I love that this is a week-long research project/workshop for high school seniors. I know that we don't do anything nearly that intensive in our material science course at Princeton - partially because of time constraints and partially because we don't have anything that would test concrete's compression strength with any accuracy.
Does anybody know of similar experiences that near you that we could recommend for our high school students?
It's tough to repair a building that is a single piece of material.
That's the short answer to the rhetorical question posed in the video's title, though the host goes into a lot more detail than that simple sentence.
He also explains that making a house out of a single material defeats the purpose of using different materials on the inside (drywall, for example) and outside (bricks or siding, for example) of the house; that no single material will work for walls, doors, and windows necessitating the merging of the 3d printed materials with some sort of additional structure for those features, partially defeating the advantages of 3d printing; and the 3d printed house's size is restricted by the size of gantry on which the 3d printer moves.
I subscribe to Stewart Hicks's channel, primarily covering architecture and focusing on the Chicagoland area with a frequent highlighting of Frank Lloyd Wright's work. Most of the videos aren't on material science but rather on the architecture.
Today's fascinating, possible miraculous composite: ferrock.
From CertifiedEnergy...
Ferrock is created from waste steel dust (which would normally be thrown out) and silica from ground up glass, which when poured and upon reaction with carbon dioxide creates iron carbonate which binds carbon dioxide from the atmosphere into the Ferrock.
Roughly 95% of the Ferrock is made from recycled materials, Ferrock is both stronger and more flexible than normal Portland cement, allowing it to be used in highly active environments where there is a consideration for seismic activity.
From ScienceDirect...
At 28 days, the strength of Ferrock concrete exceeds that of conventional concrete by 13.5 percent for compressive strength, 20 percent for split tensile strength, and 18 percent for flexural strength.
From the University of Arizona...
"This all started from an accidental discovery in a lab, which is actually the way it usually goes," [Ferrock inventory David] Stone says. "That was back in 2002, and I included as much as I knew in my doctoral dissertation. But the work goes on. It has taken years to get just a basic understanding of the chemistry involved. But this shouldn’t be surprising, since scientists are still trying to figure out Portland cement and they’ve had 200 years.
"I am into this for the long haul. Time is on our side, since in this era of global warming unsustainable processes like cement manufacture will have to give way to greener alternatives."
As always, I am guardedly hopeful but skeptical until I start seeing Ferrock showing up in buildings.
I'm approximately a million hours away from being a structural engineer, but I think I could look at the cracks shown in the video at 6:49, 10:47, and 16:20 and say that maybe they shouldn't be going ahead with moving the bridge into place.
I never would have thought of the shifting forces during the movement of the bridge from its initial fabrication location, but the need to constantly restress the concrete with each move is fascinating. I would think that would require the concrete to be stressed and stressed and eventually over-stressed.
I ranted last week about the lack of 5-10 minute YouTube videos, so I won't rehash that grumble pile this week.
Instead I'll mention that there's an urban myth (frequently disproven) that construction workers on the Hoover Dam either fell into an couldn't get out of or were purposefully dumped into the un-set concrete used to create the dam itself.
"No, they weren't," is the short answer. The long answer has to do with the inhumanity of such a practice, the long set time of concrete, and - as this video above shows - the high density of wet concrete.
Today's video sees Dr Derek in a wetsuit trying to fill a sphere with himself and a batch of wet concrete while cutting back and forth to various explanations as to the science of concrete, the most widely used material we have and the underlying backbone of our modern world.
And at about 9:30 we get the clear explanation as to why bodies were never sunken in concrete: bodies float in concrete.
Yes, the rest of the video is well done, explaining the history of concrete - primarily around the Roman discovery, the science of concrete setting, slump testing, ingredients in different concrete batches, clunkers, the environmental effects of concrete production, cement v concrete, and much more.
It's a great, great video.
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| Source - bbc article |
Today's article describes an attempt to solve the sand shortage - at least partially - as well as to use some of the seemingly endless supply of plastic trash that we continue to produce in our world by replacing some of that sand with ground up plastic pieces.
There isn't much detail, and I would want to know a few things before considering plastic as a sand alternative...
Concrete is great in compression, very strong stuff.
Concrete isn't so good in tension, however, so using any concrete slab in such a way that it will experience bending load - as a cantilever, for example, or a flooring slab with a long span - requires something to address that weakness in tension.
The most common solution is simple rebar...but then there's the prestressed option.
In the above video - the first in a series of twelve Shay Murtagh videos exploring prestressed concrete beams in great depth - explains what prestressed concrete is and why it's strong than just reinforced concrete.
In case you aren't aware of Shay Murtagh, they seem to be a company with at least 100 employees - many but not all of whom can line dance.
Grady is back to school us about those tiny 'sparks' that flew away from the launch pad when SpaceX's rocket launched in November 2020.
Apparently the concrete that SpaceX uses for their launch pad isn't quite the same as the concrete that sits as the walkway outside my classroom window.
Grady explains what concrete is (hydrated crystals) and then tests two types of concrete exposed to three heat environments (room temp, home oven, and propane torch) under compression strength tests.
Not shockingly, the heated concretes broke at way less force.
He then goes on to explain how most of this weakness is caused by our old nemesis: thermal expansion.
I feel bad for this youtuber having to broadcast to us from some sort of white void with bad lighting or white balance without understanding how low quality his image is compared to the quality of the images that he's sharing 'behind' him. And I don't know why he won't make eye contact with me. He keeps looking at something above and in front of me that I can't see.
Sorry for the snarkiness.
I've been watching a lot of very professionally made YouTube videos recently, and it's easy to see how much better those look than this more amateurishly produced videos, but I will admit that this guy gives a great explanation of why epoxy coated rebar is used (corrosion prevention), the problems with it (the epoxy rubs off unless the rebar is handled very gently before sealing it in concrete leading to pitting corrosion and debonding), and pros and cons of possible solutions (high costs due to scale production and lack of building code acceptance).
It's easy to think that simple solutions (just paint the rebar) won't lead to secondary problems (the paint rubbing off).
(Oh, and respect to BadLandsKid who had the top comment on this video when I accessed it most recently, "Very galvanizing topic. While it’s not set in stone, it reinforced my views on rebar.")
Does this really?
Does this really change everything?
Like is it now less likely for a lost Lego brick to find the bottom of my foot in the dark at midnight?
No? Then it doesn't change everything.
I like the idea of using old tires to supplement the gravel road bed to keep things in place before paving over them. It seems like a great use for old tires and certainly keeps them out of landfills.
But calling them an 'industrial-strength geosynthetic confinement' technology seems a little jargonish to me.
That's it. That's the answer.
It's a composite stone made of compressed seashells with carbonic acid leaching out calcium out of the shells to fuse them together into stone.
The above video, from the US National Park Service, explains the material of the walls of Castillo de San Marcos and how its porosity was both a weakness (it needs to be plastered to waterproof it) and a strength (the walls could 'absorb' cannon balls fired at it in an attack.)
The second video - below - explores the preservation efforts necessary to maintain the coquina walls.
CarbonCure works with existing concrete factories to simply add CO2 without changing the concrete recipe or machines. CO2 is collected from smokestacks of large polluters like coal power or cement plants and brought to the concrete factory for recycling. Our proprietary technology injects the CO2 gas into the concrete where it is converted into more stone within the concrete......I find myself skeptical as to just how we get benefits without any downsides at all.
The best part is that it costs about the same and it keeps the same good looks and durability that you're used to with regular concrete.
It's green concrete without the trade-offs.
CarbonCure's system takes captured CO2 and injects it into concrete as it's being mixed. Once the concrete hardens, that carbon is sequestered forever. Even if the building is torn down, the carbon stays put. That's because it reacts with the concrete and becomes a mineral.Again with the extraordinary claims. I'm going to need a little more detail.
...
"The best thing about it is the mineral itself improves the compressive strength of the concrete," Christie Gamble, the director of sustainability at CarbonCure, told CNNMoney."
The technology may be used to increase the compressive strength performance of a concrete mix. The strength improvement can then be leveraged in the optimization of the mix design for a specific end goal[.] (source)I hope that this technology is as perfect as is suggested, but I'm not holding my breath.
...
Once injected into the wet concrete mix, the CO2 reacts with calcium ions from cement to form a nano-sized calcium carbonate mineral that becomes permanently embedded in the concrete. (source)
Previous work had revealed lime particles within the cores that surprisingly contained the mineral aluminous tobermorite – a rare substance that is hard to make.And it looks like the Romans knew what they were doing.
The mineral, said Jackson, formed early in the history of the concrete, as the lime, seawater and volcanic ash of the mortar reacted together in a way that generated heat.
But now Jackson and the team have made another discovery. “I went back to the concrete and found abundant tobermorite growing through the fabric of the concrete, often in association with phillipsite [another mineral],” she said.
She said this revealed another process that was also at play. Over time, seawater that seeped through the concrete dissolved the volcanic crystals and glasses, with aluminous tobermorite and phillipsite crystallising in their place.
These minerals, say the authors, helped to reinforce the concrete, preventing cracks from growing, with structures becoming stronger over time as the minerals grew.
As the authors note, the Romans were aware of the virtues of their concrete, with Pliny the Elder waxing lyrical in his Natural History that it is “impregnable to the waves and every day stronger”.If you want to read more, check out the original research article...or the Guardian article that's way more readable and that I quoted up above.
