Structural performance of cement paste cylinders cured in microgravity on the ISS: effects of air-entraining agent and simulated microgravity conditions

Abstract As humanity looks to the stars for future colonies, mastering the science of construction in space begins with a deep understanding of how materials perform in extraterrestrial environment. This study pioneers investigations of microgravity effects on cement paste bulk properties. Samples, produced in defined cylindrical shapes on the International Space Station (ISS), allowed for the first-time determination of macroscopic compressive strengths of microgravity samples. A thorough analysis revealed significant impacts on composition, density, and porosity, with compressive strength (− 19%) and Young’s modulus (− 5.5%) lowered due to increased overall porosity (+ 12.3%). Unexpectedly, the addition of an air-entraining agent resulted in lower overall porosity (− 8.7%) and higher compressive strength (+ 18.6%) in microgravity samples as compared to normal gravity (g) on earth. While this effect was consistent across the tests, the underlying cause remains unresolved. Ground-based microgravity simulators like the clinostat and the random positioning machine partially replicated microgravity effects, revealing the challenges of simulating actual microgravity. Achieving homogeneity and preventing large air voids require optimization of the manufacturing-concrete mixing processes, but nevertheless the findings underscore the feasibility of high-quality concrete production in microgravity.