Tikalon Blog by Dev Gualtieri

Martian Brickwork

May 29, 2017

Many words have an aura of strangeness to very young children who know the meaning of so few words. As our vocabularies increase, words become less strange, but there is the occasional surprise. While taking an American history course in high school, I read a document containing the strange word, "brickbat." A brickbat, as you would surmise, is a piece of brick used as a weapon. Since our modern world has far better weaponry, the term presently means a highly critical or insulting remark.

Brick is a common building material whose use goes back many millennia. The earliest bricks, which were sun-dried blocks of clay called mudbrick or adobe, have been dated to about 7,500 BC, and they are very durable in dry climates. Fired brick, formed by heating such materials in a kiln, was first manufactured at about 3,000 BC. Primitive brick manufacture involved such processes as having oxen mix the clay by trampling it.

There are various ways of stacking brick to make a wall, as shown by these cross-sections of various types of bricks walls common in 1928.

(Fig. 5 of Ref. 1, redrawn using Inkscape.)[1]

Aside from the notable exceptions of some works of Lucretius (99BC-55BC), Pliny the Elder (23-79), and Vitruvius (c. 75BC-c.15BC), the Romans were more interested in engineering than science.[2] One technical area in which the Romans excelled was civil engineering, which included the use of concrete and brick. I wrote about Roman concrete in a previous article (In Search of... Ancient Concrete, July 1, 2013).

Roman brick was originally mudbrick, but development of the fired brick technology of the Greeks started in the Roman Empire at the time of Augustus, and it became a dominant technology in the 1st century. As the Roman Empire expanded, so did the knowledge of making bricks.

Today, a brick is usually made from a mixture of the ingredients listed below, pressed in an hydraulic press, and fired at about 900–1000 °C. A house brick in the United States has a standard size of 7-5/8" x 3-5/8" x 2-1/4" (194 mm x 92 mm x 57 mm). After firing, the material is an hydrated aluminosilicate.[3]

Silica, 50-60 wt-%
Alumina, 20-30 wt-%
Lime, 2-5 wt-%
Iron oxide, ≤7 wt-%
Magnesia, <1 wt-%

A brick wall at the National Shrine of the North American Martyrs, Auriesville, New York

While working at the University of Pittsburgh, I discovered that most Pittsburgh houses are built of brick. This is a reaction to a devastating fire in the city in 1845 that destroyed more than a thousand wooden buildings.

Brick walls are often aesthetic, as shown by this photo of a portion of a brick wall at the National Shrine of the North American Martyrs, Auriesville, New York.

(Photo by the author.)

Mars is an inhospitable place to live. In my novel, The Alchemists of Mars, a band of humans survived on Mars for hundreds of years by living underground. Since Mars has been devoid of water in its recent history, there's no abundance of Martian caves as there is on Earth, so these humans needed to dig their own cave. Fortunately, they were assisted in this by their alchemical arts.

A team of engineers and materials scientists at the University of California-San Diego (La Jolla, California) has suggested that humans might build their own Martian caves in the form of brick houses. Their experiments of making bricks by the simple compaction of a simulated Martian regolith (soil) has just been published as an open access article in Scientific Reports.[4-5]

Much of the characteristically red Martian soil consists of nanoparticulate iron oxides and iron oxyhydroxides.[4] A widely used Martian soil simulant, Johnson Space Center Mars-1a, is composed of a basaltic body coated with these oxides.[6] The major components of Martian surface soil and the Mars-1a simulant are shown in the table.

Component	Mars regolith (Wt-%)	Mars-1a (Wt-%)
SiO₂	45.41	43.48
Fe₂O₃ & FeO	16.73	16.08
MgO	8.35	4.22
CaO	6.37	6.05

When you're dealing with a very long and expensive supply chain, it's important to make best use of the materials at hand. The San Diego approach to making Martian bricks is important, since it avoids the addition of other materials, and it relies on compaction, alone, without firing. Previous approaches required the use of binder agents transported from Earth, and firing in nuclear-powered brick kilns.[4-5] Mars does contain some organic compounds, but complex chemistry would be need to transform these into binding polymers.[5]

Many discoveries happen by accident. The San Diego engineers started examining how small a quantity of binding polymer might be needed to make Martian bricks, and they discovered that no binding polymer was needed.[5] While basaltic particles will not bond together without heating, the surface oxides of the basaltic core nanoparticles form strong bonds.[4]

An important step was enclosure of the material in a flexible container, a rubber tube, for compaction. This allowed movement and reorientation of the individual nanoparticle grains. Another was compaction at a high enough pressure, equivalent to a 10 pound weight dropped from one meter (on Mars, the drop would need to be somewhat larger).[4-5]

Photographs of bricks made from simulated Martian soil

Photographs of brick processing from simulated Martian soil. Left, a brick made of Martian soil simulant, compacted under pressure without any additional ingredients or firing. Middle, a brick after strength testing. Right, soil, compacted in a cylindrical, flexible rubber tube before being cut into bricks.(Left, center, and right images by the UC San Diego Jacobs School of Engineering.)

Small soil cylinders, about an inch tall, are produced by the laboratory-scale process, and these were cut into brick shapes. Microscopic examination showed that the iron oxide particles had clean, flat facets that easily bonded to each another under compaction.[5] The strength of the brick, in the range 30-50 MPa, was found to exceed that of steel-reinforced concrete.[4-5] Martian colonists need not form bricks, since structures can be built additively by putting down a layer of soil, compacting it, then repeating the process.[5] The gas permeability of compacted samples was of the order of 10^-16 m², which is near the value for solid rock.[4]

Flexural strength of a bricks made from simulated Martial soil as a function of impact energy. Two different particle sizes were used, with smaller particles giving higher strength.

(Image of fig. 3-A of ref. 4, licensed under the Creative Commons Attribution 4.0 International license.)[4]

The next task is to increase the size of the bricks.[5] This research was funded by NASA.[4]

Martian Brickwork

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