From clay on the ground to construction on the moon

Building material samples from the University of Delaware spent six months mounted outside of

the International Space Station, where the harsh conditions of low Earth orbit tested their limits.

Some returned with higher measured strength than identical samples stored on Earth.

The findings are a promising sign for the long-term goal of building infrastructure on the moon.

There are no lunar supply yards, and transporting building materials from Earth would be

prohibitively expensive. The solution may lie underfoot, in the form of lunar dust known as

regolith.

“Regolith is essentially a clay-like silicate material,” said Norman Wagner, Unidel Robert L.

Pigford Chair in Chemical Engineering. “It is one of the most abundant materials on both Earth

and the moon, which makes it interesting for construction.”

Wagner's laboratory develops geopolymers, a cement alternative that binds clays into a strong

solid through chemical reactions rather than high-temperature manufacturing. Their goal is to

use regolith with minimal additives to produce construction materials without energy-intensive

processing. The approach could contribute to more sustainable Earth-based construction, too.

To evaluate how geopolymers hold up in space, the UD team sent thin plates made from

commercially available simulated lunar and Martian regolith to the International Space Station

as part of NASA's MISSE-20 mission.

The findings, published in Advances in Space Research, showed the geopolymers did not

deteriorate, and in some cases were stronger after their time in orbit.

Lunar construction materials must not only survive space conditions, they also must be reliably

manufactured on-site. In a separate study in Acta Astronautica, Wagner's team used artificial

intelligence to tackle a practical challenge: not all lunar clays are the same. The researchers

developed a machine learning model that can predict how strong a geopolymer will be based on

the characteristics of the starting regolith and how it is processed.

Complementary work from the Wagner lab offers insight into how geopolymers behave while

being mixed, pumped and shaped before they harden. The researchers identified a key transition point, known as the critical gel point, at which the material shifts from a workable slurry into a solidifying structure. Mixing or shearing before that point did not affect how long the material took to harden or its final strength. This suggests that engineers may have flexibility in how they handle and process lunar construction materials, without compromising quality.

That work appears in a special issue of the Journal of Rheology focused on materials behavior

beyond Earth.

To speak with Wagner about his space expertise, reach out to mediarelations@udel.edu.