Concreting on moon…Waterless Concrete!
NASA plans to launch manned spacecraft to moon in 2020; but it hopes not just to land on the moon but also to establish longer-term bases for astronauts, and to accomplish this the astronauts will need to be able to build structures using resources that are readily available on the lunar surface. The structures will need to be able to withstand the harsh lunar environment, and for this reason concrete appears to be a suitable building material. Traditional concrete comprises a binder—cement and water—mixed with aggregates, but water will presumably be unavailable on the moon.
Dr. Houssam A. Toutanji, F.ASCE, a professor at The University of Alabama in Huntsville & Richard N. Grugel, Ph.D., a geological engineer at the National Aeronautics and Space Administration’s Marshall Space Flight Center, in Huntsville, Alabamal have published an article (Unconventional Approach. Civil Engineering, October’ 2008) thatdemonstrates a concept of creating concrete structures on the lunar surface without the use of water.
NASA is searching for a means to use resources that are available from the surface of the moon, according to Toutanji. “The difficulty of transporting materials from Earth will place a premium on resourcefulness and ingenuity,” he said. He anticipates concrete to play a major role in constructing facilities on the lunar surface to survive the harsh environment on the Moon’s surface.
Sam Toutanji says that raw materials needed to manufacture concrete on the moon exist in abundance. As a matter of fact, he said concrete produced on the moon has a good chance of being stronger than concrete made on Earth.
He concocted a number of “recipes” and formed small strips of lunar concrete. He then subjected those samples to various types of tests, such as heat, compression and tension.
|Dr. Toutanji’s research so far shows a concrete that is 45 percent stronger. His experiments reveal that concrete produced from lunar soil could withstand pressure of 5,800 pounds per square inch, compared with 4,000 psi for normal concrete on Earth.
The fine, powdery nature of lunar soil actually makes it a good ingredient for concrete because it would create a substance that would have less air gapswithin the cementitious material, according to Toutanji. “The finer the material, the more homogeneous the material will be, and homogeneity usually provides more strength.”
While the lunar soil provides most of the raw materials needed to make concrete, a binding agent is required. On Earth, cement and water are used as that binding agent. Obviously, water is not as plentiful on the moon.” The idea that water exists on the moon is open to discussion. Even if we can find water, it will be such a precious commodity; it will be more valuable for use in other applications.”
In recent months, Toutanji’s research has pointed him in a different direction for a binding agent. It took four years, but he has produced a breakthrough that would allow astronauts to produce concrete without water. ”
“We began looking at the approach of making concrete without water,” he said. “We used the Dry-Mix/Steam-Injected method to produce concrete. We found that this method offers advantages, such as shorter hydration time, higher strength, and less cement and water consumption.” Then, he began experimenting with sulfur to bind the simulant lunar dust together to form the concrete. “We used only sulfur and simulant lunar soil in concrete. We have known that sulfur is useful as a binding material and sulfur cement concrete has been used on Earth in a number of applications.” .
Waterless concrete, also known as sulfur concrete, is not a true concrete in the traditional sense because very little in the way of a chemical reaction occurs between the components.
However, this well-established, albeit expensive, building material can resist corrosive environments in highly acidic or salty areas. To create it, one melts sulfur, which in this case acts like a thermoplastic material, and mixes it with an aggregate. The mixture is then poured, molded, and allowed to harden. Sulfur concrete usually contains 12 to 22 percent sulfur by mass and 78 to 88 percent aggregate by mass. The proportion of sulfur to aggregate is very important in determining the right mix with the best mechanical properties. The sulfur can also contain plasticizers (5 percent), and the aggregate can include coarse and fine particles
He said sulfur is found in abundance on the moon’s surface. “The sulfur content of the lunar regolith is mainly controlled by troilite (FeS), and extracting sulfur from the lunar soil is possible using a series of chemical processes.” Thus, making the prospects of constructing permanent structures on the moon proves to be plausible.
Fiberglass can be used as a reinforcement of sulfur concrete to improve its tensile and flexural strength. Fiberglass formation on the lunar surface is feasible because the material could be produced directly from the lunar soil or from the by-products obtained in extracting such metals as aluminum and titanium.The addition of silica appears to increase the compressive strength of sulfur concrete. However, the silica sulfur concrete seemed to exhibit a more brittle failure
However, Toutanji is quick to point out that many questions remain. “Nothing is going to be simple on the moon. Questions remain about the extreme ambient temperature conditions, cosmic radiation, micrometeorites, as well as simple issues, such as how would a concrete structure be reinforced and framed“.
At the same time, scientists already knew that producing concrete in a microgravity environment does not harm the strength of the concrete. Actually, a 1994 University of Alabama in Huntsville experiment aboard the space shuttle Endeavor showed that microgravity has the opposite effect. The scientists found that a lack of gravity produced fewer voids in the concrete and the material was just as strong. “The combination of low gravity and fine lunar dust could result in a strong concrete.”