Martian Rammed Earth

长期以来，人类在火星上的长期探索（并最终定居）一直是一个雄心壮志，随着私人太空公司的崛起和越来越多的成功数据检索任务，曾经是理论上的前景现在正在迅速成为一个看似合理的现实。为了实现这一目标，需要建立庇护所和基础设施，需要建筑材料用于暴露在火星大气层以及可居住环境中的结构。自然，从地球运输散装建筑材料是不可行的，因此已经提出了一些潜在的解决方案，从充气栖息地到地表下的结构。原位资源利用已经获得了相当大的牵引力，并且已经研究了各种形式的这种形式，例如火星混凝土和3D打印风化层，尽管这些需要添加剂和/或能源密集型工艺。事实上，这个太空时代问题的更理想的解决方案可能是最古老的建筑形式之一：夯土。作为一种可持续的建筑材料，夯土已经出现了一些复苏，人们对理解其强度和耐久性的来源的兴趣也重新燃起。特别是，最近的研究已经模拟了作为一种非饱和土壤的夯土，指出了一个“孔隙吸力”，发展作为夯土干燥和平衡与周围环境。这类似于在干沙中加入少量的水就可以在海滩建造沙堡。遗憾的是，没有人能够将火星风化层（土壤）的样本带回地球，但由于探索性探测，人们对覆盖火星表面的物质成分有了很好的了解。这些信息已被用于从地球上存在的材料中复制或模拟火星风化层。这些模拟物对于测试NASA于2020年登陆火星的Perseverance漫游者原型至关重要。一些先前的研究已经使用风化层模拟物进行了撞击地球火星风化层的潜力，但以前的工作没有调查火星大气和重力对产生的材料的影响。地球上的夯实地球与其所处环境达到平衡的方式对它所表现出的强度至关重要，这同样适用于火星。因此，至关重要的是在现有条件下测试夯土，以了解这种技术是否适用于建设火星基础设施。因此，该项目将研究如何在火星上制造冲压地球，以及其可能的机械性能将在原地。这将通过测试模拟火星土壤的样品来实现，这些样品被压缩成块，并受到火星大气和重力条件的影响。这样做是非常具有挑战性的，因为火星的大气压力非常低（大约是地球气压的1-2%），最高温度为20摄氏度（但可以下降到冰点以下50多度），空气中95%是二氧化碳。更难模拟的是火星上的低重力（大约是地球上的三分之一）。该项目将模拟大气室中的大气压力、温度和空气成分，并在其中确定材料特性。火星的重力条件无法完全复制，但将在土工离心机中的高重力水平和微重力下进行自由落体实验，这些信息将用于推断火星上的材料性能。该项目将确定在火星上使用夯土建造的可行性和基本工具，并将为今后的研究和开发工作奠定基础，研究最佳结构形式和建造技术，以建造火星结构和基础设施。

Extended human exploration (and ultimately, settlement) on Mars has long been an ambition, and with the rise of private space companies and increasing numbers of successful data-retrieval missions, what was once a theoretical prospect is now rapidly becoming a plausible reality. For this to be realised, shelter and infrastructure will need to be established, requiring construction materials for structures exposed to the Martian atmosphere as well as within habitable environments.Naturally, transporting bulk construction materials from Earth is unfeasible and so a number of potential solutions have been suggested, ranging from inflatable habitats to below surface structures. In-situ resource utilisation has gained considerable traction and there has been research into various forms of this such as Martian concrete and 3D printed regolith, although these require additives and/or energy intensive processes.A more ideal solution to this space-age problem may, in fact, be one of the most ancient forms of construction: rammed earth. Rammed earth has seen something of a resurgence as a sustainable building material and interest in understanding the sources of its strength and durability has been renewed. In particular, recent studies have modelled rammed earth as an unsaturated soil, pointing to a "pore suction" that develops as rammed earth dries out and equilibrates with its surrounding environment. This is similar to the way that adding just a small amount of water to dry sand allows sandcastles to be built at the beach. Sadly, no one has been able to bring samples of Martian regolith (soil) back to Earth but thanks to exploratory probes a good understanding of the composition of the material that covers the Martian surface exists. This information has been used to make replica, or simulant, Martian regolith from materials existing on Earth. These simulants have been vital for testing the prototype of the Perseverance rover that NASA landed on Mars in 2020. Some previous research has been conducted into the potential of rammed earth Martian regolith using regolith simulants, but this previous work did not investigate the effects of the Martian atmosphere and gravity on the material produced. The way that rammed earth on Earth reaches equilibrium with the environment in which it is situated in is crucial to the strength it exhibits and the same will apply on Mars. It is therefore vital to test rammed earth under the prevailing conditions to understand if this technique is viable for building Martian infrastructure. This project will therefore investigate how rammed earth can be made on Mars and what its likely mechanical properties will be in-situ. This will be achieved by testing samples of simulated Martian soil, compressed into blocks and subjected to Martian atmospheric and gravity conditions. Doing so is very challenging as the Martian atmosphere is very low pressure (around 1-2% of the air pressure on Earth), the maximum temperature is 20 degrees Celsius (but can drop to more than 50 degrees below freezing) and the air is 95% carbon dioxide. Harder to simulate still is the low gravity on Mars (around one third of that on Earth). This project will simulate the atmospheric pressure, temperature and air composition in atmospheric chambers, within which the material properties will be determined. Martian gravity conditions can't be replicated exactly but tests will be conducted at high levels of gravity in a geotechnical centrifuge and at microgravity by doing experiments in free-fall and this information will be used to extrapolate the material performance on Mars. This project will establish the feasibility and fundamental tools to build using rammed earth on Mars and will lay a foundation for future research and development work investigating optimal structural forms and construction techniques for the creation of Martian structures and infrastructure.