A group of boffins from the University of Manchester have proposed an innovative if unexpected way of creating structures for any future Mars colony: mixing the bodily fluids of the first colonists with Martian soil to create super-strength concrete.
The method, published in the journal Materials Today Bio, reflects the difficulty and cost of transporting building materials over the vast interplanetary distances that would be involved in any future Martian settlement project.
Transporting building materials from Earth to Mars would require extraordinary expenditure – one estimate suggests that it would cost as much as $2m per brick – as well as a considerable increase in the logistical complexity of any mission. The obvious solution would therefore be to create structures from materials already present on the Martian surface, a technique known as in situ resource utilisation (or ISRU).
"Scientists have been trying to develop viable technologies to produce concrete-like materials on the surface of Mars, but we never stopped to think that the answer might be inside us all along," Dr Aled Roberts of the University of Manchester and project co-author said in a Manchester Uni news release.
Mars is not short of loose rock and dust on its surface (material collectively known as regolith) and this could be easily used as an ingredient to create concrete. Water is also present on the red planet, and although it is not handily available, it's not beyond the realm of possibility that it may eventually be liberated from beneath the surface and used to make building materials as well as sustaining colonists.
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The authors studied the use of a protein called human serum albumin (HSA), which is present in blood plasma, as a binder to be mixed with regolith to create what the boffins described in the paper as extraterrestrial regolith biocomposites or ERBs. The results were impressive, as the paper states:
Employing a simple fabrication strategy, HSA-based ERBs were produced and displayed compressive strengths as high as 25.0 MPa [mega pascals]. For comparison, standard concrete typically has a compressive strength ranging between 20 and 32 MPa.
Even more helpfully, other human secretions proved to be similarly useful in the process:
The incorporation of urea – which could be extracted from the urine, sweat or tears of astronauts – could further increase the compressive strength by over 300% in some instances, with the best-performing formulation having an average compressive strength of 39.7 MPa.
"The mixture does contain about 70% water, but this water is recoverable," Dr Roberts told The Register. "Essentially the hardening process is driven by the materials drying out, so if you dried them out in such a way where you could re-condense the water then you’d be able to recover it. This is important because water is a precious resource on Mars."
This recovery process is very important and will be one of the drivers to build structures in the first place. Water will undoubtedly be brought from Earth, but it will be in limited supply as it is also extremely heavy and bulky. It also can't be left lying around as it would unhelpfully be in ice form for much of the time on the Martian surface, while in liquid form it would evaporate very quickly due to the thin Martian atmosphere.
Therefore settlers will have to build structures in order to maintain a steady climate in which water can be kept liquid, prevented from evaporating and potentially recovered from construction efforts.
The Martian blood-bricks have surprising strength due to a chemical process in which proteins in the blood reorganise themselves into "a densely hydrogen-bonded, supramolecular β-sheet network – analogous to the cohesion mechanism of spider silk," which led the exo-architecture boffins to suggest that the HSA-ERBs would lend themselves to being 3D-printed. They also suggested that stocks of synthetic spider silk and the bovine equivalent of the human HSA blood protein could also be carried on the mission in order to provide a quick early construction starter pack.
One point which did occur to us was the possibility that the use of human bodily fluids means that astronauts could be exploited in the rush to erect early human settlements on Mars. While most spacefaring nations would consider crew safety to be paramount, there might be some where under extreme conditions political considerations might outweigh the safety of crew members, and individuals might be asked to give more than they safely could. Dr Roberts is hopeful in this regard, since he feels it would eventually be counter-productive.
"I imagine that the health and safety of the astronauts will be the top priority for any space mission – so I don’t imagine the technique being over-used for the sake of rapid habitat expansion," he said.
"If the technique is overused and it adversely effects the health of the crew it would be a disaster. However, the purpose of constructing buildings with thick walls and ceilings is to protect the health and safety of the astronauts (from radiation and meteor strikes) – so a compromise would have to be found somewhere. If they’re too cautious and don’t employ the technique enough, a solar flare or a meteor strike could cause a lot more damage," he added.
At this point, we at The Register formally propose that this technique should henceforth be known as the Churchill method, since it offers nothing but blood, soil, tears and sweat. We freely admit that Churchill did not mention urine in his famous speech of May 13 1940, but we feel it is implied due to the suggestion he was frequently pissed and may have been so when he delivered it.
Dr Roberts pointed out to us that the University of Manchester team went with the name AstroCrete, but he kindly added: "Please feel free to use the reference to Churchill." ®