Search Results (1,004)

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

High-plasticity clays (CH) are widely recognized in geotechnical engineering for their poor engineering behavior, including low shear strength, high compressibility, and swelling potential, yet their presence in infrastructure projects is often unavoidable. This study investigates a sustainable alternative to ordinary Portland cement (OPC) by evaluating the durability of soil–geopolymer mixtures (SGMs) incorporating quarry dust (QD), an industrial by-product from sand and gravel operations in the Philippines. Durability assessment was emphasized due to the country’s tropical climate, marked by alternating wet and dry seasons that may accelerate deterioration of stabilized soils. QD was activated using sodium silicate (SS) and sodium hydroxide (SH) and blended with CH to form SGMs. Index property tests were conducted to characterize raw materials and identify optimal mix proportions. After 28 days of curing, specimens were subjected to wetting–drying (WD) cycles consisting of 5 h of water submersion and 42 h of oven-drying at 70 °C. Mass loss and surface degradation were evaluated by brushing in accordance with ASTM procedures. The SGMs exhibited an average mass loss of 6.83% after 12 WD cycles, satisfying the Portland Cement Association (PCA) criterion of less than 7.00% for stabilized clays. These results demonstrate that QD-based geopolymers are a viable and sustainable stabilizer for CH soils in tropical environments. Full article

Against the backdrop of rapid development in low-carbon building materials, geopolymer mortar has become a high-quality alternative to traditional cement-based materials due to its advantages of environmental friendliness, high strength, and excellent durability. However, its inherent brittleness and tendency to crack severely limit its widespread adoption and use in engineering. To mitigate the inherent brittleness of geopolymer mortar, this study developed a ternary binder system composed of metakaolin, slag, and fly ash. The effects of basalt fiber contents of 0%, 0.25%, 0.50%, 0.75%, 1.00%, and 1.25% by mass on the flowability, flexural strength, compressive strength, and deformation behavior of the geopolymer mortar were systematically investigated. The evolution of the displacement and strain fields during flexural and compressive loading was monitored in real time using two-dimensional digital image correlation (2D-DIC). The fiber-reinforcement mechanism was further examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results show that basalt fiber reduces mortar flowability, and the reduction becomes more pronounced with increasing fiber content. The flexural strength first increased and then decreased with increasing fiber content; at 0.50% fiber content, the 28-day flexural strength reached 12.6 MPa, which was 8.2% higher than that of the fiber-free control. The compressive strength increased only slightly at a low fiber content of 0.25% and then decreased when the fiber content exceeded 0.50%. The 2D-DIC results indicate that a moderate fiber content (0.50–0.75%) markedly increased the ultimate displacement, delayed crack propagation, and enhanced the post-cracking deformation capacity. Microstructural observations revealed that an appropriate fiber content promoted good interfacial bonding with the matrix and enabled fiber bridging and crack resistance. In contrast, excessive fiber addition caused agglomeration-induced micropores and microcracks, thereby degrading mechanical properties. Overall, the recommended basalt fiber content is 0.25–0.50%. These findings provide a theoretical and experimental basis for optimizing high-performance, low-carbon geopolymer mortar for engineering applications. Full article

To lower the water absorption capacity and enhance the anti-corrosion performance of geopolymer coatings, methyltrimethoxysilane (MTOS) was adopted as a hydrophobic modifier to synthesize hydrophobic geopolymer coatings, and their anti-corrosion behaviors were systematically investigated. The results reveal that increasing MTOS content gradually improves the fluidity and setting time of fresh coatings while reducing their bonding strength. MTOS effectively strengthens the surface hydrophobicity of the coatings, decreases the water absorption of coated concrete substrates, and remarkably boosts chloride ion penetration resistance. The modified coatings achieve the optimal anti-corrosion performance at an MTOS dosage of 8 wt.%. Under this optimal condition, the surface water contact angle reaches 135.1°. After 28 days of chloride ion erosion, the chloride ion concentration is 45.0% lower than that of the unmodified counterpart. Meanwhile, the coating exhibits the minimum water absorption rate of 2.06% and the lowest average chloride penetration rate of 0.41 × 10⁻³ mg/(cm²·d), which accounts for only 41% of the standard threshold value. This study demonstrates that MTOS-based hydrophobic modification can significantly upgrade the anti-corrosion capability of geopolymer coatings, which provides a valuable theoretical basis and practical guidance for improving the durability of concrete structures. Full article

Geopolymer EPS concrete (GEPSC) is a promising low-carbon lightweight material for building envelope and thermal insulation applications. In order to investigate the effects of expanded polystyrene (EPS) content on the lightweight characteristics and mechanical properties of geopolymer EPS concrete (GEPSC), specimens with EPS volume contents of 30%, 35%, 40%, 45%, 50%, and 55% were prepared. Dry density, cube compressive strength, axial compressive strength, splitting tensile strength, flexural strength, and elastic modulus were tested, and empirical relationships among the main mechanical parameters were established. The results show that dry density, cube compressive strength, axial compressive strength, splitting tensile strength, and elastic modulus decrease with increasing EPS content, indicating a clear lightweighting–strength reduction effect. The low strength and low stiffness of EPS particles weaken the continuity and load-bearing skeleton of the geopolymer matrix, while promoting more dispersed crack propagation and a more gradual failure process. The correlation coefficients of the proposed empirical models are all greater than 0.90. Lightweighting efficiency analysis indicates that an EPS content of 40–45% provides a favorable balance among weight reduction, strength retention, and stiffness retention. Compared with EPS concrete, GEPSC exhibited 23.5–49.5% higher strength at the same density grade, indicating its good strength retention capacity and potential engineering applicability. These findings support mix optimization, mechanical parameter selection, and engineering application of low-carbon lightweight envelope materials. Full article

The growing demand for sustainable construction materials has led to significant advancements in ultra-high-performance concrete (UHPC), with a particular focus on geopolymer-based systems as an alternative to conventional cementitious binders. This review explores the latest developments in sustainable Ultra-High-Performance Geopolymer Concrete (UHPGPC) by analysing key material composition, mechanical, durability and microstructural properties. The incorporation of ground granulated blast furnace slag (GGBFS), silica fume (SF), and fly ash (FA) has demonstrated notable improvements in compressive strength, durability, and workability. Additionally, the use of activators such as sodium silicate and sodium hydroxide optimizes geopolymerization, resulting in a denser microstructure and enhanced mechanical performance. This review highlights the critical role of fibre reinforcement in UHPGPC, where steel fibres (SFs) and hybrid fibres significantly enhance compressive and tensile strength, as well as crack resistance. The inclusion of waste materials such as rice husk ash and recycled glass promotes sustainability by reducing CO₂ emissions while maintaining structural integrity. However, higher waste-glass content may adversely affect bonding due to its smooth surface texture. The findings highlight the potential of UHPGC as a high-performance, eco-friendly alternative to traditional cement-based UHPC. By integrating industrial by-products and alternative activation techniques, UHPGPC can contribute significantly to the global shift towards sustainable and low-carbon construction materials. 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

The construction industry contributes significantly to global CO₂ emissions, primarily due to the production of ordinary Portland cement (OPC). As a sustainable alternative, geopolymer concrete, utilizing industrial by-products, such as ground granulated blast furnace slag (GGBFS) and fly ash (FA), has attracted increasing attention. However, studies on the post-fire behavior of high-strength slag–fly ash-based geopolymer concrete (HSSFGC) remain limited. In this study, two HSSFGC mixtures with FA contents of 10% and 30% were prepared and exposed to elevated temperatures of 100 °C, 300 °C, 450 °C, and 600 °C. After natural cooling, mass loss, ultrasonic pulse velocity (UPV), residual compressive strength, and microstructural evolution were investigated using XRD, FTIR, TGA, SEM, and EDS techniques. The results show that as temperature increases, mass loss and internal defects also increase, accompanied by deterioration of the interfacial transition zone (ITZ). At 100–300 °C, specimens with higher FA content exhibited improved residual compressive strength due to secondary geopolymerization of unreacted FA. However, above 300 °C, all specimens experienced significant strength degradation, with residual compressive strength at 600 °C reduced to 57% for FA-10 and 49% for FA-30 of their respective room-temperature values. This mix-specific difference, attributed to higher pore connectivity and more severe dehydroxylation in FA-30. These findings reveal the temperature-dependent degradation mechanisms of HSSFGC and provide a theoretical basis for post-fire assessment and sustainable engineering applications. Full article

The successful application of extrusion-based 3D-printed geopolymer mortars largely depends on precursor chemistry, activator composition, mixture proportions, and fresh-state behavior, which is highly sensitive to time-dependent structural build-up. This review examines the relationships among mix design, geopolymerization chemistry, rheological properties, and printability requirements for 3D-printed geopolymer mortars. Particular emphasis is placed on the effects of precursor type, alkaline activator characteristics, liquid-to-solid ratio, additives, and fibers on flowability, yield stress, viscosity, extrudability, buildability, shape retention, and interlayer bonding. The review further discusses how geopolymerization kinetics influence the evolution of fresh-state properties, the printable time window, and the transition from extrusion to structural stability. In addition, early-age performance is evaluated in terms of setting behavior, green strength development, and layer-interface integrity. Current challenges, including the lack of standardized test methods, limited comparability among published studies, and the complex coupling between material design and process parameters, are also highlighted. Finally, the review identifies key research gaps and proposes future directions for developing robust, printable, and sustainable geopolymer mortar systems for additive manufacturing in construction. Full article

Using solid wastes to fabricate sustainable backfill materials for mining engineering is crucial for environmental sustainability worldwide. In this study, the use of coal gangue aggregates as a sustainable alternative to natural aggregates in geopolymer gel backfill materials was explored, which contributes to green mining development. Through uniaxial compression tests, the effects of fine gangue content, mass concentration, and the binder content of geopolymer backfill materials on the compressive behavior of coal gangue geopolymer gel backfill–rock combinations (CGBRC) were systematically evaluated. Digital Image Correlation (DIC) and acoustic emission (AE) techniques were employed to reveal the strain field evolution and damage progression of CGBRC. Results show that as the content of fine coal gangue increases, the compressive strength first increases and then decreases. Compared with the compressive strength at a 20% content, the compressive strength at a 40% content increased by 33.2%, while the elastic modulus increased by 11.2%. Meanwhile, with the increase in mass concentration and binder content, the compressive strength and elastic modulus of coal gangue geopolymer filling materials show an increasing trend, reaching peak values at 86% mass concentration and 32% binder content, respectively. The strain concentration zones mainly form near the backfill interface, with propagation paths governed by backfill strength. Damage evolution undergoes three stages including rapid accumulation during compaction, gradual development in the elastic-plastic stage, and abrupt acceleration at failure. The interfacial debonding behavior is primarily influenced by the strength difference between the backfill and surrounding rock. Specimen failure is dominated by brittle shear fracture, categorized into three modes based on crack paths relative to the backfill, which include penetrating backfill failure, axisymmetric interface failure, and centrally symmetric interface failure. These findings offer theoretical and technical support for coal gangue resource utilization and green mining practices, advancing sustainable solid waste management. Full article

The increasing generation of ceramic waste from manufacturing defects, construction activities, and demolition operations poses significant environmental and waste management challenges worldwide. This study presents a preliminary investigation into the incorporation of ceramic waste aggregates (CW) as partial and full replacement for natural coarse aggregates in fly ash-based geopolymer concrete (GPC) under water-curing conditions. Five mix compositions were prepared with ceramic waste aggregate replacement levels of 0%, 20%, 40%, 60%, and 100%. Fresh and hardened properties were evaluated using flow table and early-age compressive strength tests at 7 and 14 days. The 20% replacement mix achieved the best compressive strength value of 5.52 MPa at 14 days, slightly exceeding the control GPC mix (5.09 MPa) among the limited mixtures investigated in this preliminary study. However, higher replacement levels resulted in reduced compressive strength, which may be associated with increased porosity, weaker aggregate–matrix bonding, and limitations related to the adopted water-curing regime. Workability remained within acceptable flow ranges for most mixes, although reduced flowability was observed for the 40% replacement. The comparatively low strength values obtained across all mixtures may largely be associated with the absence of heat curing and the inclusion of additional water to improve workability, both of which likely limited the geopolymerization efficiency. Based on the comparatively low compressive strength values obtained, the investigated mixtures, in their current form, are only suitable for low-strength or non-structural applications rather than structural concrete applications. Overall, this study provides preliminary insights into the influence of ceramic waste coarse aggregates on the workability and early-age compressive strength behavior of fly ash-based geopolymer concrete under the adopted experimental conditions. Further optimization of the curing regimes, mix design parameters, and long-term mechanical and durability performance is necessary before broader engineering applicability can be established. Full article

This study explores the real-time aging of a 15-year-old uncalcined kaolinite-based geopolymer (UKG). The significance of this research lies in the fact that uncalcined kaolinite-based geopolymer is a relatively new material tailored for diverse applications, including construction, water treatment, and waste stabilization. While some studies have investigated its durability through accelerated tests, observing its aging over 15 years is essential for its commercial use and field deployment. The specimens were prepared from kaolinite, silica sand, sodium hydroxide, and water. The mixture was molded, compacted, and cured at 80 °C for 24 h to produce a stable geopolymer. Some samples were stored under ambient conditions, while others were immersed; both groups were left for 15 years. After this period, tests evaluated their mechanical, physical, and microstructural properties using XRD, EDS, and SEM. The samples stored under ambient conditions exhibited properties comparable to those of the unaged specimens. In contrast, the immersed samples were unstable, experienced mass loss, showed a sharp decline in strength, and displayed significant microstructural and phase changes. This study suggests adding an extra curing step, such as steaming (hydrothermal) or immersion in alkaline solutions, to enhance the long-term stability of geopolymer binder under immersion conditions. Full article

Currently, construction uses a vast array of materials that, while serving the same purpose, differ only slightly in their properties. This complicates the substitution of one material for another, significantly expanding the product range when considering operating conditions, necessitating expanded warehouse space. Therefore, preference should be given to universal materials that, while maintaining the same chemical composition, can change their properties by altering the ratio of their components. This study addresses this issue by evaluating the potential of glass composites containing powdered waste glass as alternatives to selected conventional construction materials. The results demonstrated that the rheological properties of the composites can be effectively controlled by adjusting the ratio of water glass to waste glass powder, enabling the achievement of viscosity values suitable for both plastering and installation mortars. In addition, the composites exhibited markedly higher adhesion strength than conventional gypsum mortars under high-humidity conditions, confirming their applicability as adaptable, substrate-specific materials with geopolymer-like characteristics. Full article

Geopolymer gel concrete (GPC) is a kind of environmentally friendly concrete, which has become a potential alternative material to replace ordinary concrete. Traditional mix design of GPC is carried out under experimental conditions, which is time-consuming and labor-intensive. Geopolymer concrete (GPC) is intended for use in hydraulic structures, which are often exposed to water environments. Water flow exerts significant abrasion and erosion on these structures. If the abrasion resistance (AR) of the material is poor, the service life and service quality of hydraulic structures will be substantially reduced under the action of water flow. Therefore, AR is a key performance indicator for GPC in hydraulic engineering applications. This abrasion resistance can be enhanced by using fibers (for example, steel fibers, polyvinyl alcohol (PVA) fibers, and basalt fibers) and nanomaterials. Furthermore, there is a complex nonlinear relationship between the proportions of fibers and nanoparticles added and the properties of GPC. In this study, the circular ring test method and the underwater steel ball test method were conducted to investigate the AR of nano-SiO₂ (NS) and hybrid fiber (NHF) reinforced geopolymer gel concrete (NHF-GPC). A backpropagation (BP) neural network (BPNN) model optimized by the Grey Wolf Optimizer (GWO) (GWO-BPNN) is established to predict the abrasion resistance strength (ARS) and the abrasion rate of NHF-GPC based on the circular ring test method. In addition, the ARS, abrasion rate, and average abrasion depth (AAD) based on the underwater steel ball test method were also predicted. The results indicate that the GWO-BPNN model demonstrates superior performance over the standard BPNN, exhibiting higher prediction accuracy, better fitting performance, and faster convergence speed. Specifically, for the circular ring test method abrasion rate prediction, GWO-BPNN reduced the root mean square error (RMSE) by 30.3% and lowered the mean absolute percentage error (MAPE) to 8.4%. The GWO-BPNN model established in this study can provide efficient and reliable theoretical support for the optimization of the NHF-GPC mix design. Full article

This study investigates the mechanical performance, high-temperature resistance, and microstructural characteristics of ground granulated blast furnace slag (GGBFS)-based geopolymer composites reinforced with boron nitride (BN)-modified hemp nanofibers. BN-modified hemp nanofibers (PVA-mBN/Hemp) were produced via electrospinning and incorporated into geopolymer mixtures at varying ratios ranging from 0 to 4 wt%. The effects of nanofiber content on composite properties were evaluated through mechanical testing, ultrasonic pulse velocity (UPV) measurements, and exposure to elevated temperatures (300–1200 °C), supported by SEM-EDS, FTIR, and XRD analyses. The results indicate that low nanofiber additions (0.5–1 wt%) improve flexural strength by up to 15%, although compressive strength is slightly reduced due to increased porosity. UPV measurements confirm the changes in internal structure. At elevated temperatures, nanofiber-reinforced samples exhibit enhanced residual strength compared to the control specimens, particularly at moderate temperatures, whereas significant degradation occurs above 900 °C. Microstructural analyses reveal improved fiber-matrix interaction, reduced crack propagation, and enhanced thermal stability attributed to BN modification. Overall, the incorporation of 0.5–1 wt% BN-modified hemp nanofibers provides an effective balance between mechanical performance and high-temperature resistance, highlighting their potential for use in sustainable and fire-resistant construction materials. This study contributes to the United Nations Sustainable Development Goals (SDGs), particularly SDG 9 (Industry, Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities), and SDG 12 (Responsible Consumption and Production). Full article