Speaking of concrete in space...
For today's entry, I had the opportunity to speak with David Bemis. He is a cement quality technician a large cement factory located in Pueblo, Colorado. He did his graduate and undergraduate work in chemistry at Colorado State University, Pueblo. We had a chance to catch up this past week in a phone interview on the topic of concrete and its potential future in space. Space is the final frontier in more fields than one!
David, thanks for taking the time to talk about cement! Your interest in the chemistry of concrete apparently goes beyond the ordinary sorts we think of for sidewalks, roads and buildings we see everyday. Where else do you see concrete having applications?
Well, I'm really interested in concrete - concrete is an old technology and is still sufficient for our needs today. Cement is the powder... concrete has the aggregate and sand mixed with the cement... both are tied together Both [the cement and the concrete industries] are old school in their thinking. They've always done it this way. I'm seeing more change on horizon because technology has enabled us to understand it better, in more detail, and beyond 'we add water [and] it gets hard. Now, it's more engineered for specific strength and workability. Make a mix, lay it down, and have it be drivable at the end of the day. Or we can know it will be useable in six hours. Special mixes [are] designed for the application.
I recently watched Elon Musk's announcement about going to mars. Seeing all of this innovation lead me to the notion that ....Gawd... what about concrete on mars? Maybe it's because I'm in the business - if you are a hammer, everything looks like a nail - but maybe concrete is a good solution for space structures too.
When I studied it, I found that the basic research had already been done by scientist and engineer T. D. Lin. He was a researcher in materials science for PCA (Portland Cement Association.) T.D. Lin had the idea of making concrete on the moon. He worked on this far out idea on the side. It was during the 70s, after the last Apollo missions. He had this concept and wrote a proposal and was able to get 100 grams of moon regolith from nasa - actual dust rock and sand from the moon! He made concrete using that and a special calcium aluminate cement. His contribution to the science was to say that calcium aluminate works the best. He built small cubes and structures and did tensile and fletcher strength. The strength tests showed that the lunar dust actually works very well, in some ways like fly ash. It suggested that these things have a possibility of working. It was good enough that other people were interested, though that research has stagnated as people quit going to the moon.
That's fascinating! So, if you were to build on the moon, the lunar dust and sand would make a good aggregate. I usually think of concrete as a process that involves water... is that what we're talking about when you are considering concrete for space?
Because the [industry] is focused on hydration process of cement in concrete, that is initially where you would go as a way to build on a planet or in orbit or on the moon. Use the known chemistry and known issues. [The goal is to] engineer it so the water doesn't evaporate or so it can interact properly so that the proper chemistry can develop. So, on the moon, all your water issues are different because it's not earth.
I am interested in some alternatives to standard cement too. You can use pure sulphur as a cement; you melt it and mix with aggregates; it would crystalize and bind the aggregates and that is a waterless concrete.
You can also use solar power in the form of solar concentrators to just melt the lunar material together. Sinter it. This makes a strong solid and on the moon, where there is no moisture to degrade it, it would work very well.
What do you see as something cool in the future of concrete, either in space or here in earth?
3d printing is a big part of the future of concrete. There are already a few groups of people who produced concrete 3d printers. These systems use a concrete pump truck that pushes premixed cement into the machine. It's poured the same way a 3d printer with plastic is printed, a nozzle lays it out. Normal concrete generally doesn't harden or stiffen up... you have to use slump-loss concrete, concrete that has very little slump. Low slump loss concrete. One of the most expensive things about creating with concrete is form work. Building a building or a bridge, you have to build a mold and make sure it is water tight, concrete tight. Using 3D printing has the potential to eliminate the need for these forms.
Now, in terms of the steel reinforcements, the rebar that gets tied together, you would have to put it in during the printing process. Or the other thing could be maybe designing a concrete with additives with pins or glass fibers that add strength in the mix without needing so much steel structure. If it was for a house maybe it may be done entirely with an additive rather than with steel bar. Some advanced printing machine could even put down the steel structures during the process. NIST (The National Institute of Standards and Technology) has just announced a plan to investigate 3d printing of concrete. That's definitely where the future lies.