Mars is increasingly considered for colonization by virtue of its Earth-like conditions and potential to harbor life. Responding to challenges of the Martian environment and the complexity of transporting resources from Earth, this study develops a novel geopolymer-based high-performance Martian concrete (HPMC) using Martian soil simulant. The optimal simulant addition, ranging from 30% to 70% of the total mass of the binders, was explored to optimize both the performance of HPMC and its cost-effectiveness. Additionally, the effects of temperature (-20 degrees C-40 degrees C) and atmospheric (ambient and carbonated) curing conditions, as well as steel fibre addition, were investigated on its long-term compressive and microstructural performance. Optimal results showed that HPMC with 50% regolith simulant achieved the best 7-day compressive strength (62.8 MPa) and the remarkable efficiency improvement, a result of ideal chemical ratios and effective geopolymerization reaction. Under various temperature conditions, sub-zero temperatures (-20 degrees C and 0 degrees C) diminished strength due to reduced aluminosilicate dissolution and gel formation. In contrast, specimens cured at 40 degrees C and 20 degrees C, respectively, showed superior early and long-term strengths, with the 40 degrees C potential for moisture loss related shrinkage cracking and reduced geopolymerization. Regarding the atmospheric environment, carbonation curing and steel fibre addition both improved the matrix compactness and compressive strength, with carbon-cured fibre-reinforced HPMC achieving 98.3 MPa after 60 days. However, long-term exposure to high levels of CO2 eventually reduced the fibres' toughening effect and caused visible damages on steel fibres.

Colonizing other planets, like Mars, marks a significant milestone in the pursuit of a multi-planetary existence. Millions of people would settle on Mars in self-sufficient bases. Colonizing Mars is a long-term mission that demands self-sufficient, secure habitats and comprehensive planning. Importing structures, such as inflatable structures, from Earth is cost-prohibitive, making the utilization of in-situ resources and onsite construction the most viable approach for preparing the required buildings. Studies have shown that it is possible to produce and craft several kinds of binders and concretes with appropriate mechanical behavior using Martian soil composition; however, determining the optimal option for onsite construction remains a challenge. This study investigates available cement/concrete options for onsite construction on Mars from a structural engineering perspective, taking into account the available resources and technologies. In this regard, the observations and data provided by Martian landers, rovers, orbiters and methods such as Viking-1 & 2, Pathfinder, Spirit, Opportunity, Curiosity, Mars Express, Ultraviolet-visible/Near-infrared reflectivity spectra and Alpha particle X-ray spectrometer were used to obtain a comprehensive and detailed investigation. Eleven types of Martian cement/ concrete based on the in-situ resources, soil composition, and available technologies were compared based on the criteria and indices defined in accordance with the structural engineering point of view to select the best practical option for onsite construction. These criteria encompass factors such as mechanical behavior, Martian structural loads, raw material accessibility, available sources, energy required for production, water requirement, curing and hardening time, possibility of using 3D printers, byproduct usefulness, conditions required for hardening and curing, importation requirements from Earth, production complexity, long-term durability and behavior under galactic cosmic rays (GCRs) and solar energetic particles (SEPs). The pros and cons of each cement/concrete option are thoroughly assessed, considering the harsh conditions on Mars. Additionally, the study highlights extra considerations that are crucial for onsite construction on Mars. To determine the best practical option for onsite construction and sustainable colonization, the proposed cements/concretes were compared using multi-scale spider/radar diagrams and a quantitative point of view. This perspective was enabled by assigning weights to each criterion through expert consultation, experimental data, and literature review, ensuring that the diagrams accurately reflect the features of each concrete mix. This comprehensive investigation aims to provide valuable insights into selecting the most suitable cement/concrete for onsite construction on Mars, considering the structural engineering perspective and the long-term goal of sustainable colonization.