Behavior of Simulated Lunar Cement Mortar in Vacuum Environment

Anorthite rocks found in Hokkaido, Japan have chemical compositions similar to those of lunar anorthite rocks brought back from Highland regions of the Moon. Because of the compositional similarity, Hokkaido anorthite was used in this laboratory study in which simulated lunar cement was made through a high temperature sintering process, rapid quenching, and proper grinding. The needed mortar was prepared by mixing one part of the obtained lunar cement (or Portland cement for reference cubes) and two parts of river sand that met the JIS requirements. The Dry-Mix/Steam-Injection (DMSI) method that was developed solely for the future lunar construction and the conventional wet-mix procedure that was intended to make reference cubes were applied to make series of 40 mm mortar cubes. All test cubes including the wet-mix ones after 28-day curing in a moist room were subjected to compression tests at 1(DMSI), 3(wet-mix), 7, 28, and 180 days(only OPC-DMSI) of moist curing. Measured compressive strengths for wet-mix cubes made with simulated lunar cement were relatively low, only 5.8 N/mm², and those of DMSI cubes were remarkably high, 24.3 N/mm², after 180 days of air curing. Samples of tested cubes at 0, 20, 60, 270, and 330 days of vacuum exposure of 10^–4 torr were tested to determine pore-size distributions and incremental pore as well as cumulative pore-volumes at selected vacuum exposure ages. It concluded that the DMSI cubes showed no imminent pore-size changes but the wet-mix cubes had surprising variations. This paper presents quantitative data on effect of vacuum on simulated lunar cement mortar. This preliminary study program produced useful information that signifies the applicability of concrete to future lunar construction. Nonetheless, a one-year time frame is too short for a vacuum related durability study. We hope to carry out a more comprehensive test program with a minimum of 3-year time frame for the follow-up study.