist *
It is also, say, the foundation of all western thought since 1900, and it has supported nearly every artist, writer, performer, and us regular nudges since then.
(Also, glad to see TOT and his shaking fist.)
Tony ain't that bad either :D
Modernity was a mistake. That isn't a dig against steel or concrete reinforcement, it is how it is being used in housing, roads, and other infrastructure to centralize production centers and keep jobs, opportunities, and property rates localized. Commute times are getting longer and the last thing people think is what a marvel their congested roads are.
I retired from a water utility where they had installed a lot of pre-stressed concrete pipe. It looked like a really good idea in the 1960s and 1970s. It could be fabricated to some very large sizes (big enough to drive a car through).
Unfortunately, the pipe manufacturer didn't coat the rebar. Keep in mind that water infrastructure is usually installed with expected lifetimes of more than a century. Only a couple decades later, the pipe began to break. Today, the problem is very serious. It's so bad that all pipes of a certain size have fiber optic sensor cables in them. They're listening for the "pings" from breaking rebar.
A few years ago, on July 1, they detected a series of seven pings. It was a 94" water main. Crews immediately dewatered that segment and began emergency repairs to dig out that section and replace it. Water supplies were shunted to an older 48" main. We survived the July 4th holiday with the very good fortune of not having any house fires. Thankfully due to reduced demand and dumb luck, we got the repairs done before anything bad happened. We were concerned that some places in the service area might not have sufficient reserve water for fighting a large house fire if water demand was more than typical.
Later, when the pre-stressed concrete pipe that was removed from service was examined, they found seven breaks in the rebar where corrosion had compromised it. Had it been left in place and allowed to break, it could easily have washed out several buildings.
This is something we really need to get right, or there will be terrifying consequences.
Jacob Brodsky thanks for the interesting read.
7 pings for 7 breaks, that's some good sensoring!
I'm trying to imagine how much water a 94" pipe can transport. If it blow out completely, it would be like having a river flowing through the backyard.
69aussieguy That’s some complicated Math. At 100 PSI the water flow per second would be, ah, ...a lot
pre-stressed concrete doesnt 'ping' it is anchored along its length, i think you mean post tensioned?
Awsome. I couldn't agree more with your statement, "many disasters have come to due to lack of maintenance rather than lack of design..". As a person in the maintenance field, i can appreciate that statement.
Hey Stars, how long does it take concrete to erode and be dangerous. We have a concrete beam and it has been exposed to rain for 12 years with some rust on the rebars. Is it dangerous?
On the next vid he should test covintec that stuff is grate it has lots of steel and it can resist tons and tons of load
This video could not been more important than today with building collapse in Surfside Florida. Look no further than this video. Thanks.
Yep. That’s why I’m here.
Why do you think this video was reuploaded so many years later?…$$$$
well look at google streetview and map. They have been building a new structure next to it much closer then the original building they demolished. So it is possible the concrecte got damaged because of the new work done there. It happened before.
@@klaasj7808 That’s unlikely. The latest reports suggest that the culprit was poor maintenance over many years, which allowed prolonged flooding of the basement, which most likely caused the same sort of corrosion described in this video.
@@MarcosElMalo2 maybe both, when it was already poor and new building arises accomplished with heavy machinery then this whole process went even faster. dont say they did anything wrong next door, as they couldnt know.
Love the fact that the narrative is talking about cover @ 2:41 and the screen shows the rebar on the ground with hardly any standoffs.
I have seen concrete placed in these conditions. During the concrete placement the contractor will have a crew member with a hooked piece of rebar. The hook is used to lift the rebar as the concrete is placed and then consolidated with a mechanical vibrator. On a side note, the yellow Stego Wrap (15mil) vapor barrier is another technology used to help protect the concrete from the corrosive soil and gas in which it is built upon.
There is no point at putting the rebar where the concrete will compress. And if you are pouring a slab for a house or garage it should have a vapor barrier under it.
Exactly. Rebar makes a very poor vapor barrier.
Rebar without the designed cover doesn't perform its intended function in addition to being prone to corrosion.
@@nosadonions3231lifting with a hook or a rake is not the same as implementing correct cover with chairs.
I've noticed that many American concrete placing professionals don't really understand the purpose of rebar. It's not just reinforcement it's tensile load bearing. Each bar has an optimal position in the concrete element.
One of the reason the process you mentioned is avoided in Civil Engineering is because the proposed system give less visual cue before failure happen. The new concrete mixture you mentioned failed at around the same load level as regular reinforced concrete, but it doesn’t reform like regular reinforced concrete. This make it difficult for inspector and give little warning before in failed. One of the lesson I learn at our concrete course is that’s don’t over-reinforced concrete, which can create sudden failure. We want to design it a way that before concrete failed, it give enough visual warning so inspector or normal people can catch it and evacuate. The new mixture give less visual warning to inspector. It might prolong the life span of product but it might create more dangerous condition if doesn’t use it accordingly.
The first enemy of reinforced concrete is moisture and water coupled with the subzero temps during winter. When water makes its way in minor cracks it reaches the rebars starting the oxidation process.frozen water expands cracking and literally destroying the cover concrete exposing parts of rebars. Here in Italy in front shore building we use hot galvanized rebars, coupled with additives on the concrete making it water proof. A galvanized rebar is basically eternal . Obviously costs skyrocket since the rebars are sent to the galvanizing facility .
The problem here is a shear failure for all three beams without shear reinforcements, so it breaks suddenly as it is a fragile response. In fact fiber reinforced concrete does show very large cracks before failure but not at the service state, so you know that when fissures can be seen in this type of concrete you can assume that a failure is at risk.
If the use case was a single family house single story foundation. I wonder if Would failed here be less catastrophic and benefits of longevity more valuable?
@@3dvorator come see Canadian highway bridges where salt is used heavily in the winter. I can assure you hot dipped galv rebar is far from eternal. 10-20 years maybe before you start getting higher maintenance required
@@coadycarter9230 we use galvanized brackets on floating dock ( which floating tanks are actually reinforced concrete built ) and they stay submerged in salt water decades. 🤷♂️🤷♂️👍👍
At London Heathrow airport we had a serious strength problem with the concrete being laid for the then new Terminal 5.
A new concrete mix was being used that was much stronger than previous formulas. It could be laid faster and thinner with significant savings in time and cost. It was a good candidate to be used for any new apron/runway works elsewhere at the airport in the future.
Specimen slabs were taken from every pour, and tested at 1 month, 2 month and 3 month intervals. Then, many months into the project, and with less than year to opening, specimens started to fail the strength test. It was very puzzling as the constituents seemed to be identical those in the specimens that passed. This was a major concern as it could be very costly, especially if more concrete had to be ripped-up and re-laid.
The detective work turned-up a surprising result:
One of the ingredients was fly-ash from coal-fired power stations. It just came in on a contract from the power company. The main source power station had been shut-down for summer maintenance and the source switched to alternative power station without our knowledge. The fly-ash was chemically identical but it was ground more finely - and the more finely ground fly-ash absorbed more water, and concrete made from this wasn't as strong!
Once this was discovered the problem was quickly resolved and concrete strength restored for subsequent pours.
And Terminal 5 is one of the finest airport terminals I know, and one of the most interesting projects I've worked on.
(My involvement was in managing overall project risk and, as a physicist, had no connection with the concrete laying activities.)
Never use fly ash its full of dangerous elements some even radioactive - better to use a mined and milled Pozzolanic material.
Fly ash is shit half the time. I prefer mixes with Furnace slag instead.
That was fucking FASCINATING. Thank you for sharing!
Fly ash is indeed toxic waste left over from dirty coal power.
Gavin ward They should have discovered at some point,that they needed more water to make the concrete ! ,
I'm watching this video one week after the condo collapse in Miami Florida. Can't help thinking how important the message is in this video.
Wrong question. Steel does indeed rust. Steel used for reinforcing concrete MUST BE COATED TO PROTECT AGAINST RUST. Concrete is ALWAYS WET enough to cause rust of any steel that contacts it. Most contractors go through life lying, stealing and cheating - they must be republicans. Corruption in the building industry is a way of life for... oh you get the point.
@@thatguy-art6229 Way to bring politics into a non political situation.
@@Tanmay.Patil1 Yeah as much as I am for pointing at a political party opposite of my own, this is one of those instances where I can't pin politics on it in anyway shape or form, despite the ways we can point in that direction. This one is really between the owners/managers of the property and possibly the contractors. I'd leave the conclusions up to the investigators.
@@Tanmay.Patil1 Maximizing profit over saving lives goes hand in hand with conservatism. Conservatism is absolutely the reason there is inadequate regulation overseeing building maintenance that would have saved those 100 people.
The conservative mindset- individualism, the aversion of regulation, taxes, HOA fees, and a lack of care for the public- is directly what got those people killed. Check what Ron Desantis has said about the collapse. It is absolutely a political issue.
Every time you post a video I gain a new found respect for the civil engineering all around me, that I use every day and hardly notice. Thank you.
Good stuff. I'm not an engineer, but I have been involved in the construction trades for my entire working life. I enjoy your vids because the are informational, technical, factual. There is so much anecdotal evidence and misinformation to deal with in the trades.
In this instance, concrete legends and lore. I hate hearing "Add five gallons". "Add ten gallons." Right, slop it up to make it easier to place, wait longer for it to set, break it out when the test cylinders tell the truth. Grrrrr.
Before a pour, I go to the concrete supplier, meet with their engineer, discuss our expected result and our site conditions and their recommendations.
"Oh! They're trying to jack up the price per yard!" B.S. They aren't dummies. Their continued success depends on satisfied customers and word-of-mouth.
They know much more about concrete than I do. I'm going with their recommendations.
Side note...
We were pouring a slab 36" deep. 100'x25'. The crew and I formed it up, installed rebar, etc. We scheduled it for the following Monday. Over the weekend, the weather forecast called for -0 degree temperatures Monday night and into Tuesday.
We tented the area, heated it, and went ahead with the pour and then insulated it. The engineer for the concrete supplier came out Monday morning and stayed on site until the pour was complete and insulated. He even brought out several pairs of Ninja cold weather waterproof gloves. What a heck of a good guy.
Work with and trust the engineers.
The last line is imperative to good construction work. If you're petty and too stubborn to work with someone that might know a bit more about something than you that's when problems start.
I just found this channel a few days ago when it popped up in my suggestions on YT. I've been a bridge inspector for over 20 years, so little of the concrete series is new to me, but still very interesting and I've surely learned a couple things I'm currently on a major new bridge construction project with a staff that has not had much bridge experience. I am certainly going to recommend that all of my staff subscribe to the channel.
I began my career as a surveyor in a small surveying/CE firm in the mid 70s. Before too long, I was in the office, designing subdivision roads, open channels, culverts, sanitary sewer collection systems, etc.... all of this without benefit of education beyond high school. Your Civil videos add background to the things that I understood only logically those many years ago.
To any viewers of this channel that find this stuff interesting, I can only add that... "I wish I'd paid more attention in my math classes!"
I like that you reinforce your videos with concrete data. Even if the measurement system is a bit rusty.
As a LEO, I have no background in civil engineering or whatsoever, but somehow after watching almost all of your videos i know pretty much the basic of how some things work. Thanks for sharing your knowledge with me dude, hope your channels keeps growing bigger than ever before!
Why do we use steel? It has a thermal coefficient of expansion almost exactly the same as concrete. This has been called "the single physical fact that contributes most to modern architecture".
As a Union Concrete Journeyman this is one of the best video collections.
Exactly that's God's gift.
We use steel if you want to consider dead loads as a critical function in design (as a steel beam is almost always lighter than a concrete (even prestressed) girder - for the same design capacity). You might also consider steel if a primary load carrying member is curved. Otherwise, PS concrete and reinforced concrete is an efficient design approach.
While the thermal coefficients are similar, both materials don't necessarily adapt to temperature changes at the same rate. The physical fact that chiefly contributes to concrete and steel working in a compatible manner actually seems to be the adherence between them. And definitely one of the greatest contributions to modern architecture, of course.
Because steel was ductile
So basically hummanity went from making mud and straw structures to fiber reinforced concrete. Same concept, higher tech.
Hahaha, I was coming down to the comments to say pretty much the same thing as soon as I saw the fibre reinforced concrete! XD
Plaster and horse hair is another old one. The ceiling of my old bedroom had almost an inch of that on wooden slats before it all came down
Exactly what I was thinking, this reminds me of Cobb construction.
Cobbcrete (TM)
@Kiritsu - Actually some of the oldest man made structures are made from granite and basalt stone.
Examples: The Pyramids, the megalithic walls of Peru, and so many others around the world.
These structures have endured for many thousands of years.
Who made them? How where they constructed? No one knows. :)
@Kiritsu: I had a similar thought when I saw the fiber-reinforced concrete being poured into forms. :)
Interesting that Google is recommending this to me today:
The experts are saying that 'Salt Oxidation, via Concrete, of Rebar' was likely involved in the Surfside Miami building collapse.
I live in Florida and you see a lot of old condos from the 50s, 60s, and 70s along the beach. I often wonder how long the rebar in the floors can withstand the salty air. There is one in Cocoa Beach where the floor is visibly sagging above the carports.
I came here looking to see if anyone made this comment.
Exactly why I'm here too.
Me too… this is what I figured. Have you seen cars that live in salty air areas? Bad news
@@CASANOVAPRO1985 yes I love in nova Scotia some concrete right on the water will get really brittle get big crack some you can break off with your hands
Dad was a rodbuster and I spent many a summer working for his company packing and tying steel. It is likely that humble background that caused me to get my engineering degree and complete a 30 year career in the business.
There was an interesting case in Soviet Russia with Luzhniki Metro Bridge in Moscow. It's a double-decked concrete arch bridge and It was built in the late 1950-s and in record times, about 19 months. To speed up the construction and to be able to continue pouring concrete during the Moscow winter they used salt in the mix to make sure concrete can properly cure at -10C/14F. The bridge rapidly deteriorated and had to be partially closed down only 14 years later.
Fascinating. Meanwhile the Romans created concrete that has lasted for 2000 years. I don't understand why we can't crack their code.
@@FablestoneSeries Practical Engineering has a video on that exact topic of why Roman concrete is not better than what we have today. First, there is no good reason to spend the time and money (taxpayer dollars) to build something that lasts thousands of years when it really only needs to last a few decades before it is torn down for something better or to meet new demands of being built somewhere else. There is no reason to build a road or bridge that lasts 1000+ years when cities are created or are abandoned over the centuries, when routes need to be changed to meet different traffic demands, when bridges/roads need to be torn down or rebuilt for environmental reasons, and even rivers change their patterns every few centuries. So those surviving Roman structures are overengineered and impractical in terms of cost-effectiveness and are not flexibile enough to meet changing needs.
Second, outside of PE's discussions, there is survivorship bias where only the best built Roman buildings (their best civil engineering projects) survive to this day while the vast majority of average or lower quality Roman buildings have crumbled/disappeared. For example, you typically don't see any Roman apartments or regular Roman house from the Roman era survive to this day even though they were the most common type of building.
Third, Roman buildings such as the Roman Pantheon were actually in continuous use through the middle ages, so they were continuously maintained and repaired.
@jeff mattson Practical Engineering has a video on that exact topic of why Roman concrete is not better than what we have today. First, there is no good reason to spend the time and money (taxpayer dollars) to build something that lasts thousands of years when it really only needs to last a few decades before it is torn down for something better or to meet new demands of being built somewhere else. There is no reason to build a road or bridge that lasts 1000+ years when cities are created or are abandoned over the centuries, when routes need to be changed to meet different traffic demands, when bridges/roads need to be torn down or rebuilt for environmental reasons, and even rivers change their patterns every few centuries. So those surviving Roman structures are overengineered and impractical in terms of cost-effectiveness and are not flexibile enough to meet changing needs.
Second, outside of PE's discussions, there is survivorship bias where only the best built Roman buildings (their best civil engineering projects) survive to this day while the vast majority of average or lower quality Roman buildings have crumbled/disappeared. For example, you typically don't see any Roman apartments or regular Roman house from the Roman era survive to this day even though they were the most common type of building.
Third, Roman buildings such as the Roman Pantheon were actually in continuous use through the middle ages, so they were continuously maintained and repaired.
I'm experience, not an expert. with that said, no wonder it failed. The temperature alone will cause it to fail. The salt didn't help the curing process, it only hurt it and made it cure weaker. Salt won't make the cement get warm enough at that temperature, calcium chloride will but even then it will still cause corrosion and can make it weaker.
@@Intranetusa I'm seeing a debate by me about replacing a bridge that is 100 years old. There is so much debate about it that the only way it's likely to get replaced in any sort of hurry is if it actually breaks and causes a major traffic disaster in the process. I would say that's a great argument for building a bridge that could last a thousand years. People refuse and wait to change things because they're stupid.
Might be time to revisit this topic, sir.
An official of Surfside, Miami stated, “We are all scratching our heads asking how this happened? “ We know how it happened. We have the science..its explained here pretty clearly. Bad design, building and maintenance.
@@EricDMMiller I heard they were using epoxy for patch up jobs. 🤦🏿♂️
@@romeysiamese6662 I saw a reply on another vid: Them: How did this happen? Me: How did it NOT happen?
@@EricDMMiller Harsh words. Harsh... but true (minus the good riddance part).
Clearly, they did not have a clear understanding of what they were (not) doing. That is not the engineer's fault - records clearly show that he strongly advised immediate remedies in 2018 - but it does shine a light on important part of human psychology. They must have read the words, but they didn't take them to heart. "It will be fine. Surely it can't be _that_ bad. This can't be happening to _us."_
Similar disasters elsewhere has seen off-site owners vilified as uncaring or even speculating in the collapse of a building. That might sometimes be the case, but even the most callous of developers will realize the trouble they're in when I building they are responsible falls down and people die. I think a far more likely explanation would be same kind of magical thinking displayed by the people living in this complex.
So that leaves us with the question: what facts am _I_ ignoring based on wishful thinking and internal appeals to incredulity?
I'm a Building/Structural Inspector and this has given me deeper look/understanding into Structural builds. Thank you.
If that's your job, I'm concerned that you didn't already know this.
Hey Grady, Thanks for putting together these videos! You have a way of explaining things in a straight forward manner, without the "I'm better than you" attitude that most engineers seem to learn in college.
The intro "Hey I'm Grady..." and you know you are in for a learning session.. Well presented and all the tech info is clearly explained and demonstrated. I am a gas engineer and love Grady's practical engineering channel. Its taught me many aspects of other engineering fields. Great channel, thank you Grady for your hard work and enthusiasm.
I would never have believed that I could sit through successive videos on civil engineering and be fascinated throughout, yet, here I am again, having watched yet another clear and engaging video. Good on you, Grady! 👍👍👍👍
This might come as a surprise to alot of persons. If you pour concrete over slightly rusted steel members, the abrasion between the mix and the rebars actually removes most of the rusting in the surface of the rebar. Discovered this some years ago while doing a demolition on a floor slab I casted years prior, the rebars actually appeared brand new out of the factory.
was this before the chinese steel invasion or how many years ago did you buy that rebar.
@@brianblithe2271 doesn't matter.
does matter because the rebar today is so bad you cant even epoxy it, it will still rust@@ItachiUchiha-ff5yb
@@brianblithe2271 its made of the same mild steel thats always been used, please be quiet
@@mhxxd4 BS.
"If you prefer SI, just pretend these are metric tonnes." LOL. Love it.
I always found it weird the Metric System would have a unit that's pronounced the same as a similar Imperial unit. Why not "megagram"? Mega is a viable prefix and grams measure the same thing (mass).
@@foxymetroid Um, I don't know if you're joking or you're playing a smart ass... but Tonne actually IS correctly called a Megagram. That's the official name. If it was just a lucky guess on your part, well, you're right! :)
@@foxymetroid Ton/Tonne isn't originally imperial or metric. The name comes from an old measurement of volume called tun, basically a standard-ish wine cask, eventually turned to general expression of something being very heavy (I.e. "it weighs [like] a tun"), turned to sort of a unit of measurement. The full cask would weigh about 950kg or a wee bit more than the 2000 pounds of a US ton. Basically, it was a parallel development with people being people and just kept using the word, made it more precise to get on with the times by merely rounding it down/up to a nice number that made sense in the system they used.
@@stevendeamon I didn’t know that. From now on, I’m going to say megagram.
I prefer unit Newton for forces.
I constructed and maintained bridges for the state of SC for 34 years. Although some of the bridge beams we used were not of the best quality due to poor quality control at the beam plant, most of our problems came from lack of maintenance, When I would make complaints to management, I would get answers from the SCDOT top manager that the public did not see the underside of the bridge. What he was trying to say was the money for proper maintenance was not there and we would have to do our best with what money we had. I would get really pissed knowing that I was spinning my wheels trying to keep the bridges in my district from falling. Some are really in bad shape and only get money for repairs when the inspectors rate them critically. Not only were some of my bridges state-owned but interstate owned by the Federal Government. Many of the major repairs I did were bridge bearings due to lack of maintenance. Many with stress cracks from bearing failures. I could go on with problems I tried to repair but money is a key issue. It is expensive to make repairs to bridges but the flowers alongside the road look much better for those in authority.
Sir, who creates the money problem ? The govt. authorities or the private company for which you were working. Why would be there shortage of funds from govt. side as it's all public money and US govt. has most money on planet.
Suraj Tomar that’s not how it works.
As said by a US Senator: infrastructure is boring. Also, the attention they get from maintaining infrastructures is not as much as creating new ones, so there is that.
@@SurajSinghTomarArya The "Free Lunch Anti-Tax Republican Party." They don't want to pay a single tax, but still want America to be the best, baddess, and meanness Country on earth, ... for free.
Raymond Myers uh no. In SC they just put through doubling registration fees for vehicles, license fees and taxes in new vehicles to “fix the roads”. The only roads being fixed are interstates. Secondary roads?😂😂 I do hope if you visit SC (where I’ve lived all my life) you did pay a little extra for the struts with coil springs on your car or truck. We’ve just gone through the wettest winter on record and the potholes are abundant. The only good thing about them is it does slow traffic on our road which usually is flying (two lane road) shoulder in some places, others ??
We already were paying some very high vehicle taxes before the incremental doubling went into effect. The money is going somewhere but not into asphalt on secondary roads. The interstates will be masterpieces but getting to them will kill your vehicle.
A road near us was “resurfaced” recently-sprayed with tar and pea gravel spread on top and a ditch reshaped on one side near an intersection. I have seen four cars, two pickups, and one tractor trailer stuck in the ditch because if you swing wide to make the turn, the new ditch starts at the edge of the asphalt. Zero shoulder. None. When I say stuck in the ditch I mean the cars passenger doors were on the bottom of the ditch and the people driving had to stand on their consoles to open the drivers door nearly straight up to get out.
Who in their right mind signs off on these projects when complete?
you know i never saw myself doing engineering until quite recently in my life, it's so much more interesting than I thought! I'm really glad there's channels like yours
If you came here after the surfside collapse.... thank you for wanting to understand and learn! The world needs more people like you, in order to grow as a whole.
Brilliant, thank you. My 2 brothers and I were raised on a diet of all things concrete as teenagers. My poor late father purchased a manual block maker and we spent 2 summer holidays making our own 6in concrete blocks using semi dry concrete that we mixed ourselves. Approx 20 blocks a day, not for the faint hearted. We thought we were great, what a great experience, thanks to our Dad. We have since seen lots of rebar used on other jobs round the farm, and my concern has always been when will that rebar rust!!! I really enjoyed your video, thank you again, my youngest twin boys now 16, are keen to follow up some form of engineering at university hopefully. looking forward to more videos.
I my dad was a cement finisher all his life, I can relate
A Carragher, good familie experience on your farm. But make a block ist a simple think, make a concrete roof is an other think, tha is the problem. Dont make your own roof with concrete, without a good advice(Spezialist). realy no es very complicated, but the details are important. No es nesessery go to HIGHSCOOL fore that Job, ist nessessery open your eys and ears and understand what means work like a man in the field.
A man can do everthink, today take a laptop and google around, make some experiments on your farm, and go on. Concrete is a beautifull Material, cheap, but
need a strong man , to dominate the Concretemix, like a devil. Ever low water, the rest go hard ike a stone alone (28 days), and the construktion is your own. Go ahead, young Boy, the time is running away, and nothing is done. When you make fenceposts , dont put steel inside, the steel will brake the post, better more thick the post, little bit more concrete, better result.
The Concret devil
i
Very cool demo - Next: Small scale pre-stressed rebar?
he did it in another video
Dang! Missed that one, thanks.
3:30 "he did it in another video" but he stated it was only briefly and would like go into more detail into in subsequent post. BTW some of the things he say is miss leading...
And y Dang! it not cool to look at past posted vids? lol
No, he did post-stressed rebar with a threaded bolt. He hasn't done pre-stressed yet.
Incorrect, he states in this vid it was "pre-stressed" not post-stressed rebar...And if the rebar is freefloating the issue of it being pre-stressed vs post-stressed is a mute issue.....
May I request a topic? :) About concrete pouring under water? :)
Yes please
Potchi Boy yes do this please! Or just bridge building in general
Hi Potchi!
Concrete does not actually dry like a wet towel, by evaporation, to become strong. The water molecules reacts with the cement in a process called hydration. So the water actually stays inside the concrete forever, and therefore, concrete may also set underwater. A more common problem is that the concrete is evaporating water in hot conditions, making the finished product have a rough or cracked surface, and that is why newly poured concrete is sometimes sprinkled with water. I am not a chemist and haven't thoroughly read up on the subject but I hope I was of some help.
Nothing special for "pour" concrete underwater.
You need form where it will be pumped and pumping will start from bottom and keep hose there until form is filled concrete pushes water away when form fills and that way only top part of concrete touches water and rest remain pristine.
That top part is sacrificial layer and isn't include part of designed structure meaning if you need 10"x 10" and 3 feet high footing example for pier form needs to be like 1 foot taller because that top layer becomes weaker by touching water.
Treme method is used google it
You started a circle and closed the loop! Excellent from problems, cause and solutions....Bravo. now go change the world!!
One of the reasons why you don't very often see stainless steel rebar (or other alternatives) in concrete is because some of the most common stainless steel alloys have a wildly different thermal expansion ratio. Meaning that if your reinforced concrete cools down or heats up, the 2 materials will expand at different ratio's which causes cracks of its own and a range of other issues. Concrete and good old steel are pretty closely matched however, meaning that cracking due to thermal changes is pretty much a non-issue.
The alleged corrosion resistance of stainless steel is dependent on exposure to oxygen, which causes stainless to form an oxide surface that protects against rust.
I was missing this aswell.
The range of properties for SS is due to the fact that "stainless steel" is not a well defined term. There are a variety of approaches to getting steel not to rust and these are all generically called stainless steel though they have very different physical properties, based upon which other elements are added. ASTM does create(validate) various standards but the real reason why stainless hasn't caught on is cost, strength, and most importantly !!!!BY FAR!!!!! is ductility. Good old fashion steel will stretch but not break, the perfect building material. Adding more carbon, nickel or chromium might increase some desirable properties but it also makes the steel more brittle. The worst property possible when parring to concrete.
Meaningless overprice.
I love this channel and the way you explain civil engineering concepts is excellent. Our society is abundant with engineering marvels, it just needed someone like you to explain it to the common man for them to appreciate it's value. Thanks a lot!
I've said it before and I'll say it again: this is an outstanding channel!
This video is an excellent basic teaching of concrete and steel rebar.
2 weeks ago ( June 2021)
A massive 12 story Condo in Florida located close to the ocean collapsed.
It's easy to see NOW how salt water can corrode the rebar and cause deterioration.
It's a sad fact of our industry that an engineer talking about concrete cover can't find stock footage of a slab being placed with the reinforcing properly supported on chairs.
The Essential Craftsman channel has some good videos of proper concrete reinforcement and form set up. He walks you through the process on doing a few different projects, including a heavy retaining wall for site prep for building a house. It is a great channel for learning about the construction trade.
He is also completely insane with his skillsaw skills. I am talking ripping a 2x4 to have a 45 degree bezel on the edge freehand type skills. Serious DO NOT TRY sort of stuff.
Well it served as a nice counterexample ;)
That's because in the real world chairs are hardly ever used.
If you need the slab or wall to really hold up, you do need a method for holding the rebar in place until the concrete cures.
I do inspections on slab reinforcing all the time. They never use chairs. Just concrete bricks.
My experience in the building trade for more than 50 years when I have seen concrete breaking away from a building it was because the rebar was too close to the face of the finished concrete.
should I just stay away from those buildings
@@pleasedontwatchthese9593 yeah probably and call the emergency services
Clear cover
It should have minimum 40mm clear cover
@@MANPREETSINGH-wd7if minimum cover varies job to job, there isnt a set standard that it HAS to be
A very interesting topic, thanks for posting. I watched because in 2021 I had this exact problem. My 123 year old building has a roof made of reinforced concrete that was poured in place. The total thickness of the roof is only about 3 inches, so there is no cover. A section of the roof collapsed. Thankfully, no one was seriously injured. A roofer was on top at the time, and fell about 20 feet, but bounced of several pips and pieces of equipment on the way down, and only had burns and bumps and bruises. The entire roof will be taken off in the spring, and replaced with steel deck.
Impressive, given the fact that the first commercial uses of reinforced concrete were only made in the 1870s! So your reinforced concrete roof from 1898 was actually a museum piece, you were lucky that it didn‘t end up on any list of protected monuments, that would have sucked as far as renovation constraints go.
@@arrzfr sorry, math error, there, 113 years old. It was built in 1908. So far, no one has indicated it as a protected monument.
The hell are you doing living in a century old building? Buy a new 🏠
@@armincal9834 It's a business, and it's a beautiful old building. There are postcards of it floating around, one from 1926, and another from the 1950s, so maybe it should be considered a historical building.
Grady, you hit the nail on the head with the last 30 seconds. If agencies do not program the proper maintenance money, all the innovations are for nothing. We use HRP in concrete in concert with the FRP and CFR/Glass all that will do is to delay the cracking. This assumes the mixing, placing and curing is done per ACI and local specifications. Great thumbnail sketch of the problem. Keep it up.
I know of a garage that had a concrete floor poured with steel fibers mixed in. Worst thing they could have ever done. As mechanics, they need to lay on the floor to get under cars and such. As the concrete wore away from constant traffic, the steel fibers began to poke though the surface and would constantly catch on their overalls and poke them in the back. Not fun.
Their concrete is wearing away?
Why?
They probably could coat the floor with some hard durable polimer.
Unfortunate, but the concrete isn't entirely a mistake here. A surface coating of epoxy, enamel, or some other hard material could easily salvage that floor and ensure it lasts many years to come.
They make epoxy surfaces to coat garages. They are meant to stand up to the oil/etc too, so it's a good option.
They make concrete sanders. I would just run one of those over the floor. But seriously concrete shouldn't be wearing away just from rubber contact. Sounds like a bad concrete installer all around
Every beam was destroyed by the shear stress, near the support. You have another good topic to discuss: Shear reinforcement
This video is newly relevant. Looking forward to your Surfside Condo video in the future.
Yeah it starts server it up on the home page, chilling.
I enjoy the education on these topics. I would like to see a video on process to repairing bad corrosion and what to use to correct the concrete.
Thank you Grady, your work and enthusiasm for engineering continues to impress. I hope everyone out there is inspired to find a job they love (and allows them to play with awesome toys.... er, serious testing equipment for the sake of science)!
I've loved fiber mesh since I learned about it 30 years ago working at a concrete company. Problem is most suppliers don't encourage it. Often they say it doesn't really add any strength. I've explained it's about cracking, not strength. But the added couple bucks per yard just stops most people from using it.
Fiber in general, works in concrete very well and it's a cheap solution.
Fibre has a remarkable effect in stiffening up the concrete mix (you can see in the video how stiff it gets). This makes placing the concrete much more difficult, in particular ensuring that the concrete flows all around the reinforcing without leaving voids. Which in turn means that much more labour and care are required in construction. No such thing as a free lunch.
@@cr10001excellent point and perspective- loving the dialogue here in concrete- so much smoke and mirrors and shibboleths in the industry.
@@cr10001just use a plasticizer
This video perpetrates an old wive's tale and reminds me of when I attended a civil engineering unit at university 40 years ago. Part of the unit was conducted in the civil engineering lab by a crusty old technician. He began the session by asking us which is stronger in tension - steel or concrete? Many chaps answered "steel" I don't remember any students picking concrete. The tech/lecturer sort of nodded slightly and then asked which is stronger in compression - steel or concrete? Chaps answered "concrete". He then sort of smirked.
He then proceeded to demonstrate the strength of various concrete cylinders, about 250 mm long and 200 mm diameter, which we students had made the previous fortnight using various mixing methods. He put each one in turn in the hydraulic press and wound up the load until each concrete cylinder cracked and failed. They all failed well below the capability of the press.
After discussing that care in mixing made a big difference in strength as shown by the test, he repeated his first questions: Which is stronger in tension - steel or concrete? In compression? The same students gave the same answers.
I was looking at the hydraulic press, and realised that its jaws were made of steel. So I said "Steel is much the stronger, in tension AND compression". The tech/lecturer thereupon said "We've broken the record. Only one student this year can think. Usually I get 2 or 3."
[Compressive strength of mild steel is around 580 MPa. Concrete is 20 to 40 MPa]
Why do we use concrete? Because it's real real cheap compared to steel and just about anything else, and it's rigid. Folk don't want wobbly buildings. Why steel reinforced concrete? Because when overloaded or not properly made, it cracks, warning you, doesn't fail catastrophically without warning, and is fireproof. Concrete by itself fails catastrophically without any warning. In the 1920's and 1930's a lot of city buildings were built with steel frames. When they caught fire, the red hot steel lost strength and the buildings came down, usually upon next door. Concrete is a good thermal insulator - if a steel reinforced concrete building catches fire, the fire brigade usually has time to turn up and get control before it collapses. City fire brigades don't actually care much if a building is ruined by fire. But its a nightmare for them if the fire spreads to adjacent buildings and then more buildings. That's why regulations and conventions make buildings not so much resistant to catching fire, but resistant to collapsing.
I was doing garage floor crack fixing and found this channel. This is fun to watch and learned a lot
I love your videos, Grady. I'm starting to notice things in my environment that I previously never paid attention too.
Steve P I can no longer go on road trips without noticing the the beautiful and large amount of engineering involved In Overpasses and even inclined terrain. Whenever I had the niece and nephews in the car in the past we would talk about all sorts of Science and technology topics, now after following the channel for quite some time I can now incorporate some engineering. Now I just have to find a way to make math a little more fun and enjoyable for them!
notice things in the environment? i noticed someone picking their nose today while they were at the salad bar
Blox117 that's social engineering, they didn't want anybody else eating all the romaine or the good toppings.
I worked at Redland Bay Golf Club, near Cleveland, Brisbane, Queensland, Australia.
During WW2, it was an American Military Base, and they laid down some concrete pads with massive twisted, flat reo bar for large generator use I believe. We ripped it up to build a new machinery shed next to the clubhouse, and there wasn't a spot of rust or corrosion otherwise on the reo bar after some 60 years.
Probably p o get my
Very interesting. Any more details on the type of rebar? Was it stainless, or coated? Thx
Was it a relatively dry climate there? Perhaps the steel used was 'pure' and not containing the impurities that recycled steel much used nowadays has.
Tying rebar and pouring cement all day will build some character that's for sure
I first learned about rebar corrosion years ago when my wife and I visited what had been for years our favorite Daytona Beach hotel. The Americano Beach Hotel. We first visited in about 1967. I think it was brand new or relatively new at that time. We went every year for ten years but then moved on as our careers developed. Years later we went back and found that they were selling time shares as they were rebuilding the structure. We knew nothing about time shares but my wife wanted me to learn more. As I looked through the new rooms being reconstructed the first thing I saw was the construction taking place and the corrosive problem with the rebar and deteriorating concrete. I remember one guy actually pointing to a piece of deteriorated floor concrete and rebar and telling me about it. People I talked with said the repairs were not sufficient and wouldn't last. We never went back. I subsequently learned that the hotel was hit by a hurricane and is(or was) no longer habitable. When I saw the damage done in Miami, my very first thought was corrosive rebar and damaged concrete. My guess is this property is only one of many in Miami with a problem. I've seen properties built and rebuilt there without much control. Miami will cost billions of dollars to be rebuilt. Many of those retirees will loose everything they have. Government officials will most likely walk away unscathed but some are responsible for this fiasco."Due diligence".
Local government officials come and go. Often when someone new gets elected they replace staff. That is why you need Federal and State Standards/Mandates that local towns needs to abide by, otherwise you will see this continue to happen. But even then there are thousands of zoning laws that on the books that aren't enforced (until a property is sold and needs to be inspected).
Steel reo also adds ductility to a structure. Ductility allows us to design predictable load paths as well as reducing the risk of sudden failure. Additionally Steel has a nice predictable elastic deformation until yield allowing it to recover its initial shape after a load is removed.
Finally another tactic to reduce corrosion is to limit crack widths. Small cracks, often as a result of thermal shrinkage can self heal because any water that infiltrates them tends to activate the calcium in the concrete matrix sealing the crack. As the cracks get larger the effect of this property drops off.
Amazing how relevant this is today with the recent apartment building collapse in Florida
I’m in concrete repair/restoration. The fiber and steel additives are mostly used in shotcrete and gunnite applications. You should also look into cathodic protection systems, we implement these to almost completely negate corrosion in some cases. There are many different systems and it’s very interesting.
Basanite
Very interesting- to clarify, you don’t feel there is really an indication for these in most residential situations?
@@johnwhite2576I pour mostly residential foundations and see fiber in the mix sometimes
Please give us wisdom. What about PPC? Or simply not putting steel wherever possible (Foundations)
This explains the issue I'm having on my 9 year old driveway. The expansion joints have rotted out and, upon taking the wood out, I've discovered rebar run through them and frequent cracks in the concrete where this rebar goes through the expansion joint wood. The rebar has rusted inside the damp/rotted wood, expanded and cracked the concrete at the edge of the expansion joint.
5:02 that's actually a very neat shear fail, not a failure in bending.
Yes you can tell because of the 45 degree angle crack which is shear failure. He should've pressed in with the machine on the direct center of the beam where the positive moment is highest is he wanted to test the tensile strength better imo
Done that text with a similar set up in college with a non reinforced beam which is the accurate test for shear on non reinforced... haven't tested reinforced yet tho so that's my 2 cents
That beam is too short and to high to fail of bending, and the reebar is to strong. He should have done a downsizeing to get normal results
and there are no stirrups, so it was most likely to fail from shear before bending moment
When i was helping with research work at my university, one of the research projects being worked on was the use of a steel mesh reinforced polymer wrap to be used on columns as a replacement for rebar or for repairing existing ones. it removes the necessity of form work and is great for marine or highly corrosive environments. (the research project i got involved with was the use of steel fiber reinforced UHPC for steel bridge girder repair.) i was shocked to learn how much time and experimental effort goes into proving and implementing new tech and methods in the construction industry,
“Durability is as important to public safety as other design criteria.” How true. The trick is to try to convince industries of this at a time when profit margins are everything.
Also, when bids go to the lowest tender, they often won't be built to the same specs as the other tenders.
People complain about profit margins, but its the only reason all economies even work in the first place. The system has to produce more value than it consumes in order to justify its existence. All companies in said economy have to have a revenue stream greater than their cost stream or they eventually run out of resources to operate. If all companies in an industry (or all industries in a society) have less revenue coming in than going out, the whole system turns into the Soviet Union and collapses.
As economist Thomas Sowell pointed out, "There are no magic solutions. Only trade-offs." You want the highest quality stuff? That is going to cost you a lot more than a product which has its quality balanced against its cost.
The disaster that was Chernobyl in the Soviet Union was caused by the same drive for lower-costs that you see in other economic systems (they chose graphite tipped control rods instead of the West-standard boron control rods because graphite is cheaper), and they had to have the cheapest costs possible thanks to systemic dysfunction caused by lower worker productivity, due to workers not working harder to get more income, as you would get the same pay in an egalitarian communist system regardless of the quantity and quality of work you did. This lead directly to a regressive feedback loop of workers productivity dropping as they saw no reason to work for more than the minimum to get the same pay, and since the cost of not working was spread out over all workers, a slowly growing pool of workers dropped down to doing the bare minimum they could get away with without being shot by overseers/guards or shipped off to force labor camps.
Unlike private companies which can be sued for bad practices in the West, the Soviet government (which owned everything) didn't have to care about safety standards because Soviet citizens couldn't sue them for disasters caused by them.
@@GreyWolfLeaderTW, you mean this Thomas Sowell? “Electric cars may be fun at amusement parks, where they don’t have to go very far or very fast. But if the consuming public wanted electric cars for regular use, Detroit would be manufacturing them by the millions. Only people infatuated with their own wonderful specialness would think that their job is to coerce both the manufacturers and the consuming public into something that neither of them wants.” I have always found his views simplistic and informed by a far right ideology. The passage I’ve provided is evidence of this tendency. The data on advancements in electric car technology prove his views to be incorrect. As for this subject, civil engineering has a social responsibility. The internet is replete with examples of how this is achieved. I will not address the straw man fallacy you’ve presented. Providing an extreme example from a failed state bears little relevance to the discipline of engineering in a fully functioning democracy.
@⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻⸻ No, he is not correct and neither are you.
I love hearing an in-depth explanation straight from an engineer!
Thanks for your whole series. My son is an EE (Purdue) and that field seems the queen of engineering. Your series shows not so! For me you have taught me the big difference is scale: timescale and physical. You show CE works at huge physical scale as well designs that must perform over decades while having to deal with the interactions of disparate materials. These are lovely TH-cam videos. Also, you show me I mix my concrete way too wet! Keep up the great work!
I always find it interesting how old concepts are reused to make them new again. Wattle and daub was one of the earliest methods of building walls, used for at least 6,000 years. The wattle was basically like a wicker basket, bits of wood or sticks woven together to form a scafolding. Then the daub was applied, made of mud, sand, clay, and most-notably... straw.
The straw in wattle and daub provided the same function as the fibers in reinforced concrete. Reinforced concrete itself is very similar in concept to wattle and daub... Only steel instead of wood, and concrete instead of clay and sand.
Yes, wattle-and-daub walls made a very quiet home, and controlled humidity by absorbing it, then releasing it in dry weather.
I think it should be mentioned that while visible cracking of the concrete shown in the video is decreased, micro cracking (which will allow water incursion) is still happening. Concrete needs to be protected by a hydrophobic additive, sealing (paint, waterproofing e.t.c) or other means of long term care if uncoated reinforcing steel is going to be used in harsh environments, especially those that involve salts and standing water.
June 24th 2021. Oceanfront 12 story condo disaster. Talking about major concrete and rebar failure. How interesting this popped up.
When my dad made his home, he used concrete mixed with straw, rocks and rebar dipped in old engine oil. Don't know if you can do something like this today but this was 50 something years ago in the northern part of romania (summer+35, winter-25). he isn't here anymore, but the house is ...
I have never heard of straw in concrete. If concrete is done right in a house it is here to stay for a loooooong time
@@ThomasSiebenhofer Thomas Siebenhofer back then they didnt have fiberglass (well, they did but they could not get it because of Ceaușescu) so they used straw whitch has been used in mud huts in africa since the dawn of time and is increbily effective. not as effective as carbon or fiberglass but still better than only concrete. update, I went back to my fathers home in 25/01/2020, needs a bit of work on the roof but the walls are perfect.
@@vastianocara1792 straw is used all over the developing World and it works just fine.
@Plutarch Timbuktu Buildings made of clay and straw are still standing to this day, 500 years later.
@Plutarch the inspector would fail it because it doesn't fit with the standard not because it doesn't work. The role of the rebar network in a building is to defuse the tension (vibrations) all over the structure. In fact in Holland you'll see many walls made up only of (stainless) ebars and stones (no concrete) bound together within a metal grid.
A lot of the time rebar delivered to a construction site has a lime green protective paint coating on the surface of the metal. Unfortunately that’s not always the case.I often see bundles of strapped up rebar rusting off to the side of job sites.
I've never not seen rebar covered in rust, I've always suspected it was intentional for some reason
@@jedaaa I see it in green epoxy a lot however it’s sat there long enough that it gets rust spots
@@loadedfun4764 yeah and as soon as it starts getting manhandled around the site and scraped and scratched it seems like a futile endeavour, I've never seen it painted myself, perhaps that's not an industry standard here in the U.K
@@jedaaa google green epoxy rebar
This kind of video is exactly what youtube was made for. How would I ever randomly stumble upon the knowledge of rusting rebar
i wrote an important final exam today and this playlist really really helped, thank you sooooooooo much man, your work is amazing
Your beams were over designed. The steel rebars should fail first. just wanted to mention that! Please keep up the good work. Very nice channel.
Yes, plus they fail in shear when Im trying to demonstrate flexural cracks :) I hope the point comes across regardless
Isn't it preferable to see cracks *before* the structure comes down? In the range of at least two inspection intervals before it fails.
Steel fail in an explosive way, almost instantly, while concrete "let you know" in advance by the amount of cracking. If you need to keep an eye on structural integrity by easy examination, what would you prefer?
@@PracticalEngineeringChannel With a rig already set up like this, it would be cool to demonstrate the difference between under- and over-reinforced concrete beam failure and the safety consequences of each. I had this demo a while back in my civil program and it is quite a sight.
@@jekomac you got it backwards. Steel is ductile and stretches prior to failing. Concrete is brittle which is more explosive fail. The correct amount of steel is what will "let you know" when a structure fails.
Hmm, using fibers in concrete reminds me of the old clay castles in arabia where they used straw and other plant fibres to stop their clay from cracking... Old knowledge still seems to be the best!
Thanks for the video, i really like the concrete "series" and its nice to see a follow-up!
EDIT: Wisdom changed to Knowledge for definitions sake. (English is not my first language)
AcolyteArathok wisdom ain’t really the word you were looking for
I think its more like old ways combine with modern technology can solve problem in modern technology
AcolyteArathok and also did you know the word “improved” exists, it’s not that “old wisdom is the best” but that we _improved_ our ways of building once we discovered new materials
There is passive house design with uses exactly that method for flattening made of ponded sand and tiers. It is called Earthship.
Jamaludin B We _improved_ older technology
Basalt fibers are also starting to be used in concrete. They have many of the properties of the glass fibers, but they do not suffer from issues of high pH causing lack of binding or fiber damage and are more economical to produce. You can do some crazy things with a high strength mix and high levels of glass fiber reinforcement, like having bends in the final product, have high strength with light weight, and impact resistance. I am surprised that a company hasn't started making roof tiles out of the stuff since you could go thin like slate, but have immunity to hail damage. It isn't hard to get a mix for glass fiber reinforced concrete to be impermeable to water either, so you don't need the thickness that current concrete roof tiles have to keep the water out. They would also last longer than a slate roof since they would not suffer from broken slates, so we are looking at 50+ year roof life easily.
www.neuvokascorp.com
He does mention fiber and basalt composite rebar in the video you apparently missed hearing and seeing
Joshua79C C Yeah, I got a phone call at about that time in the video and couldn't hear the adio for about 20 seconds. Damn political donation begging.
Good continuation of your corrosion series.
Hi Grady, I was watching your videos, well done mate, great work, it is interseting that both of the fiber reinforced concrete beams that you tested failed in Shear rather than bending (which is expected due to the beam length to depth ratio and having NO shear reinforcement) I would suggest for the next test add some minor 6mm shear reinforcement near the supports, that would make the beam to go long way before failure. Thanks for the great work you are doing
One of the largest problems with fiber reinforcement that we have yet to find a solution to is early fault detection. A giant crack is easy to notice, tiny ones, not so much.
A beam can fail and still hold a load with traditional rebar reinforcements, but it doesn't appear to be possible to do that with fiber reinforcement
I was questioning just that while watching the video.
In literature (and practice probably), researchers are testing and using fiber optics to accurately monitor strains in concrete structural elements. That way it would be possible to see microcracks, providing the accuracy is high enough.
@@porschepanamera92 sounds expensive
Use a sonogram
@@BlackEpyon while that does work... how many bridges are in disrepair enough to get a fail without the use of fancy tech?
No mention of hot dip galvanized rebar? Still fairly cheap and much more resistant to damage than epoxy. In Bermuda we have lots of salt exposure and ungalvanized rebar is not allowed by the building code. Even the tie wire has to be galvanized.
Zinc (galvanized) coating is a sacrificial coating and will eventually allow rust
Zinc will last a long time if it's covered, you see it on older cars. It will go eventually but it lasts much longer than paint
Thanks for sharing this. It's always interesting to hear how things are done in different places around the world
The heat from the process dramatically reduces the strength of the rebar. When we send brackets for our elements to galvanization, it is always with normal round bars. The code for the industry (Eurocode) prohibits galvanization of rebar. I live in Denmark btw.
@@HepauDK definetly not dramatically. zinc has a very low melting point. most galvanisation processes take only a few seconds wich is barely enough to fully heat the rebar up. at least when done right of course
This ought to come in handy when I'm about to begin construction of my house. I had no idea about reinforced concrete! You live and you learn. Thanks!
Behind the house I lived in, in S.E. England, when I was a teenager, there was a 2 m high wood-reinforced concrete wall. I believe it was built in the early 20th or late 19th century. I'm not sure exactly when, but it was a long time ago. The wall is still there and still sound as far as I know.
How weird. Was thinking about rebar yesterday and saw this video in my recommendations today. Thanks for answering the questions I had but did not ask.
Great video but wanted to add something regarding corrosion. Although a much slower process, rebars in reinforced concrete members not subjected to marine environments or de-icing salts can still be subjected to corrosion via carbonation of concrete. Carbonation occurs due to atmospheric CO2 uptake and subsequent formation of new minerals (such as CaCO3), which do not provide this "protection layer" anymore and destroy the protective coating of rebars. Oddly, carbonation actually is beneficial to plain concrete, increasing its compressive strength!
As far as my knowledge in chemistry reaches, the CO2 alone actually can't corrode your steel, as the corrosion process itself, needs water. Concrete is alkaline, due to the amount of Calciumhydroxide in the mixture, wich can react with acids to form a salt of Calcium and water. The most common acid, is Carbonic acid, as this one can form by CO2 diffusing into water. So yeah, it isn't that much of an issue, since fluids diffusing through solids is horribly slow, and you can protect your concrete fairly easy by keeping it dry.
correct. concrete is a very porous material, so water and air have no problem finding the rebar, crack or no crack.
no oxygen, no rust.
@@cahdoge It is a problem that all concrete constructions will face, but if the rebar is placed correctly it's safe for 50 years.
A really great and instructive channel for all who are interested in reinforced concrete and Ideas of all kinds.
This bloke is the David Attenborough of the engineering world.
I've got to tell my plumber about crack control cause damn he needs it
It is only bad when he uses it to hold a hammer.
crack control costs money. You're already hiring a plumber, can you afford it?
Interesting that this showed up during the week of the Miami condo collapse…prayers to the families that lost loved ones…
Right
the algorithm knows
if the people build homes like the old ones (made with clay, stones and hay) emulating what in the video say (reinforced concrete with glass fibers) the buildings last more and are safer
The failure in the tests shown for those beams are both shear failures because they do not have any stirrups. Although the purpose of the test was to compare the differences between the cracks at the bottom. Great video!
Will you ever make a video on the Morandi bridge collapse in Genova (Italy)?
lol, I don't think he will be allowed to get near that structure... Politics and mafias in Italy mkay...!!!!
you won't be shooted at sight don't worry -_- maybe it's difficult to get technical documentation but because of burocracy
+Enrico Bonomi penso che sia stato ispirato a questo video proprio da questa triste storia.. e che la considerazione finale sulla mancanza di manutenzione non sia affatto a caso :(
Penso sia una coincidenza e non ci sia causalità fra il crollo e questo video, anche 2, 5, 6 mesi fa e oltre su questo canale si ' parlato di ponti, cemento, cemento armato, crolli etc, quindi è un filone di video iniziato ben prima che il ponte crollasse
AvE made a video about that with his analysis. th-cam.com/video/oLwf4_bXOc0/w-d-xo.html
I was vacationing in Greece in the early 80's. On a ferry boat leaving Piraeus, the travel guidebook said to look for an abandoned, deteriorating apartment complex along the outer edge of the harbor. *The concrete had been mixed with seawater*. It was seen as being emblematic of the corruption and crony capitalism of Greece.
Maybe the builders heard that roman concrete set harder with seawater?
My own experience of shitty concrete is a little less spectacular - my parents house was built on a hillside and during a cyclone in the 1980s (Bola) half the concrete structures holding the slope together failed, resulting in about an acre of hillside slumping into downhill neighbours' properties (expensive insurance mess all around)
It turned out that the builders had used illegally obtained river gravel and sand as the aggregate some 40 years previously - and it had a _very_ high silt content, weakening things considerably. One waterlogged hillside later, this was found out the hard way - and there also turned out to be a number of sites across the area which had been built built by the same cowboys and had the same problem - not good when one of the buildings was a small (3 floor) office block in large earthquake country - that building collapsed in a small magnitude 5.9 quake in 2003 that it should have easily withstood - thankfully no injuries as nobody was in or near it at the time (late evening on a Friday, holiday weekend) but that was sheer good luck.
I've not been on commercial job sites in decades but I can suggest that the craftsmanship is likely the number one problem with construction to be as per spec. I have witnessed residential construction as being very bad in following the just the minimum standards let alone doing the work in professional methods and following best practices in the trade. I have watched hundreds of concrete pours being made for decks, driveways, walkways, foundations etc. and most of the jobs rarely bother to use "dobies" to space the rebar, if it is used, 2" above a correctly prepared foundation. Most concrete work is poured right over bare soil, no sand, no quarter rock base, and finished especially with driveways and home foundations. See it all the time and folks wonder why there are big cracks vs. small cracks years later. As in this video, the one pump job that did use some dobies but not nearly enough of them had much of the rebar lying right on the yellow barrier so no concrete is getting under the rebar. BAD. Its a wonder that workers with that kind of concern for their work continue to get another job to do that again and again.
The old guys that knew the job are gone now mostly and the younger ones don't have a professional outlook. Also, the contractors are trying to come in quick, do the job, and get out. Make the most money, hire subcontractors who use illegals to cut cost and don't adequately supervise them.
The house I am living in was built in 1955, enlarged with a double car garage, which required a bigger driveway. They just left part of the old one, didn't use ANY seams in the new part, so now it is cracked drastically. The front porch has rebar stain on the concrete. Just about everything was done wrong in remodel and I continue to find more mistakes. House foundation not done right either.
I worked a summer doing concrete. Those concrete spacers pretty much tell you how to install them on their packaging or material provieded in the box. Clearly the guy who I was working for did not know or just did not care as he only used a few of them if any at all. I told him that you are clearly being paid to install concrete the right way and not his way. We were doing a finished concrete foundation and floor ( mono pour ) for a pretty nice house and he did not use any of the spaceres and the guy spent a lot of time grading and preparing the site along with insulation, forms and providing the drawings for the rebar. We show up and he tells us to lay out the rebar in a 2x2 pattern and leaves for a few hours. While we did this the guy had a workers lean too that you could look at the plans and had copies of everything including the rebar foundation. I looked at all of this stuff. When the boss got back I asked if this was how it was suppose to be and he said yes. So while he was not looking I snapped a few photos and we poured the concrete and finished it. I then went to the homeowner and showed him the photos. While we were working on the next job I was offered a much better job and took it. In the end the home owner threatened to sue him and he ended up having to to rebuild the entire foundation and slab. With all new plumbing and floor heat and everything to the exact specs. I am sure it cost him double or triple of what it should have. He no longer does concrete anymore and now is the county road and bridge main supervisor. I hate that guy as he cut so many corners. He did the same on a county remote shop which was my first job. I did with him.
@@kameljoe21 Seems to me the entire system of being licensed, having just anyone on the crew plus the inspections that are supposed to be catching the cut corners isn't working. Is Everyone on the take? Greedy state and local license, permits, fees, plan checks and corrections galore to satisfy the very people who allow cheaters to cheat for a bribe of some kind. All while the owners get screwed and the public are subject to more risk factors when entering buildings and using just any kind of structure. People are so absent minded about the years and years that will pass and this kind of activity will continue to put folks and owners at risk.
@@Garth2011 Oh did I forget to mention this was in rural areas where permits are not required and inspections do not exist. Put it this way where I live I can build a brand new house with out asking anyone. The only thing I have to abide by is building on my land and at least 10 feet away from the property lines. I own almost the whole block in a small town and I could build a shanty shack here if I wanted to. I have also been thinking about doing that. Building a super small cabins for hunters and renting.
@@kameljoe21 Seems fair...if the location has no codes/rules in the building of structures then its up to the builder to research and build a safe etc. building. Problem is, that is why building codes came about, your average building didn't care about the future, safety, efficiency etc. of what they had in plan. they simply just build it any old way but that puts people in risk, property at risk and much more. So that makes it all on the builder/owner...I hate to admit it but building codes get my vote long before I'd trust a Joe rural builder.
this channel is really helping me study during the summer before my senior year earning my civil engineering bachelor's degree, thanks
Could you possibly do some testing on fiberglass rebar? It costs less than steel right now, but cannot be used vertically.
Also if you can't find it with a minimum order of one, I can mail you smaller pieces.
what do you mean by vertically? as shear reinforcement? as far as I know, it can be used and it is actually heavily used in countries such as Canada where corrosion due to de-icing salts is a common problem.
What do you mean "cannot be used vertically"? I used to work for a place that made fibreglass rebar and one of the case studies (i.e. sales pitches) for it shows it being used vertically and horizontally with cast bends between the two.
Weird. I tied rebar for 20 years. Only used fiberglass rebar one time. And it was used in both vertical and horizontal directions.
Must be just the stuff I can get then. Maybe it's not thick enough.
Would be a good addition to talk about sacrificial anodes being "CAD welded" to the reinforcing steel
Meanwhile, latin countries required that the iron bars need to be treated with a polymer based coating to prevent corrosion.
The concrete formula needs to include hydrophobic component.
Please explain Hydrophobic layers to protect from corrosion.
That would be helpful.
And yes..adding fiber glass fiber, metal shard and granite or other minerals can help but it about the combination of these solutions.
Taught in every university: Planned obsolescence, skimping on materials and cost cutting. Companies are in business about quality but time and savings. Thus the majority will never get a quality built building or housing unless you do it yourself.
Could you make a Video about sugar in concrete?
Why happen, what happen?
Maybe it fits your series about this wonderful material.
sugar is a acid, cement is a alkali. im thinking it wont be sugar for very long,
Paul Kirkham
Ohh there happens magic.
It is much more amazing then that.
Maybe we will see it in a video some day.
I just know what happens but not why it happens. That's why I would love to see it here.
Civil engineers just love reinforced concrete
Probably the same way a pasty chef loves a nice cake.
Concrete gets me hard
*slaps roof of reinforced concrete structure* This bad boy can take some much stress before cracking up. Here is a table with all the information you need.
everybody loves reinforced concrete.
Except Trump, he loves marble and gold
They drink it and get really stoned...
All these old concrete and structural engineering videos are getting a lot of views this week.
Almost as if the predictive programming AI has steered your focus here? Look [here] not [there].
I used to work for a company that manufactured industrial paints and coatings called Tnemec. Their flagship product was a coating that prevents rust. It came about because one day the founder of the company noticed some rebar sticking out of old concrete rubble and noticed it wasn’t rusted. Long story short, they made a coating with cement in it which then had the rust inhibiting properties. The name Tnemec, is cement spelled backwards.
Tnemec makes all kinds of coatings for many things like zinc based coatings for water immersion service, water towers, coatings for bridge beams, sewer linings and even aerogel coatings for thermal insulating… pretty awesome stuff. The list is pretty impressive and I only named a few.
Pack your bag Mr Engineer you're going to the Surfside inquest.
Sad so many lives lost
This is an important video for me to watch at 2:38 on a school night.
My curiosity about the 'Florida's Condo Collapse' has brought me to this video!
Grady, thank you for another one of your excellent videos. Your explanation of concrete/rebar failure provides context for one of the possible failure conditions for the tragic collapse of the Champlain Towers South in Surfside, FL.