Self-healing geopolymer composites represent a frontier in sustainable construction materials, capable of autonomous crack repair through intrinsic chemical reactions or extrinsic agent delivery, restoring structural integrity without external intervention. The main aim of this review is to comprehensively analyze self-healing mechanisms, performance characteristics, and further research directions in this area. The article draws from the state-of-the-art literature review with critical evaluation, enriched by representative case studies. The following issues are discussed: (1) Microstructural mechanisms of self-healing, including intrinsic (continued geopolymerization of unreacted precursors, Ca-rich phases forming CSH-like products, carbonation-induced precipitation) and extrinsic (microcapsules, vascular networks, mineral admixtures like Na2SiO3 or MgO), and their microstructural evolution during healing. (2) The currently used methods of investigating self-healing and their limitations. (3) The challenges, such as deep crack healing (>500 μm), multiple healing cycles, and environmental robustness. (4) Applications, including durable pavements and 3D-printed elements prone to shrinkage cracking. (5) Future directions emphasizing hybrid mechanisms, in situ monitoring (acoustic emission, ultrasonic testing), and life-cycle assessment. The main findings show that self-healing geopolymers advance circular economy principles by extending service life and minimizing repair costs in low-carbon infrastructure.

This research was motivated by the urgent need to address resource shortages and high energy costs in concrete production by replacing an energy-intensive traditional curing method with a new, more sustainable solution. By exploring solar heat treatment with composite binders and THACs, the study aimed to develop sustainable, cost-effective alternatives that harness renewable energy sources and optimize natural cement hydration processes for accelerated hardening. This article explores the potential application of solar energy in the production of precast concrete products using a composite binder. The effectiveness of the composite binder in solar thermal treatment of concrete using translucent heat-accumulating coatings is tested. The results of laboratory studies are presented, and the feasibility of using concrete based on composite binder at the laboratory scale for the production of concrete and reinforced concrete products, both with steaming and with solar thermal treatment, is established. The study of the structural features and basic physical and mechanical properties of hardened concrete under various conditions indicates that, under the investigated laboratory conditions, solar-thermally treated concrete exhibits physical and mechanical properties comparable to those of normally cured concrete. Laboratory studies confirmed the effectiveness of both steaming and solar heat treatment methods under controlled experimental conditions. Within the scope of the performed laboratory tests, the structure and properties of these concretes were comparable to those of normally cured concretes and, in several aspects, superior to those obtained under conventional steam curing regimes, which indicates the effectiveness of the described method, not only from the point of view of significant savings in fuel and energy resources. When producing products based on composite binders using solar thermal treatment, the consumption of the clinker portion of the binder is reduced by 50% (composition of the composite binder itself) and the consumption of conventional fuel during heat and moisture treatment is reduced by 70–100 kg per 1 m3 of concrete (reflecting process-level comparisons), which is of significant value for external energy demand. These findings confirm the technical feasibility and environmental advantages of the proposed method at the laboratory scale and highlight its potential for broader industrial application in precast concrete production.

The massive accumulation of petrochemical-derived gypsum (PDG) poses significant environmental management challenges, necessitating innovative valorization strategies within the circular economy. This study investigated the engineering feasibility and ecological safety of repurposing gypsum as a functional aggregate substitute in the production of controlled low-strength materials, aiming to reduce reliance on natural resources while effectively managing industrial waste. The experimental program was conducted in two distinct stages using a binder system of Type I Portland cement and Class F fly ash. Stage I evaluated the potential of maximum waste diversion by completely replacing natural fine aggregates with gypsum (100% replacement). Stage II focused on optimizing the mix for industrial viability by reducing the gypsum content to 50% and 37%, thereby partially reintroducing natural coarse and fine aggregates to improve volumetric stability. The study assessed mechanical properties through compressive strength testing under air-curing and water-curing regimes. It evaluated environmental impact via seawater immersion tests, pH monitoring, and toxicity characteristic leaching procedures. The investigation revealed that the 100% PDG mixture achieved a 28-day compressive strength of 4.69 MPa due to an ettringite-driven air-hardening mechanism but exhibited moisture sensitivity. Conversely, the 37% PDG substitution yielded the highest strength (4.72 MPa) with superior volumetric stability. Leaching assessments confirmed that heavy metal concentrations and pH remained within regulatory limits. Consequently, the 37% replacement ratio provided the optimal balance between mechanical performance and durability, validating the feasibility of materials for sustainable coastal infrastructure and road sub-base applications.

The pollution of water, including salt and fresh water, has become an emergency problem. Pollutants come from different sources and have various characteristics, starting from industry and fertilizers used in agriculture, sewage related to human living, and other sources. Diverse sources of pollution require a comprehensive approach to water purification. One possible approach may be the use of appropriate sorbents. Currently, one of the most promising materials used is zeolites. This is because they can come from various sources, including waste raw materials such as fly ash, and, therefore, allow for the use of a circular economy approach. Moreover, these materials can be modified, which enables their selective use for selected types of pollutants. Eventually, these materials become economically viable options. The main aim of this article is to present and analyze possible solutions to water pollution based on zeolite materials. For this purpose, a critical literature review was prepared. The review reveals that zeolites perform particularly well in ion-exchange-driven removal of inorganic contaminants, while their effectiveness for organic micropollutants under realistic conditions is often limited. The identified trade-offs between removal efficiency, regeneration stability, and scalability indicate that zeolites are best applied as function-specific rather than universal sorbents. From a sustainability perspective, this targeted applicability is supported by advantages, such as low material cost, long service life, and the possibility of using naturally occurring or waste-derived precursors, which, together, enable resource-efficient water treatment processes, reduced reliance on energy-intensive technologies, and the valorization of industrial byproducts within circular economy frameworks.

This work supports the circular economy and sustainable material by facilitating the creation of low-carbon materials with enhanced elimination of nutrients from wastewater, thereby assisting in preventing eutrophication. Porous geopolymers, owing to their distinctive pore structure and numerous superior properties, including noise reduction and thermal insulation, have a wide range of potential applications in the building sector, chemical industry, and water treatment. Developing low-carbon-footprint porous geopolymer materials is an important step toward creating multipurpose lightweight materials that can serve as structural materials and, at the same time, as adsorbents. In this study, it was revealed that the porous material created during the hydrothermal synthesis of (lime-Portland cement-based aerated composition), by replacement of sand with wood biomass bottom ash (WBA), can be used as porous aggregates (PA) for adsorbent development. PA was produced with an apparent porosity of 65%, a density of 610 kg/m3, and a compressive strength of 2.0 MPa. The effectiveness of employing an air-entraining additive (AEA) and creating PA in geopolymers was tested. A different-molarity activator was used, and wood biomass fly ash (WFA) and metakaolin (MK) waste were used as precursors for the synthesis of porous geopolymers. Using an air-entraining admixture in geopolymers allows for the production of lightweight geopolymers with densities up to 1400 kg/m3, compressive strengths up to 8.0 Mpa, and apparent porosities up to 38.4%. Such properties, together with their low cost, offer good prospects for geopolymers in the construction industry. By utilizing PA in the geopolymer composition, a lightweight geopolymer (GPA) with a density of 985 kg/m3 and a compressive strength of 3.9 Mpa, with 42.0% apparent porosity, was obtained. The materials effectively removed phosphorus from biologically treated wastewater: PA had an efficiency of up to 82.5%, the geopolymer with AEA had an efficiency of up to 88.4%, and GPA had an efficiency of up to 97%. The created GPA enhances the adsorbent's sorption capacity, resulting in extremely high phosphorus uptake efficiency.

Developing 3D-printable materials that address buildability limits and environmental sustainability is a critical challenge. This study introduces a novel print-rest-print strategy for a self-activating cementless mortar (CM) incorporating ground granulated blast-furnace slag and co-fired fly ash. Under controlled isoworkability conditions, the extended setting time of CM was exploited to increase buildability to 30 layers without chemical accelerators. Furthermore, the optimized aggregate skeleton enabled a multifunctional composite that delivered robust compressive structural strength (>20 MPa) at 56 days while achieving lower thermal properties (0.58 to 0.88 W/m & centerdot;K), achieving a 65% reduction compared to the midpoint of reported conventional mortars. This multifunctional cementless material presents a highly sustainable, energy-efficient alternative for advanced additive manufacturing in construction.

Nano-silica (nano-SiO2) has emerged as a powerful designer tool for engineering the microstructure of geopolymer composites, enabling precise control over porosity, interfacial transition zone (ITZ) characteristics, and resultant mechanical performance. The main aim of this review is to evaluate the role of nano-silica as a reinforcement and pozzolanic accelerator. The paper delivers a critical literature overview. It is based on a comprehensive critical review of the existing literature and illustrative case studies demonstrating practical applications in geopolymer composites. The article presents the key mechanisms connected with the application of nano-additives, including accelerated geopolymerization kinetics and heterogeneous nucleation on nano-silica surfaces. Comprehensive characterization methods are critically assessed, including SEM/EDS for gel morphology, MIP for porosity profiles, XRD/FTIR for reaction products, micro-CT for 3D void networks, and nanoindentation for ITZ mechanical gradients. The article also shows the main applications span high-performance concretes, 3D-printed geopolymer elements (improved buildability and interlayer adhesion), and durable overlays. The article is a closed presentation of challenges such as long-term stability, alongside future directions. The main findings show that nano-silica offers a pathway to tailored, low-carbon geopolymers with superior microstructure-performance relationships aligned with sustainable construction goals.

Fused deposition modelling (FDM) is increasingly used to produce high-performance polymer components; however, the mechanical performance of printed parts is often limited by weak interlayer adhesion, void formation, and residual thermal stresses. In this study, the effects of nozzle temperature, bed temperature, and post-treatment annealing temperature on the tensile and flexural strength of FDM-printed polyether ether ketone (PEEK) were investigated and optimized using Response Surface Methodology (RSM). A face-centred central composite design was employed to evaluate the individual, quadratic, and interaction effects of the three thermal parameters. The results showed that post-treatment annealing temperature was the most influential factor, contributing 56.48% to tensile strength and 52.73% to flexural strength, followed by nozzle temperature, which contributed 30.56% and 30.15%, respectively. Bed temperature showed a comparatively smaller individual effect; however, its interaction with nozzle temperature significantly influenced both tensile and flexural strength. The confirmation experiment performed at 200 °C post-treatment temperature, 414 °C nozzle temperature, and 142 °C bed temperature produced a tensile strength of 55.65 MPa and a flexural strength of 81.08 MPa, with prediction errors of 5.63% and 4.08%, respectively. SEM fracture analysis provided qualitative evidence that improved thermal processing reduced interlayer separation and visible void-related defects while promoting a more cohesive fracture morphology. These improvements are attributed to enhanced interlayer fusion, possible polymer-chain diffusion across layer boundaries, and thermal-stress relaxation during annealing. The findings demonstrate that thermal-parameter optimization and post-treatment annealing can improve the mechanical performance of FDM-printed PEEK within the investigated processing window.

There is a pressing need to develop carbon fiber composites with sustainable fillers that enhance their strength without increasing costs or environmental impact. Such advancements would not only improve performance in high-stress applications but also align with global sustainability goals by utilizing eco-friendly materials and reducing waste. This study explores the use of biochar derived from fish scales as a sustainable filler material in carbon fiber epoxy composites. The biochar was produced through pyrolysis and incorporated into the composites at various weight percentages (0 %, 1 %, 3 %, 6 %, 9 %, 12 %, and 15 %). Mechanical properties, including tensile strength, flexural strength, impact strength, and interlaminar shear strength, were evaluated according to ASTM standards. The results demonstrated that the incorporation of biochar significantly improved the mechanical properties of the composites, with optimal performance observed at 9 % biochar content. At this concentration, the tensile strength increased by 60.02 %-674.21 MPa, the tensile modulus by 74.96 % to 46.05 GPa, the flexural modulus by 58.32 GPa, and the impact strength reached 102.32 kJ/m2. It was found that achieving the optimal performance requires an optimal weight percentage of biochar. This study highlights the potential of fish scale-derived biochar as an effective and sustainable filler material for enhancing the performance of carbon fiber composites.

Additive manufacturing brings many benefits to the building industry, one of them being automatization and the possibility to work in harsh environments, including underwater applications. In addition, this technology enables faster infrastructure repairs and adjustments to the scope of work to specific damage caused by, for example, biocorrosion processes. The main aim of this article is to investigate the development of geopolymers as a printable material for civil engineering, including underwater applications. For that purpose, the process of the material extrusion will be modified, and material properties will be improved. In the first step, the raw materials were investigated (SEM, EDS, XRF, particle size analysis) and the proper additives were selected based on literature analysis. Next, geopolymer paste was synthesized and fresh paste properties were investigated, including time for curing samples and workflow. The mixture composition was modified to obtain the required printable parameters through the application of different additives and the modification of the proportion of components, especially alkali solution. Finally, small-scale additive manufacturing trials were conducted in the air and with submerged containers. Additionally, samples were prepared using the casting method to compare the mechanical properties and microstructure. The obtained results show that additives such as xanthan gum and superplasticizer improve the rheological properties of the paste efficiently. With the help of additive manufacturing, geopolymer samples with compressive strengths of up to 7.5 MPa and flexural strengths of up to 4.15 MPa after 28 respectively were achieved. Compared to the average of the cast samples, the compressive strength of the printed samples was at least 5% lower, while the flexural strength was at least 38% lower for printed samples. The 3D-printed samples showed strong anisotropy between the tested orientations of the flexural strength samples.

One of the most important areas of the construction industry is road infrastructure. It plays a crucial role in the economy of various countries. Today’s roads must withstand long-term temperature and load differences, but some of the infrastructure cannot survive these tests, and after one severe winter, there may be asphalt cracks and holes that need to be repaired. This problem requires new applications and more resistant materials. Geopolymers are potential candidates. This class of material as a building material for roads has the potential to withstand frost and salt. The aim of the study herein is to demonstrate the mechanical and physical properties of a composite geopolymer made from fly ash, coal shale, nanosilica, and carbon fiber for potential application in road infrastructure. The research and experiments herein will serve to determine whether geopolymers are suitable for replacing traditional concrete in road construction processes. The following research methods were applied: SEM, XRF, XRD, compressive strength testing, abrasion, and investigation of freeze–thaw resistance in a climatic chamber. The results confirm the potential possibility of applying geopolymer compositions in road infrastructure, including sufficient mechanical properties such as ca. 38 MPa and freeze–thaw resistance, as shown by mass loss of about 1.7%, as well as sufficient abrasion resistance, as shown by mass loss of about 4%.

Geopolymers are inorganic aluminosilicate binders formed by alkali activation of reactive powders, offering a sustainable, low-carbon alternative to Portland cement. Their rapid setting and chemical durability make them well-suited for additive manufacturing (AM) in demanding environments, including underwater construction, where chemical stability is essential for both structural integrity and environmental safety. This study evaluates two metakaolin-based formulations designed for underwater extrusion, differing in activator chemistry and rheology control. Standardized leaching tests revealed alkaline but stable leachates with strong immobilization of most ions; major anions and total dissolved solids remained within regulatory thresholds. Limited exceedances were observed-soluble organic carbon in the NaOH-activated mix and arsenic/selenium in the waterglass-sand system-highlighting specific areas for mix improvement rather than fundamental limitations of the material. Complementary radioactivity screening confirmed activity concentration indices well below the regulatory limit, with measured radionuclide activities falling comfortably within exemption ranges. Together, the leaching and radioactivity results demonstrate that both formulations provide robust matrix integrity and environmental compatibility, while highlighting clear opportunities for mix design improvements to further minimize ecological risks.

Peculiarities of the structure formation of surface layers on 12Cr18Ni10Ti steel under the action of femtosecond laser irradiation were investigated. The effect of the scanning speed of the laser beam on the formation of surface microrelief and possible phase transformations was evaluated. The formation of a peculiar microrelief of the surface can be explained by the complex effect of laser irradiation, which intensifies the redistribution of alloying elements of steel in the surface layers, changing their elemental composition in some places, initiates deformational phase transformations, and promotes fragmentation and grinding of the microstructure.

The main aim of this research was to synthesize the new geopolymer composite and test its antibacterial properties. The new composites are based on a geopolymer matrix, with the addition of carbon fiber, nano-silica and antibacterial nanopowder. The first stage of this research was the synthesis of geopolymer composites containing variable proportions of nano-additives and, as a reference material, cement. The next step was bacterial cultivation. Two different bacterial strains were selected, Gram-positive and Gram-negative (Escherichia coli and Staphylococcus aureus). In this stage, the agar microbiological medium is used for the evaluation of bacterial growth inhibition by cement and geopolymers. In the final stage, the growth of the colony was observed and the pH measurements were taken. The final assessment of efficiency was made by using optical microscopy and a colony counter based on the Petri dish. The test performed showed that the main mineralogical components are quartz, 55.0%, and mullite, with 42.1% of crystalline ingredients. EDS analysis shows that the main oxide component is SiO2, about 50.9%. The obtained results connected with bacteria growth show the growth of both types of bacteria on materials; however, after several days, the growth was inhibited. An assessment of microorganism growth inhibition by cement and geopolymers shows the better efficiency of geopolymer composites in this area for both types of colonies (Gram-positive and Gram-negative). The new element in this research was to plan the research from the point of view of its application in the water environment. The provided research can be useful for the inhibition of biofouling phenomena on marine and inland water infrastructure.

The main motivation for this research work was the need to find new ways of managing process byproducts of combustion in a way that is safe for the environment and human health. The paper presents research confirming the applicability of the geopolymerization process to stabilize slags and ashes from municipal waste incineration plants. The article aims to assess the possibility of preparing geopolymer materials based on slags and ashes from the process of thermal transformation of municipal waste. The first stage of the work was the characterization of the raw materials used for research using microstructural tests (scanning electron microscopy, x‐ray fluorescence and x‐ray diffraction). The next stage was the synthesis of the geopolymer material based on the above‐mentioned byproducts of the combustion process, including obtaining appropriate samples i. e., beams and cubes. The initial stage of work indicated the need to combine geopolymer materials with the content of slag and fly ash of post‐process origin after the thermal transformation of municipal waste, mixed with another additive to improve the cohesion of the material. For this purpose, another product, which came from thermal transformation processes, was used ‐ fly ash from the coal‐fired power plant. Then, selected physical and mechanical properties of the prepared materials were determined, including: density, compression and bending tests and water absorption. The microstructure of the obtained materials was also characterized. The obtained results were assessed in terms of the possibilities of using new materials in the construction industry.

This article presents experimental studies on the characterization of geopolymer composites intended for applications in aquatic environments, with particular emphasis on underwater infrastructure. The motivation for conducting the research was the growing need to develop durable and ecological building materials that will be resistant to long-term exposure to moisture and aggressive chemical agents, typical for the underwater environment, where traditional cement concretes undergo gradual degradation due to long-term water impact, including hydrotechnical and underwater infrastructure. Geopolymer binders were produced based on metakaolin activated by alkaline solutions containing sodium hydroxide. Several series of mixtures with additives such as blast furnace slag, amphibolite and carbon fibers were developed to evaluate the effect of these components on mechanical strength, water absorption and chemical durability. The conducted studies showed that slag additions improved mechanical properties, for the best composition it across 50 MPa. In contrast, the addition of amphibolite had an unfavorable effect, which probably results from introducing inhomogeneity into the material structure. The presence of carbon fibers promoted matrix cohesion, but their uneven distribution could lead to local strength differences. Water absorption tests have shown that geopolymers reach full water saturation within 24 to 48 h, which indicates rapid establishment of capillary equilibrium and limited further water penetration. The conclusions from the work indicate that geopolymer composites with a moderate amount of blast furnace slag and subjected to appropriate curing conditions. High strength, water and chemical resistance make them suitable for, among others, the construction of marine foundations, protection and structural shields of submerged applications.

Despite the availability of various materials for chimney applications, ongoing research seeks alternatives with improved thermal and chemical resistance. Geopolymers are a promising solution, exhibiting exceptional resistance to high temperatures, fire, and aggressive chemicals. This study investigates fly ash-based lightweight geopolymer concretes that incorporate expanded clay aggregate (E.C.A.), perlite (P), and foamed geopolymer aggregate (F.G.A.). The composites were designed to ensure a density below 1200 kg/m3, reducing overall weight while maintaining necessary performance. Aggregate content ranged from 60 to 75 wt.%. Physical (density, thickness, water absorption), mechanical (flexural and compressive strength), and thermal (conductivity, resistance) properties were evaluated. F.G.A. 60 achieved a 76.8% reduction in thermal conductivity (0.1708 vs. 0.7366 W/(m·K)) and a 140.4% increase in thermal resistance (0.1642 vs. 0.0683). The F.G.A./E.C.A./P 60 mixture showed the highest compressive strength (18.069 MPa), reaching 52.7% of the reference concrete’s strength, with a 32.3% lower density (1173.3 vs. 1735.0 kg/m3). Water absorption ranged from 4.9% (REF.) to 7.3% (F.G.A. 60). All samples, except F.G.A. 70 and F.G.A. 75, endured heating up to 800 °C. The F.G.A./E.C.A./P 60 composite demonstrated well-balanced performance: low thermal conductivity (0.2052 W/(m·K)), thermal resistance up to 1000 °C, flexural strength of 4.386 MPa, and compressive strength of 18.069 MPa. The results confirm that well-designed geopolymer lightweight concretes are suitable for chimney and flue pipe linings operating between 500 and 1000 °C and exposed to acidic condensates and aggressive chemicals. This study marks the initial phase of a broader project on geopolymer-based prefabricated chimney systems.

The present work is the first study exploring the potential of geopolymer foams based on fayalite slag, an industrial by-product, as the primary precursor, for lightweight and fireproof construction applications. The research involved the synthesis and characterization of geopolymer foams with varying water to solid ratio, followed by testing their physical and mechanical properties. The phase composition and microstructure of the obtained geopolymer foams were examined using powder XRD, Micro-CT and SEM. The geopolymer foams at optimal water to solid ratio (0.15) demonstrated 73.2% relative porosity, 0.92 g/cm3 apparent density and 1.3 MPa compressive strength. The use of an air-entraining admixture improved compressive strength to 2.8 MPa but lowered the relative porosity to 64.5%. Real-size lightweight panel (300 × 300 × 30 mm) specimens were prepared to measure thermal conductivity coefficient (0.243 W/mK) and evaluate size effect and the reaction to direct fire. This study demonstrates the successful preparation of geopolymer foam products containing 81% fayalite slag, highlighting its potential as a lightweight, insulating and fire-resistant material for sustainable construction applications.

Geopolymer concrete reinforced with MiniBars™ could be an eco-friendly, innovative, durable, high-strength material substitute for common Portland cement in buildings. AR glass fiber MiniBars™ composites (AR MiniBars™) (ReforceTech AS, Royken, Norway) 60 mm in length were utilized to strengthen the geopolymer matrix for the fabrication of unidirectional geopolymer composites reinforced by AR MiniBars™ (AR MiniBars™ FRBCs). New AR MiniBars™ FRBCs were fabricated by adding different amounts of AR MiniBars™ (0, 12.5, 25, 50, 75 vol.%) into the fly ash geopolymer paste. Geopolymers were obtained by combining fly ash powder with Na2SiO3/NaOH in a ratio of 2.5:1, which served as an alkaline activator. AR MiniBars™ FRBCs were cured for 48 h at 70 °C and tested for different mechanical properties. Fly ash, AR MiniBars™, and AR MiniBars™ FRBC were evaluated by optical microscopy and SEM. The addition of AR MiniBars™ increased the mechanical properties of AR MiniBars™ FRBCs. The mechanical properties of AR MiniBars™ FRBCs were heightened compared to the geopolymer without AR MiniBars™; the flexural strength was 18.80-30.71 times greater, the flexural modulus 4.07-5.25 times greater, the tensile strength 3.49-8.27 times greater, the force load at upper yield tensile strength 3.6-7.72 times greater, and the compressive strength for cubic samples 2.75-3.61 times greater. The fractured surfaces and sections of AR MiniBars™ FRBCs were inspected by SEM and optical microscopy analyses, and even though there was no chemical adhesion, we achieved a good micromechanical adhesion of the geopolymer to AR MiniBars™. These results obtained encouraged us to propose AR MiniBars™ FRBCs for application in construction.