The utilization of in-situ lunar resources through the additive manufacturing of lunar regolith (LR) has attracted considerable interest. Sintering of LR is considered a promising method for lunar construction due to its high utilization rate and excellent service stability. However, numerous studies have been carried out on Apollo series LRs with similar chemical compositions in air or inert gas atmospheres. The effects of the lunar ultra-high vacuum conditions and the complex chemical composition of LRs on the sintering process require extensive investigation. In this study, a self-developed Chang'E-5 lunar regolith simulant (LRS) with a high-Fe content was used as the only raw material to investigate its potential applicability for future lunar construction in vacuum environment. The effects of sintering temperature on the microstructure, linear shrinkage, bulk density, weight loss ratio, and mechanical and thermal expansion properties were investigated. The results show that the linear shrinkage and weight loss ratio increase with increasing sintering temperature. However, the bulk density and unconfined compressive strength (USC) initially increase and then decrease, with the sample sintered at 1075 degrees C giving the highest bulk density of 2.10 +/- 0.03 g/cm3 and a USC of 31.19 +/- 1.96 MPa. This is attributed to the transformation of the sample sintered at 1090 degrees C into a semi-porous material with many cracks. Furthermore, the mechanism of pore and crack formation was revealed. The coefficient of thermal expansion (CET) of the sintered samples is approximately 7x10-6 degrees C 1, which maintains a good service stability after cyclic temperature stress from room temperature up to 200 degrees C. Both the USC and CET of the sample sintered at 1075 degrees C are superior to those of common terrestrial concrete materials. This indicates that the vacuum sintering process appears feasible for the production of building materials with sufficient mechanical strength and thermal durability for lunar base construction.

The construction of extraterrestrial bases has become a new goal in the active exploration of deep space. Among the construction techniques, in situ resource-based construction is one of the most promising because of its good sustainability and acceptable economic cost, triggering the development of various types of extraterrestrial construction materials. A comprehensive survey and comparison of materials from the perspective of performance was conducted to provide suggestions for material selection and optimization. Thirteen types of typical construction materials are discussed in terms of their reliability and applicability in extreme extraterrestrial environment. Mechanical, thermal and optical, and radiation-shielding properties are considered. The influencing factors and optimization methods for these properties are analyzed. From the perspective of material properties, the existing challenges lie in the comprehensive, long-term, and real characterization of regolith-based construction materials. Correspondingly, the suggested future directions include the application of high-throughput characterization methods, accelerated durability tests, and conducting extraterrestrial experiments. (c) 2024 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The present work investigates the feasibility of producing boards, with unconventional materials, namely hazelnut shells as a high-mass bio-aggregate and a sodium silicate solution as a no-toxic adhesive, and discusses possible applications based on an extensive characterization. The aim is to define a feasible reuse of a largely produced agro-industrial by-product to reduce the high environmental impact caused by both the construction and the agriculture sectors, by proposing a building composite that improves indoor comfort. The presented combination of aggregate-adhesive generated a product with characteristics interesting to explore. The thermal conductivity is moderated, and the composite achieved values of sigma max = 0.39 N/mm2 for flexural strength and sigma max = 2.1 N/mm2 for compressive strength, but it showed high sorption capacity with a moisture buffering value of about 3.45 g/(m2 %RH), and a peak of sound absorption between 700 and 900 Hz. Therefore, the boards' most promising performance parameters seem to be their high hygroscopicity and acoustic absorption behaviour, namely in the frequency range of the human voice. Hence, the proposed composite could improve indoor comfort if applied as an internal coating board.

High-latitude permafrost, including hydrate-bearing frozen ground, changes its properties in response to natural climate change and to impacts from petroleum production. Of special interest is the behavior of thermal conductivity, one of the key parameters that control the thermal processes in permafrost containing gas hydrate accumulations. Thermal conductivity variations under pressure and temperature changes were studied in the laboratory through physical modeling using sand sampled from gas-bearing permafrost of the Yamal Peninsula (northern West Siberia, Russia). When gas pressure drops to below equilibrium at a constant negative temperature (about -6(degrees)C), the thermal conductivity of the samples first becomes a few percent to 10% lower as a result of cracking and then increases as pore gas hydrate dissociates and converts to water and then to ice. The range of thermal conductivity variations has several controls: pore gas pressure, hydrate saturation, rate of hydrate dissociation, and amount of additionally formed pore ice. In general, hydrate dissociation can cause up to 20% thermal conductivity decrease in frozen hydrate-bearing sand. As the samples are heated to positive temperatures, their thermal conductivity decreases by a magnitude depending on residual contents of pore gas hydrate and ice: the decrease reaches similar to 30% at 20-40% hydrate saturation. The thermal conductivity decrease in hydrate-free saline frozen sand is proportional to the salinity and can become similar to 40% lower at a salinity of 0.14%. The behavior of thermal conductivity in frozen hydrate-bearing sediments under a pressure drop below the equilibrium and a temperature increase to above 0 C-degrees is explained in a model of pore space changes based on the experimental results.