Improving on the Original
Of course, in all these tests, you have to wonder what material scientists are actually using in their experiments. It's just as expensive to bring stuff back from the moon as it is to take it there, so where are they getting all this moon rock? Several teams have created and continue perfecting different simulations of lunar rock to put through the paces.
For example, a 1988 project at the University of North Dakota created an acceptable mixture from lignite coal ash, but every team has its own favorite moon rock substitute. Only a very small number have the cool distinction of doing their tests on the real deal. In 1986, a team created one of the strongest lunarcrete samples with actual moon-originated material by injecting steam made from mixing hydrogen with ilmenite, a lunar rock compound, into their compound at an extremely high temperature.
Though the recipe for lunarcrete varies from lab to lab, its average compressive strength ranges from 39 to 75.7 megapascals (MPa). A megapascal is a unit of measure specific to crushing, and 1 MPa is equivalent to about one tenth of Earth's atmospheric pressure at sea level. Anything more than 50 Mpa is generally a good strength for concrete, while soft sandstone is more in the 5 to 10 Mpa range [source: Ruess et al].
The opposite of compressive strength -- how far you can pull or bend a material before it begins to break -- is called tensile strength. When your foundation cracks, it's likely that the normal pressures associated with expansion and contraction have overcome your concrete's tensile strength. Like concrete, lunarcrete is susceptible to these pressures, so reinforcing tensile strength is important. But Earthling solutions, like adding steel, aren't really viable. Some experts have suggested adding Kevlar to the mix, since it's so much lighter to transport, but the real DIY solution is even more exciting: Create lunar glass from the regolith, and use it to reinforce the lunarcrete the same way we use fiberglass down here.