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This study investigated the possibility of using volcanic ash and metakaolin (MK) to prepare road grouting materials. The effects of different contents of MK and water glass(WG) on the mechanical properties, setting time and rheological properties of the materials were investigated separately. The materials science testing methods were also used to observe the reaction mechanism of the geopolymer products. The test results showed that the compressive strength increased with the content of MK and SS. The average flow curve of geopolymer grouts fitted the Bingham model. The multilayer lamellar microstructure of MK increases the rheological parameters of the pastes. While the WG suspends VA and MK particles, which reduces the rheological parameters of the pastes. It can be concluded from the results of microscopic experiments that the MK reduces side reactions as well as sodium by-products, while WG produces more silica-aluminate filling the voids which enhance the compressive strength. [ABSTRACT FROM AUTHOR]

Using the Moon's natural resources to build infrastructure is the first step toward lunar colonization. Lunar regolith, rich in aluminosilicate, has the potential to prepare geopolymer for construction. In this paper, carbon nanofibers (CNFs) were added to geopolymers based on lunar regolith simulant, aiming at reinforcing mechanical and microstructural properties. A ball-milling method of CNF dispersion into the lunar regolith simulant was evaluated. The mechanical properties of the resulting geopolymer nanocomposites was investigated. X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, and mercury intrusion porosimetry were used to characterize the microstructural properties. The results indicated that the mechanical properties were improved by CNFs and that the optimal content was 0.3% by weight. Also, flexural strength, Young's modulus, flexural toughness, peak displacement, and compressive strength were reinforced by 34.8%, 7.5%, 83.9%, 21.4%, and 13.1%, respectively. Microstructural results suggested that the CNFs acted as nucleation, fillers, and bridges in the nanocomposites, leading to lower porosity, higher energy requirement for failure, and higher mechanical properties, which are considerable for lunar-based construction. [ABSTRACT FROM AUTHOR]

Volcanic ash has several negative impacts on the environment and can be used in massive to synthesize geopolymers, which are considered quasi-brittle. Carbon nanofibers (CNFs) can reinforce the geopolymers, and the dispersion of CNFs directly determines the reinforcement effect. However, the dispersion of CNFs in alkali solutions is challenging. In this paper, the effect of surfactant type, dosage, and ultrasonic time on CNFs dispersion in aqueous and alkali solutions was investigated by the quantitive method of microscopic image processing to determine the preferred dispersion scheme. Zeta potential tests and visual observation were used to analyze the mechanism and stability. Based on this, volcanic ash-based geopolymer nanocomposites with 0.1 wt% contents of CNFs were synthesized. The mechanical properties were tested, and the microstructure was characterized using Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy and Mercury Intrusion Porosimetry. The results showed that methylcellulose (MC), polycarboxylate superplasticizer (PC), and polyvinylpyrrolidone (PVP) could disperse CNFs in aqueous, but evident aggregations can be observed in the alkali solution. PC performed better than MC and PVP in alkali solutions, with 4.83% aggregation area of the whole image, 86% of 0–100 μm2 aggregations, and an average aggregation area of 87 μm2, beneficial from the comb-like structures. Dispersed CNFs can improve the 28-d flexural and compressive strength of the resulting geopolymer nanocomposite by 23% and 16%, respectively, and refine the pore structure through filling, bridging, and nucleation effects, decreasing the average pore size and porosity by 33% and 15%. This paper will contribute to the resourceful use of volcanic ash to reduce pollution and the higher reinforcement of CNFs in alkali-activated geopolymers. [ABSTRACT FROM AUTHOR]

• Geopolymer can be synthesis using lunar in-situ high temperature. • Time-varying curing temperature influences the strength development. • Lunar extreme temperature causes deterioration in the mechanical properties. • Zeolitic phase materials are products of geopolymerization reaction. Lunar base construction is of great importance for deep space exploration, and the establishment of lunar pavements for the movement of machinery and transportation of materials is essential to improve construction efficiency. Lunar regolith as an in-situ resource has been demonstrated to be used as raw materials to prepare geopolymers for lunar pavements. In this paper, geopolymers based on lunar regolith simulant with different concentrations of alkali activator were synthesized using the natural high-temperature of the lunar surface. Then, the durability of the resulting geopolymer under lunar high and cryogenic temperature was investigated. The flexural and compressive strength was tested, and the microstructure was characterized using Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS), 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (29Si MAS-NMR), and Mercury Intrusion Porosimetry (MIP). The results of the curing section showed that the geopolymer with 8 mol/L sodium hydroxide (NaOH) generated high strength and dense structure, and the period of 420 h–492 h of a lunar day corresponding to a temperature variation from 84.5 °C to 33.5 °C in 72 h was suitable for preparation, with 5.7 MPa and 31.2 MPa 72-h flexural and compressive strength. Three test points were selected on the lunar 30° latitude temperature curve, corresponding to before and after the cryogenic attack, and after high temperature again to investigate the durability of the geopolymer, and the degradation was found noticeable. The flexural strength decreased about 49% and 70%, and the compressive strength decreased about 15% and 18% after the cryogenic temperature and high temperature again, respectively. Microscopic observations revealed that the geopolymer structure was significantly granulated with obvious cracks and increased porosity. In addition, the formation of the zeolitic phase was unexpectedly found, leading to interfacial cracks and mechanical strength reduction of the geopolymer. This paper will be beneficial to explore the evolution of properties of lunar pavement construction materials in the lunar environment. [ABSTRACT FROM AUTHOR]

The construction of a lunar base and habitation on the moon has always been of great significance to utilizing lunar resources and deep space exploration. In this paper, a new type of lunar regolith simulant denoted as BH-2 of similar compositions and particle size distribution with real one was developed and used for geopolymer synthesis under simulated lunar surface temperature and vacuum conditions. The geopolymer products were characterized by compressive strength test, Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope coupled, and 29Si magic angle spinning-nuclear magnetic resonance (29Si MAS-NMR). The results showed that BH-2 lunar regolith simulant could be used to synthesize geopolymer. And the 72-h compressive strength of the geopolymer cured at the temperature of group C, corresponding to the 324–384 h of one lunar day, could reach 38.2 MPa, which was advantageous in the early stages of lunar construction because no additional curing equipment is required. The pores originated from lunar regolith simulant and caused by incomplete geopolymerization resulted in decreased compressive strength of the resulting geopolymer. Vacuum conditions on the moon favored the preparation of lunar geopolymers due to the lack of carbon dioxide weakening the efflorescence effect. This study benefits to lunar base construction with in-situ resource. • A new lunar regolith simulant of similar particle size with real one. • Geopolymer can be cured under lunar natural surface temperature. • Vacuum conditions benefit to the preparation of lunar geopolymers. • The optimum time to cure geopolymer on the moon was found. [ABSTRACT FROM AUTHOR]

Geopolymer has been applied in road engineering as an environmentally friendly material. This study prepared geopolymer road grouting pastes in different mixture ratios of volcanic ash (VA) and metakaolin (MK). The mechanical properties, setting time, bleeding and expansion ratio, fluidity and expansion ratio, time-dependent rheological analysis were systematically evaluated. Finally, the microscopic experiments, including X-Ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy with Energy Dispersive Spectrometer (SEM-EDS), were conducted to investigate the mechanism of geopolymerization based on VA and MK. The results showed that the mechanical strength increased with the content of MK. The flow curve of all pastes fitted the Bingham model. With the increase of MK content, the yield stress and plastic viscosity coefficient increased, which is because the stacked multilayer gullies microstructure aggravated the internal friction of paste particles, which led to decreased expansibility and pumpability. When the mass ratio of VA/MK was 1:0.33, the paste achieved the balance of mechanical strength and rheological properties with superior water retention and deformation resistance. The microscopic experiments showed that MK's mechanism enhanced the mechanical strength of geopolymer due to its high content of amorphous phases, smaller average particle size, and rich content of Al element. The SEM-EDS indicated that the MK improved the mechanical strength also by the improvement of nucleation effect. VA and MK complement each other in mechanical strength development under room temperature and fluidity, which are expected to be an alternative for cement as an eco-friendly road grouting material. [ABSTRACT FROM AUTHOR]