I guess, this would fail fail on any material properties we use cement for in various flavors of concrete in the first place. Also, the building material is concrete, not cement. Cement is just one ingredient.

(It's kind of sad that a publication like Science would mix these up. A road made from cement exclusively would be blown away in a minute. Cement is [just] a binding agent for the aggregate.)

FYI had you read the article, you'd see that they use cement/concrete accurately throughout, and are accurate in their usage of cement in the title.

One such quote, although it's throughout the article

> The problem is that cement, a primary ingredient in concrete, is normally a poor electrical conductor. So, in recent years, several groups have made structural supercapacitors by spiking cement with highly conductive forms of carbon, such as graphene or carbon nanotubes. Although these perform well, the ingredients are expensive and hard to produce in the massive volumes used in the cement industry, notes Franz-Josef Ulm, a civil engineer at the Massachusetts Institute of Technology (MIT).

But, how and why do you jump from what is to all assumptions an interesting surface material to building structures? Also, most capacitors are phono-sensitive, meaning they react to contraction and tension and all kind of vibrations, which wouldn't suggest load bearing masses as a prime candidate for this, even if the doping added to the cement didn't have any effect on the material properties. Let alone the practical problems of having significant charges in any structure, like a road or a building.

So here's some more article quotes lol

> Ulm and his team mixed a small percent of carbon black with cement powder and added water. The water readily combines with the cement. But because the particles of carbon black repel water, they tend to clump together, forming long interconnected tendrils within the hardening cement that act like a network of wires.

> Ulm and his colleagues cut this wired cement into small plates, creating supercapacitors 1 millimeter thick and 1 centimeter wide, about the size of a button. After adding a membrane, an electrolyte made from potassium chloride—a simple salt—and water, the researchers sealed the sandwich structure. When they then connected a wire to the plates and flipped a switch, cement supercapacitors lit up a series of LED lights.

> To succeed, researchers will need to scale up the button-size plates. Doing that isn’t trivial, Nguyen notes. As supercapacitors get larger their electrical conductivity typically declines, making it harder to inject and extract energy from them. One solution, Ulm notes, is to simply add more carbon black to the mix—but not so much that it weakens the structural integrity of the cement. For structural concrete, the researchers found they could add up to 10% carbon black without compromising too much of its strength. Ulm says the group has patented its technology and is now working to scale it up to match the output of a 12-volt car battery.

They are well aware of the concept of structural integrity and of course the big challenge is scaling up their idea in a way that does not compromise it.

It's somewhat hard to believe that this (forming lumps and adding membranes) does not affect the material properties as building material, especially, where various flavors of concrete are all about the grade of the cement. (Concrete isn't just concrete.) How is this, as a capacitor, immune to pressure? How do you jump from a 12V car battery to entire buildings and roads?

Retaining the structural strength of the cement itself does nothing about the fact that you've introduced a big lubricated slipface into the structure, namely the membrane.

Here's my best idea: You pour regular reinforced concrete in sort of a waffle pattern, make a bunch of capacitor cells in the holes, then put another layer of concrete on top. The individual membranes have limited shear stress. Leaks are isolated. Presumably cells of mostly concrete and water still have pretty good compressive strength, so maybe it will hold together like that. I'm guessing you at least have to increase the total slab thickness, though.

I'm guessing there will be some kind of creative architecture like that before it goes to prod, anyway.

I would think that the membranes would also be the reinforcement. Though I am not getting a good picture in my head from the description. It has to be practical. Mix concrete, pour concrete...the same way we do it now. There is roomm for skilled labor at the reinforcement phase which is a precision bit of construction that is inspected closely before pouring.

Yes, and the article didn’t touch upon that at all. Building a home foundation that would shake apart in a windstorm is a non-starter.

You could be hitting on something here. Instead of pouring monolithic you could use prefab blocks that are filled in. I have used that technique to repair a caved basement where cinder block replacements were filled with concrete and rebar.

There is a similar system using foam blocks that act as forms and are left in place. Menards sells them (and may own the manufacturer).