Martian Concrete could be key to future human colonisation on Mars
As engineers continue to evolve modern concrete on Earth, some materials scientists have taken their concrete visions one step further into space. Scientists led by Lin Wan at Northwestern University in the US developed the Martian concrete using materials that are available in generous supply on Mars and without using water, a resource that will be limited and precious on the planet.
The Northwestern team sought an alternative to the usual cement mix required to make concrete. They settled on a technology that has been in development since the early 1970s: sulphur-based concrete. The material is made by heating sulphur to around 240 degrees Celsius, mixing it with aggregate and allowing it to cool. However, this process has occasionally proved problematic, with the sulphur shrinking during cooling and causing cavities and internal stresses that weaken the final material.
Wan and team found that with an aggregate that emulates Martian soil (containing silicon dioxide, aluminium oxide, iron oxide and titanium dioxide) they were able to produce concrete two-and-a-half times as strong as the minimum compressive strength required for US building codes. Through testing, the team found that Martian concrete reached a compressive strength of 50 megapascals (MPa) or more, due to the strong chemical bonds sulphur makes with the Martian soil during curing. Standard concrete used in buildings has a compressive strength of about 20 MPa (below).
They also found that the mixture, composed of 50% Martian soil with a maximum aggregate of 1 mm in size, would hold together in the less dense atmosphere of Mars – circumventing problems that would be seen on the Moon, where the vacuum of space would cause the sulphur to sublimate into a gas, turning a structure into nothing more than a pile of aggregate. The atmospheric pressure and temperature range on Mars are adequate for hosting sulphur concrete structures.
NASA has been the inspiration behind the development of Martian Concrete. NASA’s Mars One strategy is to robotically construct a human settlement on Mars starting in 2025 with humans arriving five years later.
The design calls for a 3D-printable inner spherical shell and outer parabolic dome and an interior layout with separate wet rooms (lab, kitchen, bathroom) and dry rooms (bedrooms, workstations) to limit the resources needed for construction (refer Figure 3 below). Two hatch openings directly across from each other allow individual habitat units to be connected.
The layout was inspired by the NASA-funded Hi-Seas (Hawaii Space Exploration Analog and Simulation) project, a Mars flight crew training simulator. Machines and materials would be sent first to remotely create structures. Humans would follow and test and use the structures. Software company Oracle, Chicago architects Skidmore Owings Merrill and engineering firm ABB are on board as the system required to 3D print structures on Mars takes shape.
The UAE is also pushing ahead with its Mars programme. Its Hope orbiter robotic probe was launched on 19 July 2020 and will reach Mars in February 2021, where it will study weather cycles and investigate why the planet’s atmosphere is losing hydrogen and oxygen. The Mohammed Bin Rashid Space Centre is planning Mars Science City, working with architecture firm Bjarke Ingels Group on the design (refer Figure 4 below). It is hoped that the city, which will include 3D printed elements in its construction, will help scientists understand better the challenges to building a city on Mars by 2117, the UAE’s date by which it wants to begin building settlements on the planet.
Advantages and disadvantages of Martian concrete:
- On Mars, the concrete could be re-heated until the sulphur melts and the concrete block becomes malleable again, making the material reusable and less of a toll on the planet’s environment
- Has a natural resistance to acid and salt. and can endure very low temperatures
- Martian concrete will soften at a temperature lower than its ignition point
- A Martian habitat would require an interior pressure vessel to maintain a liveable atmosphere
- It does not hold its form well until an outer layer of solidified material develops.