This study explores the development of a novel construction material, Hydrogel-based concrete (HBC), specifically designed for Martian environments. HBC is a composite material formed by mixing flowable hydrosol with inert aggregates, offering low energy consumption and minimal shipped ingredients. A variant of Bio-HBC, known as living building material (LBM), incorporates genetically modified yeast cells (Saccharomyces cerevisiae) to produce recombinant SpyTag/SpyCatcher pairs and collagens, which form bio-hydrogel with strong cohesive properties. The study uses the addition of a small portion of engineered yeast to the HBC yields bricks with higher mechanical properties when cured under harsh environments. The bio-HBC has great potential to be adopted with unique attributes such as self-repair, stimuli-responsiveness, and environmental adaptivity.

The study also investigates binder jetting, a low-energy-consuming additive manufacturing process, as a potential method for automatically constructing structures using Bio-HBC. We developed an environmental chamber capable of mimicking Martian conditions, including temperature and air pressure, to test the material's printing compatibility and mechanical performance under extreme environments. The experiments focused on understanding and characterizing binder-powder interaction, determining suitable printing process parameters, and controlling depressurization for successful binder jetting under Martian conditions. The findings demonstrate that Bio-HBC exhibits improved mechanical properties when cured under harsh environments compared to traditional HBC. Additionally, the use of genetically modified yeast cells promotes adhesion and prevents the formation of porous joint structures during freezing.

Reactive magnesium oxide (MgO) cements (RMC) have emerged as one of the promising sustainable alternatives to ordinary Portland cement (OPC) owing to their lower production temperature (700-1000 °C) and reduced CO₂ emissions [1]. Further, the permanent CO₂ sequestration during the strength development of RMC significantly decreases the net CO₂ emissions, making RMC a leading candidate for carbon-neutral/negative construction material. RMC is primarily obtained by calcining naturally occurring but geographically limited magnesite deposits. Therefore, as an alternative route, RMC is also synthesized by calcination of brucite (Mg(OH)₂) recovered from concentrated brine resources (viz. desalination waste) or seawater using chemical processes. This alternative route for RMC production also addresses the challenges related to magnesite availability and management of the byproducts of the desalination process. It has been shown that the synthesized brucite could be directly carbonated for rapid strength gain and utilization as a construction material, also reducing the CO₂ emissions due to the elimination of calcination requirement [1]. However, several challenges are associated with the utilization of brucite, such as high-water consumption, optimization of carbonation conditions, reduced porosity for maximized strength gain, effect of alkali agents on the performance of the synthesized brucite, etc. This study investigated the above-mentioned factors and their impact on the overall performance of brucite for construction applications. The results demonstrated that the different factors affected the type and content of the carbonation phases formed, which in turn, affected the overall compressive strength. The results also indicated that optimization of the synthesis conditions can enhance the compressive strength and CO₂ absorption capacity of brucite.

References:

[1] I. Singh, R. Hay, K. Celik, Recovery and direct carbonation of brucite from desalination reject brine for use as a construction material, Cem. Concr. Res. 152 (2022), 106673.

As urbanization and infrastructure development drive the demand for concrete, natural resources, especially river sand, face increasing pressure. On the other hand, desert sand is abundant but remains underutilized due to its narrow particle size distribution and high specific surface area, which require higher cement content to bind its grains. This study aims to harness desert sand in mortars by using it with belite calcium sulfoaluminate cement (BCSA). The slightly expansive nature of BCSA cement allows for minimal usage while effectively binding the sand particles. In this work, naturally available dune sand, vast deposits of which are available in the United Arab Emirates (UAE) and the broader Middle East and North Africa (MENA) region, were utilized with BCSA cement. The results show that the complete replacement of standard sand with desert sand is feasible when a small quantity of superplasticizer (1% by mass of binder) is used in the mixture. Since BCSA cement is known for its rapid setting ability, the effect of desert sand on the setting time of the mixtures and compressive strengths at different ages (from 1 hour to 28 days) was also investigated. The results indicate that the compressive strength of desert sand mortars (~50 MPa) is comparable to those made from standard sand at the age of 28 days. The results are promising from an environmental perspective since the production temperature of BCSA is lower compared to ordinary Portland cement (OPC) thus reducing the carbon footprint. Using desert sand also reduces reliance on river sand, thereby promoting sustainable construction practices.