Dr. Houssam Toutanji, a professor at the University of Alabama in Huntsville, has recently published an article which deals with a concept of creating concrete structures on the lunar surface without the use of water. Since regular concrete requires water, it is currently unlikely that conventional concrete structures will be built on the moon; however, this inventive idea might hold the key to future lunar settlements.
Traditional concrete comprises a mixture of cement, water, and aggregates. Although recent studies have shown evidence for water in the Moon’s interior, such resources may be more valuable for astronauts’ consumption than for building structures. Therefore, Toutanji’s concept could be of high value for future lunar construction plans.
Toutanji’s article, titled "Unconventional Approach," has been published in the October issue of the Civil Engineering magazine and was written together with Dr. Richard N. Grugel, a geological engineer at NASA's Marshall Space Flight Center. The new research shows that lunar soil could be used as the aggregate, and sulfur as a binding agent for future lunar concrete.
Toutanji, who is also chair of the civil and environmental engineering department at UAHuntsville, has spent years studying the characteristics of cementitious materials. He said that he anticipates concrete to play a major role in constructing facilities on the lunar surface due to the Moon's surface harsh environment. The reason is that survival in such conditions requires solid, durable, materials. For some time now NASA has been searching for resources that are available from the surface of the moon. According to Toutanji, the difficulty of transporting materials from Earth gives a high value for any useable resources found on the Moon.
In his article Toutanji explain some of the advantages of the “waterless concrete,” also known as sulfur concrete. To begin with, it is not a true concrete – at least not 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, and apparently the moon offers several of its basic compounds.
The creation of the waterless concrete requires the melting of sulfur, which in this case acts like a thermoplastic material. Afterwards, the compounds are mixed it with an aggregate. The mixture is then poured, molded, and allowed to harden. Sulfur concrete usually contains 12% to 22% sulfur by mass and 78% to 88% aggregate by mass. Moreover, the sulfur can also contain plasticizers (5 %) and the aggregate can include both coarse and fine particles.
Sulfur is generally expected to melt at about 119 C and stiffen above 148 C; therefore, the sulfur and aggregate must be mixed and heated at a temperature between 130 C and 140 C. Thus, the environment in which sulfur concrete is used must not have a temperature greater than the melting point of sulfur. In addition, fiberglass can be used as a reinforcement of sulfur concrete, in order to improve its tensile and flexural strength.
The advantage of using fiberglass formation on the lunar surface is that it could be produced directly from the lunar soil or from the by-products obtained in extracting such metals as aluminum and titanium. One major material involved in the creation of the waterless concrete is available on the moon – sulfur – making this alternative concrete a favorable option for future lunar construction.