Lunar Concrete Made with the Dry-Mix/Steam-Injection Method

Abstract

To cast concrete on the Moon requires a new procedure to overcome the ill-suited vacuum condition. The proposed new procedure is to mix cement and aggregate in a dry state and expose the mixture to steam in a confined chamber to enforce hydration at elevated temperatures and pressures. A test program was carried out at the National Chiao Tung University in 1993 to verify the concept of the proposed Dry-Mix/Steam-Injection (DMSI) procedure. The hydration mechanism of a dry cement mixture with high temperature steam differs from that of the conventional wet mix procedure in two ways. First, a rapid transfer of thermal energy from steam causes the cement particles to raise their activation energy to expedite a complete hydration. Second, steam particles are very small, in the order of 3 Angtron in diameter, capable of penetrating micron pores inhibited in cement particles. Concrete thus made developed a high strength of 700 kgf/cm2 (10,000 psi) after 18 hours of steaming at 180 C. It is approximately 2.5 times that of companion concrete made with the conventional wet-mix procedure after 28 days of moist curing. Another test series revealed that the DMSI method required only 50% of the cement needed in making concrete of an equivalent strength of 560 to 630 kgf/cm2 (8000 to 9000 psi) through the wet-mix procedure.