Boss Byproducts: Calthemites Are Man-Made Cave Dwellers

November 20, 2024 by Kristina Panos 6 Comments

Some lovely orange calthemite flowstone colored so by iron oxide from rusting steel reinforcing. Image via Wikipedia

At this point, we’ve learned about man-made byproducts and nature-made byproducts. But how about one that’s a little of both? I’m talking about calthemites, which are secondary deposits that form in those man-made caves such as parking garages, mines, and tunnels.

Calthemites grow both on and under these structures in forms that mimic natural cave speleothems like stalactites, stalagmites, flowstone, and so on. They are often the result of an hyperalkalinic solution of pH 9-14 seeping through a concrete structure to the point of coming into contact with the air on the underside. Here, carbon dioxide in the air facilitates the necessary reactions to secondarily deposit calcium carbonate.

These calcium carbonate deposits are usually white, but can be colored red, orange, or yellow thanks to iron oxide. If copper pipes are around, copper oxide can cause calthemites to be blue or green. As pretty as all that sounds, I didn’t find any evidence of these parking garage growths having been turned into jewelry. So there’s your million-dollar idea.

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That’ll Go Over Like A Cement Airplane

October 8, 2024 by Al Williams 37 Comments

Most of us have made paper airplanes at one time or another, but rather than stopping at folded paper, [VirgileC] graduated to 3D printing them out of PLA. Then the obvious question is: can you cast one in cement? The answer is yes, you can, but note that the question was not: can a cement plane fly? The answer to that is no, it can’t.

Of course, you could use this to model things other than non-flying airplanes. The key is using alginate, a natural polymer derived from brown seaweed, to form the mold. The first step was to suspend the PLA model in a flowerpot with the holes blocked. Next, the flowerpot gets filled with alginate.

After a bit, you can remove the PLA from the molding material by cutting it and then reinserting it into the flower pot. However, you don’t want it to dry out completely as it tends to deform. With some vibration, you can fill the entire cavity with cement.

The next day, it was possible to destroy the alginate mold and recover the cement object inside. However, the cement will still be somewhat wet, so you’ll want to let the part dry further.

Usually, we see people print the mold directly using flexible filament. If you don’t like airplanes, maybe that’s a sign.

Carbon–Cement Supercapacitors Proposed As An Energy Storage Solution

July 19, 2024 by Maya Posch 29 Comments

Although most energy storage solutions on a grid-level focus on batteries, a group of researchers at MIT and Harvard University have proposed using supercapacitors instead, with their 2023 research article by [Nicolas Chanut] and colleagues published in Proceedings of the National Academy of Sciences (PNAS). The twist here is that rather than any existing supercapacitors, their proposal involves conductive concrete (courtesy of carbon black) on both sides of the electrolyte-infused insulating membrane. They foresee this technology being used alongside green concrete to become part of a renewable energy transition, as per a presentation given at the American Concrete Institute (ACI).

Functional carbon-cement supercapacitors (connected in series) (Credit: Damian Stefaniuk et al.)

Putting aside the hairy issue of a massive expansion of grid-level storage, could a carbon-cement supercapacitor perhaps provide a way to turn the concrete foundation of a house into a whole-house energy storage cell for use with roof-based PV solar? While their current prototype isn’t quite building-sized yet, in the research article they provide some educated guesstimates to arrive at a very rough 20 – 220 Wh/m³, which would make this solution either not very great or somewhat interesting.

The primary benefit of this technology would be that it could be very cheap, with cement and concrete being already extremely prevalent in construction due to its affordability. As the researchers note, however, adding carbon black does compromise the concrete somewhat, and there are many questions regarding longevity. For example, a short within the carbon-cement capacitor due to moisture intrusion and rust jacking around rebar would surely make short work of these capacitors.

Swapping out the concrete foundation of a building to fix a short is no small feat, but maybe some lessons could be learned from self-healing Roman concrete.

Concrete Clears Its Own Snow

March 24, 2024 by Bryan Cockfield 25 Comments

Humans are not creatures well suited to cold environments. Without a large amount of effort to provide clothing, homes, and food to areas with substantial winters, very few of us would survive. The same is true of a lot of our infrastructure since things like ice, frost heave, and large temperature swings can all negatively impact buildings, roadways, and other structures. A team at Drexel University in Pennsylvania has created a type of concrete they hope might solve some issues with the material in cold climates.

Specifically when it comes to sidewalks and roadways, traditional methods of snow and ice removal such as plowing and salting are generally damaging to the surface material, with salting additionally being damaging to vehicles. Freeze-thaw cycles aren’t kind to these surfaces either. This concrete, on the other hand, contains a low-temperature liquid paraffin which releases heat when it has a phase change, from a liquid to a solid. By incorporating the material into the concrete, it can warm itself as temperatures drop, maintaining a temperature above freezing to melt ice and snow. The warming effect isn’t indefinite, but lasts a significant amount of time during testing.

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Making A Concrete Sign

October 14, 2023 by Jenny List 18 Comments

While paging through the feed a few days ago our attention was caught by something a little away from the ordinary in Hackaday terms, a DIY video about creating cast concrete signage from [Proper DIY] which we’ve placed below the break. A deceptively easy-looking mould-making process has a few tricks that will make the difference between a hard-wearing sign that lasts for years, and a lump of concrete.

So, to make a cast concrete sign, you throw together a mould with some letters, and chuck in some concrete? Not so fast, because the key appears to be preparation, and ensuring that there are no 90-degree corners on the mould parts. The letters are carefully shaped and sealed with varnish before being attached to the mould with silicone adhesive, and all the corners are beveled. Finally a light oil is used as a release agent, and hefty vibration takes care of any air bubbles.

The result is a set of signs, but we can see these techniques finding uses outside signage. For example, how about casting using a 3D printed mould?

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Miniature Concrete Hoover Dam Is Tiny Engineering Done Right

April 21, 2023 by Lewin Day 13 Comments

Growing up, we got to play with all kinds of things in miniature. Cars, horses, little LEGO houses, the lot. What we didn’t get is a serious education with miniature-sized dams. This recreation of the glorious Hoover Dam from the [Creative Construction Channel] could change all that for the next generation.

The build starts with the excavation of a two-foot long curve in a replica riverbed. A cardboard base is installed in the ditch, and used as a base for vertical steel wires. Next, the arch of the dam is roughed out with more steel wires installed horizontally to create a basic structure. The cardboard is then be removed from the riverbed, with the steel structure remaining. It’s finally time to pour real concrete, with a foundation followed by the main pour into foam formwork. The dam is also given 3D printed outlets that can be opened to allow water to pass through — complete with small gear motors to control them. The structure even gets a little roadway on top for good measure.

The finished product is quite impressive, and even more so when the outlets open up to spill water through. Such a project would be great fun for high school science students, or even engineering undergrads. Who doesn’t want to play with a miniature scale dam, after all? Bonus points if you build an entire LEGO city downstream, only to see it destroyed in a flood.

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Self-Healing Concrete: What Ancient Roman Concrete Can Teach Us

April 3, 2023 by Maya Posch 30 Comments

Concrete is an incredibly useful and versatile building material on which not only today’s societies, but also the ancient Roman Empire was built. To this day Roman concrete structures can be found in mundane locations such as harbors, but also the Pantheon in Rome, which to this day forms the largest unreinforced concrete dome in existence at 43.3 meters diameter, and is in excellent condition despite being being nearly 1,900 years old.

Even as the Roman Empire fell and receded into what became the Byzantine – also known as the Eastern Roman – Empire and the world around these last remnants of Roman architecture changed and changed again, all of these concrete structures remained despite knowledge of how to construct structures like them being lost to the ages. Perhaps the most astounding thing is that even today our concrete isn’t nearly as durable, despite modern inventions such as reinforcing with rebar.

Reverse-engineering ancient Roman concrete has for decades now been the source of intense study and debate, with a recent paper by Linda M. Seymour and colleagues adding an important clue to the puzzle. Could so-called ‘hot mixing’, with pockets of reactive lime clasts inside the cured concrete provide self-healing properties?

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