Does Rebar Rust?

First line of the video: "Concrete reinforced with steel is the foundation of our modern society". I love this guy.

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.

This video could not been more important than today with building collapse in Surfside Florida. Look no further than this video. Thanks.

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.

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.)

So basically hummanity went from making mud and straw structures to fiber reinforced concrete. Same concept, higher tech.

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.

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.

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.

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.

Might be time to revisit this topic, sir.

I like that you reinforce your videos with concrete data. Even if the measurement system is a bit rusty.

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".

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 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.

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.

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.

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!"

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.