Search Results (120)

This study presents the development of a one-part phosphate-activated geopolymer foam based on fayalite flotation residue from the copper industry. The solid activator consisted of triple superphosphate, enabling a dry-mix binder that requires only water addition prior to use. Foamed materials were characterized by XRD, FTIR, Mössbauer spectroscopy, DSC-TG, hot-stage microscopy, SEM-EDX and physical and mechanical testing. The foaming of the geopolymer reduced the densities between 0.753 and 2.15 g/cm³, relative porosities up to 73.6%, and compressive strengths ranging from 1.4 to 28.8 MPa. The foamed geopolymer maintained dimensional stability up to about 1000 °C. The thermal conductivity coefficient measured on large-sized specimen blocks was 0.099 W/mK at a density of 0.753 g/cm³. These results demonstrate that fayalite slag can be effectively utilized as a precursor for sustainable geopolymer foams combining low thermal conductivity, high thermal stability, and the utilization of industrial by-products. Full article

This study presents a comparative evaluation of geopolymer foams incorporating either commercially available shape-stabilized phase change materials (PCMs) or laboratory-developed diatomite–paraffin PCM granules with controlled particle size fractions ranging from <1.6 mm to >2.5 mm. All PCM variants were incorporated at a constant dosage of 7.5 wt.% to isolate the influence of PCM type on the properties of the resulting composites. The commercial materials comprised PX-4, PX15, and PX20 (Rubitherm Technologies GmbH), whereas the laboratory-developed PCM consisted of paraffin immobilized within a porous diatomite matrix to produce granular shape-stabilized composites. The experimental program included the determination of bulk density, total porosity, pore size distribution, thermal conductivity (λ), thermal resistance (R), specific heat capacity (Cp), and compressive strength. The pore structure was characterized by mercury intrusion porosimetry (MIP), while the morphology and dispersion of PCM particles within the geopolymer matrix were investigated using scanning electron microscopy (SEM). All mixtures were produced using the same alkali-activated matrix and identical curing conditions, with the PCM content maintained at 7.5 wt.%. The results demonstrated that the type of PCM significantly affected the microstructure and thermophysical performance of the geopolymer foams. The laboratory-developed diatomite–paraffin PCM provided the most favorable thermal insulation performance, exhibiting the lowest thermal conductivity (0.095 W/m·K) together with the highest thermal resistance (0.278 m²·K/W). In contrast, the commercial PX15 and PX20 materials exhibited the highest specific heat capacities (1.740 and 1.778 kJ/kg·K, respectively), indicating superior thermal energy storage capability. In addition, the estimated production cost of the laboratory-developed PCM (2.5–4.0 EUR/kg) was substantially lower than that of the commercial PX materials (approximately 20 EUR/kg), highlighting its potential as a cost-effective alternative for sustainable, energy-efficient building materials. These findings demonstrate that both commercial and laboratory-developed PCM systems can effectively enhance the functionality of geopolymer foams, although they provide different balances between thermal insulation, heat storage capacity, and production cost. Full article

The transition toward circular economy practices and CO₂ reduction goals is driving the development of new sound absorption technologies. Traditional absorbers made from mineral wool or foams provide broadband absorption; however, their production is associated with intensive energy consumption and non-renewable resources. This is why the focus has been shifting from the mere substitution of materials to integrated solutions that combine sustainability with structure. This paper reviews recent innovations in sustainable absorbers based on bio-based and recycled materials. The acoustic performance of porous materials depends on such factors such as pore structure, airflow resistivity and geometric parameters such as thickness, multi-layer structure and resonances. At the same time, additive manufacturing (AM) allows creating geometry-controlled absorbers providing advanced acoustic properties. Despite many sustainable absorbers demonstrating sufficient sound absorption properties at medium and high frequencies, their use at low frequencies remains challenging. Additionally, concerns regarding durability, flame retardance, and environmental consistency continue to limit their broader application. Yet, hybrid, multi-material strategies, particularly those combining geopolymer matrices with bio-based or recycled fillers, are identified as a promising route to address these limitations. This review outlines current trends and highlights key challenges and future directions in the design of sustainable sound-absorbing systems. Full article

Geopolymers, alkali-activated aluminosilicate materials, have gained increasing attention as sustainable adsorbents for wastewater treatment due to their low-temperature synthesis, cost-effectiveness, and ease of shaping into mechanically robust structures. Their intrinsic negatively charged framework promotes the adsorption of cationic species; however, pristine geopolymers typically exhibit moderate performance, with adsorption capacities generally below ~70 mg g⁻¹ for dyes such as methylene blue (MB) and in the range of 20–100 mg g⁻¹ for divalent metal ions. To overcome these limitations, different strategies have been developed to tailor their pore structure and surface chemistry. In particular, foaming approaches enable the production of highly porous materials with tunable pore architecture, improving mass transfer and accessibility of active sites. Moreover, functionalization with carbon-based materials (e.g., activated carbon, graphene derivatives, biochar) or zeolitic phases significantly enhances adsorption performance, with reported capacities exceeding 500 mg g⁻¹ for Pb²⁺ and up to 450 mg g⁻¹ for organic dyes in optimized systems. This review provides a comprehensive overview of recent advances in geopolymer synthesis, pore engineering, and functionalization strategies, highlighting the relationships between composition, structure, and adsorption performance. Particular attention is devoted to the comparison between carbon-based and zeolitic modifications, as well as to the role of material shaping in enabling practical applications. Overall, the combination of tunable porosity, chemical versatility, and structural integrity positions functionalized geopolymers as promising candidates for the development of scalable and multifunctional adsorbents for wastewater remediation. Full article

In an effort to explore the influence mechanism of expanded polystyrene (EPS) foam particle content on the freeze–thaw resistance of geopolymer EPS concrete (GEPSC) and realize the synergistic optimization of freeze–thaw durability and low-carbon performance, systematic tests on the apparent morphology, mass loss rate, and relative dynamic elastic modulus (RDEM) of GEPSC with different EPS contents (30%, 35%, 40%, 45%, 50%, 55%) were conducted via freeze–thaw cycle tests. A parabolic damage model was established based on the theory of damage mechanics, and comparisons were made between GEPSC and conventional EPS concrete (EPSC) in terms of microstructure and carbon emission effect. Results indicate that the freeze–thaw resistance of GEPSC exhibits a nonlinear negative correlation with EPS content, which clarifies the applicable scope of GEPSC with different EPS dosages. The fitting correlation coefficient R² of the established parabolic damage model is all higher than 0.98, which can accurately predict the evolution law of freeze–thaw damage of GEPSC. The interfacial transition zone of GEPSC is indistinct and the geopolymer matrix presents a denser structure. Compared with EPSC of the same density, the carbon emission of GEPSC is reduced by 45.3%, demonstrating that GEPSC integrates favorable freeze–thaw resistance with prominent environmental benefits. This study provides a scientific basis for the mixed proportion design and engineering application of low-carbon concrete materials in cold regions. Full article

This study presents a novel, rapidly synthesized geopolymer foam fabricated from granite industrial waste using microwave sintering, reducing the demolding time from 7 days to 3 min and the overall processing time to 24 h, while enhancing mechanical performance. Five sample compositions (G1–G5) were prepared with varying granite powder and alkaline solution ratios, cured in a microwave for 3 min, and sintered for an additional 3 min. X-ray fluorescence (XRF), compressive strength tests, water absorption, thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared spectroscopy (FTIR) were used for thorough characterization. The compressive strength increased progressively from 13 MPa (G1) to 20 MPa (G5), the total porosity decreased from 33.33% to 18.58%, the water absorption reached a minimum of 2.02% (G5), and the bulk density rose from 1.143 to 1.49 g/cm³. XRF analysis confirmed Si/Al molar ratios of 6.5–11.4, indicating enhanced aluminosilicate network development. FTIR confirmed progressive geopolymerization, with integrated Si-O-T band areas increasing from 41,900 a.u. (G1) to 44,680 a.u. (G5). The microwave sintering approach consumed over 90% less active energy than conventional thermal curing, significantly reducing associated CO₂ emissions and thereby supporting SDG 7, SDG 12, and SDG 13. These results position granite-waste-derived geopolymer foam as a high-performance, energy-efficient alternative to conventional fired bricks and cement-based construction materials. Full article

Geopolymer concretes are increasingly regarded as advanced construction materials for applications requiring high thermal and chemical resistance. This article is a continuation of previously published research and focuses on the mechanical behaviour of geopolymer concretes containing aggregates made of foamed geopolymers and lightweight mineral aggregates, such as expanded clay and perlite, intended for use in chimney flue components. The aim of the study was to determine the influence of lightweight aggregates on the relationship between thermal insulation and the strength parameters of geopolymer concretes intended for use at elevated temperatures. Foamed geopolymer aggregates were produced by a controlled chemical foaming process, followed by grinding to specific grain sizes, yielding highly porous aggregates with low thermal conductivity, reaching approximately 0.075–0.099 W/(m·K). These aggregates were used as lightweight fillers in geopolymer concretes based on class F fly ash activated with alkaline solutions. The resulting composites were designed to combine low density and high thermal insulation with adequate mechanical strength. The mechanical properties of the developed concretes were assessed on the basis of compressive strength tests on cubic specimens and tensile strength in beam bending tests, carried out in accordance with standards. The results presented confirm that the use of foamed geopolymer aggregates enables a simultaneous increase in thermal insulation and the design of ultra-lightweight structural elements with sufficient load-bearing capacity for chimney systems (including suspended ones). This combination of low thermal conductivity, reduced mass, and appropriate mechanical properties makes geopolymer concretes with lightweight mineral and geopolymer aggregates a promising alternative to traditional ceramic materials. Full article

This study evaluates the performance of foamed geopolymer concrete (FGC) incorporating rigid polyurethane (PU) waste as a partial sand replacement and aluminum powder (AP, 1%) as a foaming agent. The mixtures were based on metakaolin, fly ash, and silica fume. Fresh and hardened properties were assessed, including workability, setting time, density, compressive strength, flexural strength, splitting tensile strength, elastic modulus, water absorption, porosity, gas permeability, and chloride ion penetration. Microstructural characteristics were examined using scanning electron microscopy (SEM). The results show that moderate PU incorporation significantly enhances mechanical performance. The optimal mixture (PU30) achieved a compressive strength of 47.25 MPa at 180 days, representing a 15.6% increase compared to the control. Flexural and splitting tensile strengths improved by 19.9% and 16.7%, respectively, while the elastic modulus increased by 33.8% to 0.95 GPa. These improvements are attributed to enhanced particle packing and more efficient stress transfer within the matrix. In contrast, higher PU contents (>30%) reduced mechanical performance due to increased total porosity and weakened interfacial bonding. Durability-related properties indicated that mixtures PU20–PU30 exhibited reduced permeability and optimized pore structure, characterized by lower pore connectivity. SEM observations confirmed a denser matrix with uniformly distributed pores at optimal PU levels. Additionally, the integration of Random Forest regression with GLCM-based texture analysis demonstrated strong capability in predicting mechanical properties from SEM images. Overall, the combined use of PU waste and AP enables the production of lightweight, structurally efficient, and sustainable FGC with improved mechanical and durability performance. Full article

Urban underground construction in water-rich sandy strata produces large quantities of high-fluidity pipe-jacking spoil whose high water content, residual conditioning agents and heavy metal contaminants make conventional dewatering and landfilling increasingly unsustainable under carbon peaking and neutrality targets. This study explores a low-carbon route that converts such spoil into CO₂ foamed concrete through a coupled alkali activation–CO₂ foaming process. Ground granulated blast furnace slag and fly ash are used as geopolymer precursors, while a CO₂-based aqueous foam is introduced as both a pore-forming phase and carbon source. Single-factor tests and an L16(4⁴) orthogonal design are conducted to quantify the effects of CO₂ concentration, foam volume fraction, geopolymer dosage and alkali activator content on fluidity, setting time and compressive strength. Scanning electron microscopy (SEM) is employed to examine pore structure, gel morphology, carbonate precipitation and the interfacial transition zone around spoil particles. The results identify an optimum mix window (CO₂ 60–80%, foam 70–80%, geopolymer ≈ 20% and alkali activator ≈ 10% of solids) that delivers a fluidity above 210 mm, 28-day strength exceeding 3.0 MPa and a uniform closed-pore network. A multi-scale mechanism is proposed in which physical foaming, chemical carbonation and spoil particle immobilization act synergistically to form a dense gas–solid–soil composite suitable for in situ backfilling. Full article

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to its enrichment of heavy metals and dioxins. This article systematically reviews its generation pathways, physicochemical characteristics, and potential environmental risks, based on the literature from 2010 to 2025 sourced from Web of Science, Scopus, ScienceDirect and China National Knowledge Infrastructure. Emphasis is placed on heavy metal stabilization, dioxin degradation and resource recovery from MSWI fly ash. The mechanisms, technical advantages, and application limitations of three mainstream detoxification, including solidification/stabilization, extraction and thermal treatment, were emphasized. For instance, geopolymer achieves >99.6% Pb immobilization and electrodialytic removal rates of Cd up to 98%, while vitrification reduces the MSWI fly ash volume by >50%. A comprehensive exploration of MSWI fly ash resource utilization was conducted, covering the preparation of ceramic tiles, synthesis of glass ceramic and glass ceramic foams, processing of road substrates, and modification of cement-based composite materials. The current technological system still faces challenges such as high costs, excessive energy consumption, and secondary pollution. Future research should focus on developing green, low-carbon, and low-cost processes, improving long-term environmental stability of products and strengthening pollution source reduction control. Full article

Geopolymers have gained relevance in environmental applications, and in recent years they have been studied as sustainable adsorbent materials. Increasing their porosity remains one of the main challenges. Various methodologies have been applied for the synthesis of porous geopolymers; however, energy efficiency and environmental considerations associated with the synthesis process must be considered. This study compares two synthesis routes for porous metakaolin-based geopolymers using hydrogen peroxide as a foaming agent and two curing methods: conventional oven curing and microwave-assisted curing. Structural, physical, and chemical properties were evaluated using XRD, FT-IR, SEM/EDS, TGA, and density–porosity analyses. Additionally, a quantitative environmental assessment based on the 12 principles of green chemistry was conducted using the DOZN^TM software version 2.0. The results confirmed that the addition of H₂O₂ did not alter the geopolymeric structure, as evidenced by FT-IR and XRD, regardless of curing method. Porosity increased significantly with the foaming agent, reaching up to ~65% for conventionally cured samples and a maximum of 67% for microwave-cured geopolymers at 3 wt% H₂O₂, with a minimum bulk density of 0.79 g/cm³. High-power microwave-assisted curing reduced the synthesis time to 5 min (≈80% reduction) while promoting a more developed and interconnected macroporous structure, as observed by SEM and supported by enhanced water retention behavior in TGA analyses. The green chemistry assessment demonstrated that microwave curing presents a lower overall impact within the DOZN^TM framework, primarily associated with improved energy efficiency (GCP-6), while acknowledging that this assessment does not constitute a full life cycle analysis. Overall, microwave-assisted synthesis emerges as a more sustainable and efficient route for producing highly porous, hydrophilic geopolymers with strong potential for the adsorption of aqueous pollutants in environmental applications. Full article

The present study evaluates the electrochemical behaviour of reinforcing steel embedded in an alkali-activated eco-cellular geopolymer concrete designed for applications in environments with high chloride exposure. The material was formulated using a ternary precursor composed of fluid catalytic cracking residue (FCC), Class F fly ash, and ground granulated blast furnace slag (BFS), activated with an alkaline solution and combined with preformed foam to generate a microstructure characterised by predominantly closed porosity and low capillary connectivity. The electrochemical response of the system was assessed through open circuit potential (OCP) measurements, Tafel polarisation curves, electrochemical impedance spectroscopy (EIS), and potentiodynamic tests under accelerated exposure to NaCl solutions. The results demonstrate a markedly improved electrochemical performance, evidenced by shifts in OCP towards more noble values, reductions of 45–65% in corrosion current density (Icorr), and increases of up to fourfold in charge transfer resistance (Rct), together with the development of broader and more stable passive regions. This behaviour is attributed to the synergistic interaction between the formation of dense N-(C)-A-S-H (sodium/calcium–aluminosilicate hydrate) and C-(A)-S-H (calcium–aluminosilicate hydrate) gels, the eco-cellular architecture with low capillary connectivity, and the stable high alkalinity of the activated matrix, which collectively restrict ionic transport and promote the passive stability of the reinforcing steel—defined here by noble OCP values, low Icorr, high Rct, and sustained passive domains in polarisation curves. Overall, the findings position the developed eco-cellular geopolymer concrete as a sustainable, high-performance alternative for infrastructure exposed to chloride-rich environments. Full article

This study investigates the deterioration of the thermal and mechanical properties of geopolymer foam concrete (GFC) subjected to accelerated weathering through carbonation, salt fog, and UV radiation. GFC blocks were synthesized using metakaolin as the aluminosilicate precursor, activated with an alkaline solution consisting of 8 M NaOH and sodium silicate (Na₂SiO₃) at a NaOH/Na₂SiO₃ ratio of 0.51 wt.%. A 30% (v/v) H₂O₂ solution served as the foaming agent, and olive oil was used as the surfactant. Accelerated carbonation tests were conducted at 25 ± 3 °C and 40 ± 3 °C, under 60 ± 5% relative humidity and 5% CO₂, with carbonation depth, carbonation percentage, density, porosity, and thermal conductivity evaluated over a 7-day period. In parallel, specimens were exposed to salt fog and UV radiation for 12 weeks in accordance with ASTM B117-19 and ASTM G154-23, respectively. Compressive strength was monitored every week throughout the exposure period. Results show that carbonation temperature governs the type and kinetics of carbonate formation. The carbonation process, at 40 °C for 7 days, increased the density and reduced the porosity of GFC, resulting in a ~48% increase in thermal conductivity. Salt fog exposure led to severe mechanical degradation, with NaCl penetration reducing compressive strength by 69%. In contrast, UV radiation caused only minor deterioration, decreasing compressive strength by up to 7%, likely due to surface-level carbonation. Full article

Lithium-containing zeolites are receiving significant attention due to their intriguing properties in various industrial applications, mainly related to gas separation and catalyzed processes. This paper presents an in-depth exploration of a nucleation strategy aimed at producing porous ceramic monoliths enriched with lithium zeolites. The synthesis was obtained by means of a geopolymer gel conversion, carried out by submerging either sodium- or lithium-rich geopolymers in lithium hydroxide solutions and performing a hydrothermal treatment. A full factorial design of experiments (DoE) was adopted to investigate the effect of LiOH molarity, treatment temperature, and time on the zeolite content in the samples. The most abundant and recurring zeolites obtained were Li-ABW (ABW) and lithium edingtonite (EDI). Concerning the lithium/sodium-containing systems, the competing presence of sodium directed the nucleation towards faujasite as well, together with minor amounts of other zeolites. In contrast, in pure lithium treatment media, the samples showed just ABW and EDI as the only crystalline phases. Full article

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. Full article