Lunar soil, as an in-situ resource, holds significant potential for constructing bases and habitats on the Moon. However, such constructions face challenges including limited mechanical strength and extreme temperature fluctuations ranging from -170 degrees C to +133 degrees C between lunar day and night. In this study, we developed a 3D-printed geopolymer derived from lunar regolith simulant with an optimized zig-zag structure, exhibiting exceptional mechanical performance and thermal stability. The designed structure achieved remarkable damage tolerance, with a compressive strength exceeding 12.6 MPa at similar to 80 vol% porosity and a fracture strain of 3.8 %. Finite element method (FEM) simulations revealed that the triangular frame and wavy interlayers enhanced both stiffness and toughness. Additionally, by incorporating strategically placed holes and extending the thermal diffusion path, we significantly improved the thermal insulation of the structure, achieving an ultralow thermal conductivity of 0.24 W/(m K). Furthermore, an iron-free geopolymer coating reduced overheating under sunlight by 51.5 degrees C, underscoring the material's potential for space applications.

The use of geo-synthetics, such as geotextiles, has the potential to enhance the inherent engineering and geotechnical properties of subgrade soils that exhibit poor conditions. The use of geotextiles in pavement construction has many advantages, including enhanced subgrade strength and the ability to construct flexible pavements that are both efficient and cost-effective since it reduces the pavement thickness. In the realm of flexible pavement system development, the significance of subgrade soils and their inherent characteristics, including permeability and strength, is well acknowledged. The study included conducting experiments to investigate the use of geo-polymeric materials like geo-textiles on improving the mechanical properties of the subgrade soils under varying moisture conditions. Geotextiles possess good tensile resistance as it is made up of good polymeric material like polyester, polypropylene and polyethylene. Geotechnical tests including grain size analysis, Atterberg limits, California bearing ratio test, and compaction tests, were conducted. CBR tests and UCS tests were conducted by placing the geotextiles in a singular arrangement at various depths and subjecting them to both soaked and unsoaked conditions to assess the soil's strength. The results demonstrate that the use of geosynthetic reinforcement in the soil effectively enhances the strength of the subgrade across various soil types. The optimal performance of geo-synthetics in relation to their placement inside the CBR mold was found to be at a distance of 1/3 of the mold's height from the top. This placement outperformed the alternative distances of 1/2 and 2/3 of the mold's height.

Geopolymers assume an irreplaceable position in the engineering field on account of their numerous merits, such as durability and high temperature resistance. Nevertheless, geopolymers also demonstrate brittleness. In this study, geotextiles with different layers were added to geopolymer to study its compressive strength and stability. Laboratory materials such as alkali activators, geotextiles and granite residual soil (GRS) were utilized. The samples were characterized via XRD, TG-DTG, SEM-EDS and FT-IR. The results indicate that the toughness of geopolymer is significantly enhanced by adding geotextiles, and the strength increase is most obvious when adding one layer of geotextile: the strength increased from 2.57 Mpa to 3.26 Mpa on the 14th day, an increase of 27%. Additionally, the D-W cycle has a great influence on geotextile polymers. On the 14th day, the average strength of the D-W cyclic sample (1.935 Mpa) was 1.305 Mpa smaller than that of the naturally cured sample (3.24 Mpa), and the strength decreased by 40%. These discoveries offer a novel approach for further promoting the application of geopolymers, especially in the field of foundation reinforcement.

Currently, there are materials from industry that, under certain physical conditions, can contribute to the improvement of soils mechanical properties. Materials such as brick dust (BD) and fly ash (FA) have high SiO2 and Al2O3 contents, which denote pozzolanic activity. In addition, it has been shown that these materials can be activated when combined with lime. This generates internal cementation processes when the particle size is 0.075 mm. Rural roads in Colombia have one of the highest percentages of the entire road infrastructure, and only about 7% are in good condition. Difficult access conditions, soil susceptibility, the financial impossibility of intervening in this entire network and the need to implement circular economy processes, make these materials attractive in terms of stabilization to improve traffic conditions. BD and FA were applied in dosages of 0%, 3%, 6%, 9%, 12% and 24% in finogranular soils (silt and clay) and sandy soils, compaction was evaluated, and a factorial experimental design was carried out to evaluate the influence of the material on the variable unconfined compressive strength (UCS), through an ANOVA analysis. To evaluate the performance of BD and FA, a test track was made on a low traffic volume road in northern Colombia, which had a sandy soil. BD and FA were added at 12% and activated with lime, in 30 m long cells. To establish a comparative pattern, other cells were made in the same geometric conditions with materials that are usually used in this type of application, such as cement. These cells were evaluated over a period of 16 months. Characteristics such as resilient modulus, international roughness index (IRI) and slip resistance coefficient were measured during this period. The results indicate that when these materials are added to finogranular soils (silts and clays), the UCS increases by 150% with respect to the unstabilized soil, while for sandy soils the strength increases from 70% to 125%. During the evaluation period, the BD and the FA were able to increases of over 50% in the resilient modulus with respect to the unstabilized soil. However, the FA showed comparable results with respect to the cement-stabilized cell. In addition, although the sections deteriorated over time, they maintained their roughness index within the admissible ranges indicative of a good serviceability index.

This study investigates the impact of residue soil (RS) powder on the 3D printability of geopolymer composites based on fly ash and ground granulated blast furnace slag. RS is incorporated into the geopolymer mixture, with its inclusion ranging from 0% to 110% of the combined mass of fly ash and finely ground blast furnace slag. Seven groups of geopolymers were designed and tested for their flowability, setting time, rheology, open time, extrudability, shape retention, buildability, and mechanical properties. The results showed that with the increase in RS content, the fluidity of geopolymer mortar decreases, and the setting time increases first and then decreases. The static yield stress, dynamic yield stress, and apparent viscosity of geopolymer mortar increase with the increase in RS content. For an RS content between 10% and 90%, the corresponding fluidity is above 145 mm, and the yield stress is controlled within the range of 2800 Pa, which meets the requirements of extrusion molding. Except for RS-110, geopolymer mortars with other RS contents showed good extrudability and shape retention. The compressive strength of 3D printing samples of geopolymer mortar containing RS has obvious anisotropy.

There is a lack of research on the molecular interactions between clay minerals and geopolymers at the nanoscale, as well as the interfacial mechanism and mechanical behavior of geopolymers, as a highly promising sustainable soft soil reinforcement stabilizer (grouting reinforcement method). In this study, molecular dynamics simulations were used to reveal the interfacial characteristics and the molecular behavior of geopolymer stabilizers and clay minerals. Molecular models of two geopolymers (calcium aluminosilicate hydrate (C-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H)) and two major minerals (montmorillonite and illite) in soft Hangzhou clays were developed. Then, the interfacial characteristics, interaction mechanisms and mechanical behaviors of different geopolymer/clay mineral interface systems were compared. It was found that montmorillonite and illite attract water molecules to aggregate on the mineral surfaces and promote the migration and diffusion of Ca2+ and Na+ at the interfaces. The interfacial interactions of the geopolymer/clay mineral system mainly consisted of electrostatic interactions. Stronger hydrogen bonding interactions occur at the interface of the geopolymer/clay mineral system. The metal cations and the geopolymer stabilizer between the clay mineral layers form a complex ion nest in concert with the aggregated water molecules to stabilize their interfacial interactions. In terms of the mechanical properties, the C-A-S-H stabilizer has a stronger interfacial shear strength. The shear strength of the illite system is stronger than that of the montmorillonite system, but montmorillonite can produce stronger interfacial bonding with the ground polymer stabilizer, and the curing effect is more obvious.

Soil stabilization, crucial for enhancing the stability and engineering properties of soil, has been the subject of extensive research utilizing mechanical and chemical methods. This study delves into the challenges faced in traditional soil subgrade stabilization methods, stemming from factors such as soil erosion, inadequate load-bearing capacity, and susceptibility to environmental conditions. These challenges have prompted the exploration of innovative solutions for road subgrade soil stabilization. Our primary motivation stems from the limitations of conventional techniques and the pressing need to address issues like resource exploitation and environmental pollution. Geopolymers, specifically alkaline-activated materials, have emerged as a promising alternative for soil stabilization. This research investigates the effects of geopolymer blended with rice husk ash (RHA) and fly ash (FA) on various geotechnical properties of natural and admixed black cotton soil. The soil is replaced with admixtures ranging from 0% to 30% of blended geopolymer by weight. The study provides a comprehensive analysis, focusing on quantifiable improvements in soil properties through numerical results. The investigations consistently reveal that the application of geopolymer as a soil stabilizer results in notable improvements in the geotechnical properties like index properties, strength properties, resistance to penetration (CBR), etc., of problematic soil. Comparative analysis with traditional methods underscores the superiority of the proposed geopolymer blend, showcasing its innovation, sustainability, and cost-effectiveness. The findings of this study contribute to the advancement of soil stabilization techniques, specifically in the context of geopolymer applications. For future work, this study suggests an in-depth exploration of geopolymer-stabilized soil's long-term durability and environmental impact. Additionally, further research could focus on optimizing the geopolymer blend ratios for varying soil types and environmental conditions.

Problematic ground conditions constituted by weak or expansive clays are commonly encountered in con-struction projects and require some form of chemical treatment such as lime and cement to re-engineer their performance. However, in the light of the adverse effects of these traditional additives on the climate, alternative eco-friendlier materials are now sourced. In the current study, the viability of calcinated wastepaper sludge ash geopolymer in enhancing the engineering behaviour of a problematic site condition is evaluated. A highly expansive clay (HEC) constituted with a blend of kaolinite and bentonite clays is treated with calcinated wastepaper sludge ash (CPSA) geopolymer. Activation of the precursor is actualised at room temperature using a combination of NaOH and Na2SiO3 at various activator to soil + binder ratios (AL/P), and molarity (M). The mechanical, microstructural, and mineralogical characteristics of the treated clay were investigated through unconfined compressive strength (UCS), swell, water absorption, SEM, and EDX analysis. The performance of the stabilised samples was then compared with the requirements for road subgrade and subbase materials and that of OPC and lime-GGBS treatment. The results showed that CPSA-geopolymer enhanced the engineering properties of the treated clay better than traditional binders (OPC and Iime-GGBS). UCS improvement of 220 % was observed in the CPSA-stabilised soil over that of OPC-treated ones, while the swell potential and water absorption were drastically reduced by over 95 and 97 % respectively after 28-day soaking. The SEM and EDX results showed improved crystallisation of earth-metal-based cementitious flakes (NASH) with increasing CPSA, molarity, and AL/P ratios, which enhanced the inter-particle bonds with simultaneous reduction in porosity. The modified characteristics of the stabilised materials meet the requirements for pavement subgrades. Further, the equivalent carbon emission (CO2-e) from the stabilised materials were also evaluated and compared with that of traditional binders. The results also showed that CPSA-geopolymer had lower CO2-e at higher subgrade strengths than OPC, making it more eco-friendly. Therefore, wastepaper sludge, a common landfill waste from paper recycling is a viable geopolymer precursor that could be utilised in enhancing the engineering properties of subgrade and sub-base materials for road and foundation construction.

In the field of engineering, sustainable solutions that can generate lower environmental impacts, either through material replacement or reuse, are increasingly sought after. In Brazil, in the geotechnical area, there is a demand to find solutions to avoid the disposal of tailings sludge destined for structures, following the recent dam ruptures of Fundao in 2015 and Corrego do Feijao in 2019. One of the recent investments is in the treatment of tailings, generating by-products. To improve the mechanical properties of these by-products, geopolymer utilization has been employed. Geopolymers are products resulting from reactions between aluminosilicate precursors and alkaline activators. The objective of this study is to evaluate the unconfined compressive strength of an iron ore tailings by-product stabilized with a geopolymer that utilizes perlite waste as a precursor and sodium hydroxide as an activator through a two-part alkali-activation process. Two molar concentrations of activators, 2M and 5M, and two sample compositions were evaluated: one with 20% geopolymer and 80% iron ore tailings by-product, and another with 30% and 70%. An increase in unconfined compressive strength was observed with higher concentrations of the activator solution and a greater percentage of geopolymer in material stabilization. Thus, it can be stated that the use of geopolymers in by-product stabilization is promising, but finding the optimal dosage and evaluating other variables such as curing time and temperature is necessary.