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Details of Grant 

EPSRC Reference: EP/X018504/1
Title: Martian Rammed Earth
Principal Investigator: Hughes, Dr PN
Other Investigators:
Lloret-Cabot, Dr M Knappett, Professor JA
Researcher Co-Investigators:
Project Partners:
UK Space Agency
Department: Engineering
Organisation: Durham, University of
Scheme: Standard Research - NR1
Starts: 01 November 2022 Ends: 31 October 2024 Value (£): 199,354
EPSRC Research Topic Classifications:
Ground Engineering Materials testing & eng.
EPSRC Industrial Sector Classifications:
Construction
Related Grants:
Panel History:
Panel DatePanel NameOutcome
21 Jun 2022 New Horizons 2021 Full Proposal Panel Announced
23 Jun 2022 New Horizons Civil Engineering Panel June 2022 Announced
Summary on Grant Application Form
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.
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