Concrete may have found it's killer app in graphene - cklife https://arstechnica.com/science/2018/06/the-secrets-of-concrete-may-have-found-its-killer-app-in-graphene/ ====== conistonwater The article does a terrible job of explaining the nature of the problem, but the summary is that concrete makes a lot of use of aggregates of rock which are often of sub-optimal size distribution, in particular because these are not always readily available in ready-sized form. Making aggregates from rocks of larger sizes, particularly aggregates of rocks which are used for the size distribution of gravel, or making aggregate sized particles from a gas in a particle reactor, are two ways to solve this problem. On the problem of concrete's energy use: A large part of the energy used by concrete in heating the aggregate to its boiling temperature comes from the rock's own cohesive energy, which could be released using less energy. ~~~ stcredzero _A large part of the energy used by concrete in heating the aggregate to its boiling temperature comes from the rock 's own cohesive energy, which could be released using less energy._ My understanding is that the heat energy from the heating that this article is about came from the sun. ~~~ jimmy1 This doesn't sound right to me. I know it's not as simple as putting some chemical or material or something in to a concrete mix but I have a pretty strong intuition this isn't what's happening here. What I would think would happen is that the concrete, or at least the aggregates, would reflect more heat from the sun on warmer days due to a more metallic, mirror-like surface resulting from the heating of the concrete. If it helps to make the point more clearly, think of how a solar water heater works. A cheaply made one may be insulated, but it will not use a heat conductor. A more expensive one will have a heat conductor, but the design often incorporates a plastic outer coating to keep the conductor from becoming too hot, making the whole thing more reflective. You can get a more concrete comparison in a home air conditioner. In a window air conditioner, the design will look similar to a cheap plastic case but be more reflective. In the windowless A/C that you likely have in a house, the outer casing will be coated in a far more reflective material. The more reflective surface will allow for more sunlight to pass through the unit and heat the room at the same time. I think this isn't just some magical idea about how concrete absorbs heat. I think this is very real. You can see it in the construction process of a concrete building, where it is necessary to build a scaffold over the cement slurry. This is done to prevent the heat from the heating of the cement from causing the "raw mix" to heat up too quickly. ~~~ hinkley I know of a place in China where they were doing a lot of solar photovoltaic installations. They would find this patch of dirt and cover it with concrete and set up a nice big heliostat for tracking. I worked there for three summers. I tried going around during lunch but nobody else wanted to. It took a bit of walking to get from one side of the project to the other. So these guys were building these giant solar heliostats that were only at their peak output for an hour or so. Their biggest problems were: 1\. It wasn't hot enough and was causing a lot of stress on the electronics. They were doing workarounds but they would only save a percentage of their energy. 2\. It was too big and too expensive to make. They would get it up and running, then wait too long and lose energy production. Concrete is the obvious material that can be brought up to a working temperature as quickly as you want, then cooled down without any mechanical intervention. You could run an entire house off of the heat alone. ~~~ tasty_freeze >It wasn't hot enough and was causing a lot of stress on the electronics. How did they do that? How can you tell if it is the concrete temperature that is the issue, or the electronics temperature? ~~~ hinkley The panels didn't get hot enough on a particular sunny day (but those are rare, they happen, usually on overcast days. This place is in the mountains and a big foghorn is a daily annoyance). One morning the guys came over to me and asked me to check our array, that they thought they had found a problem. I grabbed the top two sensors, turned them around and pointed them at the concrete slab (just in front of my desk) and asked how hot they were. They were up there in the 30s, which was hot enough to fry the electronics. So what had happened was that they had been out there setting up the concrete for another two weeks and the concrete was just shy of the point where the panels stopped generating a significant amount of energy. So they opened up the scaffolding, put the modules in, and the concrete had barely come up to the bottom of the box. The concrete was hotter than it would have been otherwise, but the electronics were in their breakpoint zone. ~~~ pfdietz The concrete probably would have been hotter had it taken the full 12 hours to reach 200° C. There's probably a complex tradeoff between concrete strength and temperature in the curing process. ~~~ hinkley They had taken a couple of days off that last day. It was a pretty good technique. They mixed it before work and had it ready to pour by the time they got to work. It was really, really well prepared. ~~~ pfdietz I suspect the concrete was prepared, but its use was compromised by the fact that the concrete was poured into a pre-heatshed, so that it wasn't reaching the peak temperature for long. ~~~ hinkley I suspect you are right. My memory is a bit fuzzy, it was a while ago. ------ shkkmo > "It turns out graphene is also able to reflect some of the solar radiation > hitting it, keeping it cooler and saving energy. But on its own, graphene is > just an inert material, says Yaroslav Barabanov, a physicist at the US > National Renewable Energy Laboratory in Golden, Colorado. It takes only a > modest boost from adding metal particles to give it enough energy to become > self-lubricating, however." Huh? Can someone elaborate what he's talking about? How would this work? What particle type, in what amount, does what? ~~~ bregma I think they mean metal particles that do not bind too strongly to the concrete, and/or that are small enough to not form particles with diameters larger than the micro-slit of the aggregate. Or something like that. But a good explanation would help. I have a suspicion that the amount of "particle type" is probably the wrong word to use. Any metal particle with a melting point lower than that of concrete (typically 1300 deg C) should do the trick. ~~~ shkkmo Ok. I'm going to do a bit of experimentation then. I want to create my own graphene and see what I can do. ------ dandare It reminds me of those solar thermal collectors that resemble a giant asphalt/concrete rooftop. [https://en.wikipedia.org/wiki/Solar_thermal_collector](https://en.wikipedia.org/wiki/Solar_thermal_collector) ~~~ mr_overalls Solar Turbines, which I've seen a lot in the southwest, really have the same concrete feel: [https://en.wikipedia.org/wiki/Solar_turbine](https://en.wikipedia.org/wiki/Solar_turbine) They remind me of huge (but thin and bendy) sheets of corrugated steel. ~~~ TheOtherHobbes A friend in construction and engineering calls them "fat steel tubes" and says they're inefficient, and they're expensive. I've never been able to find out if this is true or not. What does happen is that you can sometimes sell a big roof collector for $250,000, so that adds to the cost of the solar company's margin. The whole business is weird. There's something about selling something slightly more valuable than gold that seems incredibly profitable, and there's no way to price that into conventional models of revenue, so it becomes an amorphous black box. ------ cwkoss Interesting. I wonder how large the materials were, and