Effect of the freezing temperature and near-vacuum air pressure of Mars on the mechanical properties and microstructure of hydrogel-based concrete (HBC)

Hydrogel has been used as aggregate binder to form hydrogel-based concrete (HBC). HBC can maximize the in-situ resource utilization (ISRU) at a construction site with only water and natural aggregates, e.g., Mars. In this study, the curing effect of combined extremely low temperature (-55 C) and near-vacuum air pressure (10 Pa, or 0.01% atm), which mimic the Martian surface environment, on the mechanical properties of HBC is investigated for the first time. HBC cubes were made with a wide range of sol-to-aggregate ratios (0.05 to 0.4). Compressive tests were conducted with the cubes; microstructural evolution of the inter-aggregate gel joint was examined. The experimental results indicate that the elastic modulus and compressive strength of all HBCs first increase until the increasing s/a ratio reaches a critical value and decreases afterward, despite the different curing conditions; the frozen and freeze-dried HBCs have lower mechanical strength than the air-dried ones. The different mechanical properties, induced either by the s/a ratio or the curing conditions, are mainly attributed to the evolution of gel microstructure instead of the change of gel property. A finite element model of a four-story beacon under typical loadings on Mars surface was created to study the feasibility of using frozen and freeze-dried HBCs as the constituent material. The results show that they can provide adequate mechanical strength for this niche application.(c) 2022 Elsevier Ltd. All rights reserved.