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Contemporary construction faces the need to reduce its negative impact on the environment, prompting designers, investors, and contractors to seek more sustainable materials and technologies. One area of dynamic development is the use of natural fibers as an alternative to conventional, often synthetic, building components. Plant- and animal-based fibers, such as hemp, flax, jute, straw, bamboo, and sheep’s wool, are characterized by low energy consumption in production, renewability, and biodegradability. Their use is in line with the concept of a circular economy and reduces the carbon footprint of buildings. Natural fibers offer a number of beneficial physical and functional properties, including good thermal and acoustic insulation parameters, as well as hygroscopicity, which allows for the regulation of indoor humidity, improving air quality and comfort of use. In recent years, there has also been a renaissance of traditional building techniques, such as straw construction, often combined with modern engineering standards. Their potential is particularly recognized in green and energy-efficient construction. The article provides an overview of the types of natural fibers available for use in construction and analyzes their technical, environmental, and economic properties. It also draws attention to current regulations, standards, and certifications (e.g., LEED, BREEAM) that promote the popularization of these solutions. In light of the analyzed data, the role of natural fibers as a viable alternative supporting the transformation of the construction sector towards sustainable development is considered.

This paper presents the development and characteristics of geopolymer foams modified with paraffin-based phase change materials (PCMs) encapsulated in diatomite. The aim was to increase both the thermal insulation and heat storage capacity of the foams while maintaining sufficient mechanical strength for construction applications. Eleven variants of composites with different PCM fractions (5–10% by mass) and grain sizes (<1.6 mm to >2.5 mm) were synthesized and tested. The inclusion of PCM encapsulated in diatomite modified the porous structure: the total porosity increased from 6.6% in the reference sample to 19.6% for the 1.6–1.8 mm_10% wt. variant, with pore diameters ranging from ~4 to 280 µm. Thermal conductivity (λ) ranged between 0.090–0.129 W/m·K, with the lowest values observed for composites 2.0–2.5 mm_5–10% wt. (≈0.090–0.091 W/m·K), which also showed high thermal resistance (R ≈ 0.287–0.289 m2·K/W). The specific heat (Cp) increased from 1.28 kJ/kg·K (reference value) to a maximum value of 1.87 kJ/kg·K for the 2.0–2.5 mm_10% mass variant, confirming the effective energy storage capacity of PCM-modified foams. Mechanical tests showed compressive strength values in the range of 0.7–3.1 MPa. The best structural performance was obtained for the 1.6–1.8 mm_10% wt. variant (3.1 MPa), albeit with a higher λ (≈0.129 W/m·K), illustrating the classic trade-off between porosity-based insulation and mechanical strength. SEM microstructural analysis and mercury porosimetry confirmed the presence of mesopores, which determine both thermal and mechanical properties. The results show that medium-sized PCM fractions (1.6–2.0 mm) with moderate content (≈10% by weight) offer the most favorable compromise between insulation and strength, while thicker fractions (2.0–2.5 mm) maximize thermal energy storage capacity. These findings confirm the possibility of incorporating natural PCMs into geopolymer foams to create multifunctional materials for sustainable and energy-efficient building applications. A unique contribution to this work is the use of diatomite as a natural PCM carrier, ensuring stability, compatibility, and environmental friendliness compared to conventional encapsulation methods.

In recent years, circular economy principles have become a key paradigm in the design and evaluation of industrial processes, including recycling technologies. Direct recycling of used lithium-ion batteries is attracting particular attention, as it can significantly reduce energy consumption, reagent costs, and the carbon footprint of the entire process compared to traditional hydro- and pyrometallurgical methods. This paper provides an overview of the current state of knowledge, synthesizes contemporary methods of Li-ion battery cell recycling, and presents the most important achievements in the field of direct recycling, with particular emphasis on the regeneration and re-leaping of cathode materials, and discusses the implementation and economic premises. Key challenges and research gaps are also identified, including the need to use computational modeling (CFD/DEM, kinetic and data-driven models) to optimize the deactivation, separation, and regeneration stages. This review concludes that direct recycling has the potential to become the leading circular economy pathway for Li-ion batteries, provided that quality standardization and process modeling tools are developed in parallel.

Diatomite’s most common application is its use as a sorbent for petroleum substances. Since paraffin is a petroleum derivative, this paper investigates the sorption capacity of diatomite to absorb it. In this paper, the physical and chemical properties were studied for 4 different fractions of diatomite (0–0.063 mm; 0–2 mm; 0.5–3 mm; and 2–5 mm) in the crude and calcined states, and the sorption capacity of diatomite earth for absorbing paraffinic phase-change substances was determined. The physical and chemical studies of the material included conducting an oxide chemical composition analysis using XRF, examining the composition of the mineral phases using X-ray diffraction, and determining the particle size, porosity, and thermal conductivity of the diatomite. Morphology images were also taken for all 8 diatomite variants using scanning electron microscopy. Each fraction was subjected to static calcination at 850 °C for 24 h. The results showed that the calcination of the diatomite increased the porosity of the material and reduced the thermal conductivity coefficient, and most importantly, the sorption capacity to absorb paraffins. The highest sorption capacity was characterized by calcined diatomite powder, that is, diatomite with the smallest particle size. Absorption of paraffinic substances by diatomite exceeding 200 wt.% is possible. Thus, diatomite is one of the feasible candidates for an economical and lightweight building material for making PCM composites for thermal energy storage in buildings.

Foamed geopolymer materials are increasingly studied due to their inherent fire resistance. To date, these materials have primarily been produced by casting into moulds, with foaming occurring during mixing or within the moulds, shortly before setting. For practical applications, however, it is advantageous to apply these materials directly onto surfaces with complex geometries. Although several techniques for geopolymer spraying have been described in the literature, many exhibit limitations that restrict their practical implementation. This study presents a novel spraying technology developed on a dedicated process line, enabling in situ dosing of the foaming agent immediately before application. The system integrates infrared heating to ensure controlled curing of the geopolymer. This paper outlines the design of the process line and its core functionalities while presenting selected results of material tests conducted on the obtained geopolymer coatings. Tests performed on approximately 200 m2 of surface confirmed the functionality of the process. The thermal conductivity of the sprayed foams was about 0.07 W/m-K. The inclusion of a phase-change material (PCM) in the geopolymers further enhanced their ability to store and regulate thermal energy. The adhesion strength results, consistently exceeding 1 MPa across various substrates (steel, geopolymer, gypsum board), confirmed the practical suitability of the proposed solution. This was also demonstrated by the homogeneous foamed structure obtained.

Geopolymer concretes, synthesized from industrial by-products such as fly ash through alkaline activation, have attracted considerable attention due to their favorable thermal and microstructural properties. Incorporating phase change materials (PCMs) into geopolymer matrices can improve thermal properties, making them suitable for various sustainable construction applications. The thermal properties of geopolymer concrete depend on the composition and structure of the materials used. Adding PCMs to geopolymer concrete can significantly improve its thermal properties by increasing its heat storage capacity. PCMs absorb and release thermal energy during phase transformations, which can help regulate temperature fluctuations in building materials. This feature is particularly beneficial in regions with extreme temperature fluctuations, where maintaining a stable indoor climate is crucial. Integrating organic PCMs into geopolymer matrices has been shown to improve thermal insulation. Furthermore, the microstructural analysis of geopolymer concrete containing organic PCM indicates that incorporating these materials can lead to a more homogeneous and denser microstructure. Integrating organic PCMs instead of inorganic into geopolymer concrete is a promising route to improve thermal properties and microstructural stability. The combination of geopolymer technology with PCM not only contributes to the sustainable development of building materials but also addresses the challenges of temperature regulation in buildings.

The article presents the results of research on foamed geopolymer materials as potentially dual-function building materials, combining thermal insulation properties with the ability to physically adsorb carbon dioxide. The materials were developed on the basis of fly ash, using hydrogen peroxide as a foaming agent. Two variants of the foaming agent quantity were used to assess how this quantity affects the type of porosity, thermal insulation, and CO adsorption capacity. The porous structure was characterised using mercury porosimetry and physical CO adsorption. A full analysis of their insulating and accumulating properties was also carried out. Measurements of the thermal conductivity coefficient (λ) showed that these materials have low thermal conductivity (in the range of 0.101 W/m·K), which confirms their suitability as ecological building insulators. At the same time, sorption tests performed using a physical sorption analyser confirmed the ability of selected composites to adsorb CO , with a noticeable influence of porosity parameters depending on the amount of blowing agent used on the efficiency of the process. An unexpected result of the research was the conclusion that a smaller amount of foaming agent may be more beneficial in terms of CO adsorption capacity, while maintaining similar insulation parameters. The results suggest that properly designed foamed geopolymers can serve a dual function – as insulation materials and passive CO adsorbents, thus supporting efforts towards sustainable development and decarbonisation of construction. The results obtained provide a basis for further in-depth analyses related to the possibility of using foamed geopolymers as carbon dioxide-absorbing materials.

Building envelopes with natural fibers are the future of sustainable construction, combining ecology and energy efficiency. The geopolymer building envelope was reinforced with innovative composite bars and two types of natural insulation (coconut mats and flax/hemp non-woven fabrics) were used as the core material. A 10 mol sodium hydroxide solution with an aqueous sodium silicate solution was used for the alkaline activation of the geopolymers. The purpose of this study was to confirm the feasibility of producing geopolymer composites with insulating layers made of renewable materials, which would have compressive strengths like those of C25/30-grade concrete and thermal conductivity coefficients like those of lightweight concrete. This publication presents the results of physicochemical tests on the base materials (oxide (XRF) and mineral phase (XRD) analysis as well as morphology and EDS) and studies the physical (density measurements), mechanical (flexural and compressive strength tests) and insulating properties (thermal conductivity measurements) of the finished sandwich partitions. The composites achieved a flexural strength of 7 MPa, a compressive strength of up to 30 MPa and a decrease in the thermal conductivity coefficient of about 60%. The research demonstrates contribution to sustainable construction by developing geopolymer composites, offering both structural integrity and superior thermal insulation. This innovation not only reduces reliance on traditional, carbon-intensive materials but also promotes the use of eco-friendly resources, significantly lowering the carbon footprint of construction. The integration of natural fibers into geopolymer matrices addresses key environmental concerns, advancing a rapidly growing field that aligns with global efforts toward energy efficiency, waste reduction, and circular economy principles in building design.

Geopolymers are synthesized using anthropogenic raw materials and waste from the energy industry. Their preparation necessitates an alkaline activator, which facilitates the dissolution of raw materials and their subsequent binding. At present, geopolymers are considered a promising material with the potential to replace conventional cement-based products. This research investigates foamed geopolymer materials based on fly ash, natural fibers, and phase-change materials. The study utilized three distinct types of fibers and two phase-change materials manufactured by Rubitherm Technologies GmbH of Germany. This paper presents the results of the thermal conductivity coefficient and specific heat tests on the finished foams. Additionally, compressive strength tests were conducted on the samples after 28 days. Natural fibers decreased the insulation parameter by 12%, while PCM enhanced it by up to 6%. The addition of fibers increased the compressive strength by nearly 30%, whereas PCM reduced this by as little as 14%. Natural fibers and phase-change materials had an increased heat capacity by up to 35%. The results demonstrated the material’s potential in various industrial sectors, with the primary areas of application being building materials and insulations. The findings illustrate the significant potential of these composites as energetically and environmentally sustainable materials.

Diatomites are well-known mineral materials formed thousands of years ago from the skeletons of diatoms. They are found in many places around the world and have a wide range of applications. This article presents innovative research related to the possibility of using diatomite as a filler in composites to improve their sound absorption properties. The results of the study of the effect of diatomite processing (calcination) and its degree of fineness on the sound absorption coefficient of thermoplastic composites are presented. Three fractions of diatomite (0 ÷ 0.063 mm; 0.5 ÷ 3 mm; 2 ÷ 5 mm) and its variable mass proportion (0, 25, and 50 wt.%) were used. The composites were made with flax fibers as a reinforcement, polylactide as a matrix, and diatomite as an additional filler. This paper also presents the results of oxide chemical composition, diatomite mineral phase composition, morphology, and thermal conductivity coefficient of all diatomite fractions studied. In addition, the average particle size for diatomite powder was also determined. The most important of the studies was the determination of the acoustic properties of the aforementioned composites. As a result of the tests, it was found that the smallest fraction of diatomite particles and a variant without thermal treatment give the best effect in terms of sound absorption.