Search Results (72)

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

Certain clayey soils are susceptible to swelling and shrinkage due to moisture variations, which can lead to ground deformation and structural damage. Although traditional stabilization methods using lime and cement are effective, they involve high energy consumption and significant CO₂ emissions. In response to sustainability concerns, this study investigates the potential of in situ geopolymer stabilization of clay soils using industrial by-products as eco-friendly binders. Experimental studies were conducted on clay specimens stabilized with geopolymer binders produced from fly ash and waste brick powder activated by alkaline solutions. The selected clay exhibited stiff to very stiff behavior and was used as a reference material to ensure reliable evaluation without the influence of severe initial degradation. Reference samples with identical water content but without alkaline activation were also prepared. The primary objective was to assess geopolymers as a sustainable alternative to conventional binders, focusing on moisture sensitivity and long-term mechanical performance. Laboratory strength tests demonstrated that geopolymer-treated specimens exhibited significantly higher strength compared to untreated samples, indicating substantial improvement in engineering properties. Furthermore, Scanning Electron Microscopy (SEM) analyses revealed that the combination of dual activators (NS+NH) and thermal curing at 85 °C transformed the weak clay matrix into a dense, fibrous geopolymer network. However, the high curing temperature was primarily used to study the reaction mechanisms; the practical applicability of the method should be evaluated based on results obtained at ambient temperature. This structure enhanced particle bonding and mechanical interlocking by filling voids within the matrix. Overall, the findings confirm that geopolymer stabilization using industrial waste materials is an effective and environmentally sustainable alternative to conventional soil stabilization techniques, contributing to reduced carbon emissions in geotechnical engineering. Full article

The conservation of tuff- and coral rock-built architectural heritage structures (AHS) is challenging because access to original tuff and coral rock has become difficult and severely limited due to urbanization, land reclamation, the depletion of stone quarries, anti-mining and anti-quarrying legislation. An emerging approach to address this issue is to create compatible “replacement” rocks via geopolymerization, a process that is more sustainable and greener than the use of conventional cement and concrete. To explore the potential of geopolymers for AHS conservation strategies, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were implemented; 103 eligible articles were identified and classified into geopolymers for AHS (34 articles), tuff-built AHS (60 articles), and coral rock-built AHS (9 articles). Tuff substrates in AHSs appear in a variety of colors (yellowish-brown, grayish-cream, reddish-brown, pale greenish-gray and pink hues), densities (1.0–2.5 g/m³), and compressive strengths (3–100 MPa). Meanwhile, coral rock substrates in AHSs appear in whitish-cream color and are coarse-pored (1–5 MPa), fine-grained (8–15 MPa), and calcarenite (50–60 MPa). In terms of geopolymer formulation, metakaolin was reported as the most popular main precursor or admixture, while NaOH and Na₂SiO₃ were used simultaneously as alkaline activators. Aggregates used in geopolymer formulations depended on local availability, including quartz sand, river sand, crushed stones, carbonate stones, volcanic rock, volcanic sand, tuff, brick, ceramic tiles, and waste materials. Aesthetics, chemical composition, physical attributes, and mechanical properties have been identified as key criteria to ensure geopolymer compatibility for AHS conservation application. To date, geopolymers have been applied for AHS conservation as repair mortars, consolidants (i.e., grout and adhesives), and masonry strengthening (i.e., fiber-reinforced mortar). Finally, geopolymers formulated for AHS conservation have similar durability as the original substrate based on accelerated aging tests (i.e., salt mist, wet-dry, and freeze–thaw) and long-term outdoor exposure experiments. Full article

Masonry bricks and blocks are among the most widely used construction materials worldwide; however, their conventional production relies on energy-intensive firing processes and virgin raw materials, leading to significant environmental impacts. In response to increasing sustainability and decarbonization demands in the construction sector, numerous novel ceramic and refractory materials have been proposed for masonry applications. This systematic review provides a comprehensive assessment of recent advances in ceramic and refractory materials for masonry bricks and blocks, focusing on material classification, processing routes, microstructure–property relationships, and sustainability performance. Following the PRISMA 2020 guidelines, the peer-reviewed literature published between 2018 and 2025 was systematically identified, screened, and analyzed. An analytical framework based on well-established relationships from ceramic science was adopted to support consistent comparison of mechanical, thermal, acoustic, durability, and sustainability-related properties across heterogeneous material systems. Conventional fired ceramics, waste-derived ceramics, lightweight and porous systems, alkali-activated and unfired materials, and advanced engineered ceramics were comparatively evaluated. The results reveal a clear shift from dense traditional fired ceramics toward materials incorporating industrial and agricultural residues, engineered porosity, and low-temperature or unfired processing routes. Waste-derived and geopolymer-based systems demonstrate significant potential for reducing CO₂ emissions and energy consumption while maintaining functional performance suitable for masonry applications. Lightweight and porous ceramics exhibit enhanced thermal and acoustic behavior, often accompanied by reduced mechanical strength, highlighting application-dependent trade-offs. Overall, this review provides an integrated perspective linking composition, processing, microstructure, performance, and environmental impact, identifying key research trends and knowledge gaps relevant to sustainable masonry construction. Full article

This study investigates the feasibility of using brick and ceramic tile waste as aluminosilicate precursors for geopolymer synthesis by analyzing the influence of NaOH concentrations, the Na₂SiO₃/NaOH ratio, and curing methods on the physical and mechanical properties of the resulting matrices. Geopolymer pastes were prepared using NaOH concentrations ranging from 5 to 12 mol/L and Na₂SiO₃/NaOH ratios of 2:1 and 2.5:1. Compressive strength, water absorption, density, and void ratio were evaluated. The results indicate that a combined curing method, consisting of initial curing under dry ambient conditions followed by thermal curing at 60 °C, significantly improved the development of mechanical strength. The brick-based geopolymers reached maximum compressive strengths exceeding 55 MPa at intermediate NaOH concentrations, whereas ceramic tile-based geopolymers required higher alkalinity levels and increased soluble silica content. Overall, the findings confirm that an appropriate combination of precursor type, alkaline activator dosage, and curing conditions enables the formation of geopolymers with denser matrices and enhanced mechanical and physical properties, thereby supporting their potential as a sustainable alternative for the construction industry. Full article

In order to realize the large-scale resource utilization of solid waste in building materials, geopolymer mortar was prepared by alkali excitation technology with municipal solid waste incineration fly ash (MSWIFA), waste glass powder (WGP) and metakaolin (MK) as raw materials. After 28 days of curing, compressive strength and heavy metal leaching concentration of MSWIFA-WGP-MK geopolymer mortar were measured. The microstructure and phase composition of geopolymer samples were examined using scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analysis. The results demonstrated that the compressive strength of mortar increased as the MSWIFA content decreased and the alkali activator (AA) content increased. The mortar containing 30% MSWIFA and 35% AA achieved the highest 28-day compressive strength of 70.9 MPa. The high compressive strength was strongly associated with the compact microstructure, as revealed through scanning electron microscopy. The heavy metals in MSWIFA were solidified well in geopolymer matrix, and the leaching concentrations of heavy metals were below the regulatory thresholds. Based on the test results of mortars, concrete pavement bricks were produced. The performance of the optimized concrete paving brick satisfied requirements of the specification. The results indicated that the MSWIFA and WGP can be utilized in building materials. Full article

Synthetic microfibres released during textile drying are considered an emerging source of microplastic pollution, yet this waste stream is generally discarded without treatment. This study investigates a valorisation route by incorporating waste dryer-filter microfibres into a potassium-based/metakaolin geopolymeric coating for architectural applications, with the dual objective of preventing environmental release and enhancing material performance. Geopolymer pastes containing 0.1–0.3 wt.% of synthetic microfibres were characterised in terms of physical, mechanical and microstructural behaviour. Microfibre addition produced a marked toughening effect, with flexural strength increasing from about 3 MPa for the unreinforced matrix to 7.5 MPa for the composite containing 0.3 wt.% fibres, while compressive strength decreased moderately due to the presence of a compliant fibrous phase. Microstructural observations confirmed fibre dispersion and fibre–matrix bonding, supporting crack-bridging mechanisms. Density, porosity and water absorption measurements indicated a stable geopolymer gel structure with a connected pore network. Thin-layer applications onto clay brick exhibited satisfactory workability and adhesion, confirmed by pull-off testing (~0.12 MPa) and interfacial microscopy. The results demonstrate that textile-derived microfibres can be effectively immobilised within a potassium geopolymer matrix while improving flexural performance, offering a feasible circular strategy for microfibre waste reuse in mineral coatings. Full article

Valorizing construction and demolition waste (CDW) via alkaline activation enables low-carbon binders. This study assesses binary geopolymers formulated with recycled brick powder (PLR) and recycled concrete powder (PCR) in seven precursor ratios (0–100% PCR), activated with a ternary NaOH/Na₂SiO₃/KOH solution (silicate modulus M_s ≈ 3.2) at L/B = 0.15, and cured for 7, 14, and 28 days. Compressive strength (fc), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) were used to link microstructure–phases–properties. A local maximum in fc at ~30% PCR (16.2 MPa at 28 d) was observed versus 0% PCR (14.2 MPa) and ≥50% PCR (13.8 → 10.1 MPa at 28 d). XRD indicated a reduction in inherited crystalline phases and an increased amorphous fraction at ~30% PCR; FTIR (normalized peak position and FWHM of the T–O–Si band, not absolute intensity) suggested higher network extension; SEM-EDS (local/semiquantitative) showed a moderate rise in Ca that supports C-A-S-H domains bridging the N-A-S-H network. At a high PCR, excess Ca simplified mineralogy (quartz/portlandite dominance), promoted competitive routes (C-S-H/carbonation), reintroduced microdefects, and reduced fc. A theoretical oxide balance per mix identified a compositional window where Ca/(Si + Al) ≈ 0.35–0.45 coincides with the mechanical optimum and with XRD/FTIR tracers. Overall, a ~30% PCR window maximizes co-reticulation of N-A-S-H/C-A-S-H and densification without compromising aluminosilicate continuity, providing transferrable design and process-control criteria for CDW-based geopolymer binders. Full article

Geopolymer mortars were produced from construction and demolition waste using a binary binder of recycled brick powder/recycled concrete powder (RBP/RCP = 70/30 wt%), activated with a hybrid alkaline solution (NaOH/Na₂SiO₃/KOH) and reinforced with sisal fibres at 0–2 wt%. Mechanical performance (compression and three-point bending) and microstructure–phase evolution (XRD, FTIR, SEM-EDS) were assessed after low-temperature curing. Sisal addition delivered a strength–toughness trade-off with a reproducible optimum at ~1.0–1.5 wt%; at 2.0 wt%, fibre clustering and connected porosity reduced the effective load-bearing section, penalising flexure more than compression. Microstructural evidence indicates coexistence and co-crosslinking of N-A-S-H and C-(A)-S-H gels—enabled by Ca from RCP—leading to matrix densification and improved fibre–matrix anchorage. Fractographic features (tortuous crack paths, bridging, and extensive pull-out at ~1.5 wt%) are consistent with an extended post-peak response and higher fracture work without compromising early-age strength. This study achieves the following: (i) it identifies a practical reinforcement window for sisal in RBP/RCP geopolymers, (ii) it links gel chemistry and interfacial phenomena to macroscopic behaviour, and (iii) it distils processing guidelines (gradual addition, workability control, gentle deaeration, and constant A/S) that support reproducibility. These outcomes provide a replicable, low-embodied-CO₂ route to fibre-reinforced geopolymer mortars derived from CDW for non-structural and semi-structural applications where flexural performance and post-peak behaviour are critical. Full article

Kiln-fired clay bricks are energy-intensive and carbon-heavy. This study develops and validates kiln-free, pressure-free, and ambient-cured geopolymer (GPM) bricks made from uncalcined clay and Class F fly ash. A two-stage experimental program screened 33 mixes (12–16 M NaOH and 396 cubes tested at 14–90 days) and then scaled six optimized mixes to 90 full-size bricks for mechanical, durability, and microstructural evaluation. Bricks with an optimal mix of 20–30% clay and 70–80% fly ash achieved a compressive strength of up to 32.5 MPa, satisfying ASTM C62 (for severe weathering) requirements. Relative to fired clay units, GPM bricks delivered +61% average compressive strength (up to +91%), +56.5% average modulus of rupture (up to +103%), 6–29% lower water absorption, and 42–84% higher UPV while their strength losses after 28-day immersion in 5% H₂SO₄ or 3.5% NaCl were only ~3–5%. SEM confirmed a dense N-A-S-H gel matrix with reduced porosity. Eco-efficiency analysis showed ~95% lower embodied CO₂ (0.26–0.31 vs. 5.5 kg eCO₂ per brick) and ~35% lower cost per MPa of strength than fired clay bricks. The findings demonstrate a practical, low-carbon brick manufactured without mechanical pressing or heat curing, delivering verified performance and durability under ambient conditions. Full article

Refractory geopolymers derived from aluminosilicate sources and alkaline activation are a promising alternative to traditional fired bricks, particularly when low-cost, waste-derived raw materials are used. This study improves the workability of a refractory brick formulated with clays (Kaolin and Tepozan–Bauwer), seashell waste, sodium silicate, potassium hydroxide, and water by incorporating sodium lignosulfonate (LS) and polycarboxylate (PC) plasticizers. Clays from Comonfort, Guanajuato, Mexico, and seashells were ground and sieved to pass a 100 Tyler mesh. A base mixture was prepared and evaluated using the Mini Slump Test, varying plasticizer content from 0 to 2% relative to the solid fraction. Based on workability, 0.5% LS and 1% PC (by solids) increased the slump, and a blended plasticizer formulation (1.5% by solids, 80%PC+20%LS) produced the highest workability. These additives act through different mechanisms, with LS primarily promoting electrostatic repulsion and PC steric repulsion. Bricks with and without plasticizers exhibited thermal resistance up to 1200 °C. After four calcination cycles, compressive strength values were 354.74 kg_f/cm² for the brick without plasticizer, 597.25 kg_f/cm² for 1% PC, 433.63 kg_f/cm² for 0.5% LS, and 519.05 kg_f/cm² for 1.5% of the 80%PC+20%LS blend. Strength was consistent with changes in porosity and apparent density, and 1% PC provided a favorable combination of high workability and high compressive strength after cycling. Because the cost of clays and seashells is negligible, formulation selection was based on plasticizer cost per brick. Although 1% PC and the 1.5% of 80%PC+20%LS blend showed statistically comparable strength after cycling, 1% PC was selected as the preferred option due to its lower additive cost ($0.0449 per brick) compared with the blend ($0.0633 per brick). Stereoscopic microscopy indicated pore closure after calcination with no visible cracking, and SEM–EDS identified O, Si, and Al as the significant elements, with traces of S and K. Overall, the study provides an integrated assessment of workability, multi-cycle calcination, microstructure, and performance for refractory bricks produced from readily available clays and seashell waste. Full article

The disposal of industrial waste poses a significant environmental challenge, often leading to pollution and degradation of surrounding and terrestrial ecosystems. This study investigates the sustainable valorization of such wastes through the development of one-part geopolymer mortars. Solid sodium silicate was employed as a dry alkali activator for binary blends comprising ground granulated blast-furnace slag (GGBS), clay brick powder (CBP), steel slag (SS), and fly ash (FA), with all mixtures cured under ambient conditions. The mortars were evaluated in terms of fresh properties (flow and setting time) and hardened characteristics, including compressive strength, density, water absorption, and porosity. Durability performance was assessed through mass loss, visual degradation, and compressive strength retention following exposure to acidic (H₂SO₄, HCl) and sulfate environments. Microstructural characterization using XRD, SEM, and FTIR provided insight into the mechanisms of gel formation and degradation in aggressive media. The results revealed that incorporating 5% FA into GGBS-based mortars enhanced 28-day compressive strength by 21.7% compared with the control mix. The inclusion of industrial by-products promoted the formation of C–S–H and C–(A)–S–H gels, contributing to a denser and more refined microstructure. Overall, the findings demonstrate that one-part geopolymer mortars offer a promising, eco-efficient, and durable alternative to traditional cementitious systems, while also addressing safety and handling concerns associated with liquid alkaline activators used in conventional two-part geopolymer formulations. Full article

Utilizing waste red-clay brick powder (WRCBP) as a precursor for manufacturing geopolymers is increasingly popular due to its environmental and economic benefits. However, the geopolymerization of this waste remains insufficiently explored. This study evaluates the differences in physical–mechanical properties and microstructural evolution of WRCBP- and fly ash (FA)-based geopolymers to determine the reactivity of WRCBP. Mineral admixtures, including granulated blast furnace slag (GF) and metakaolin (MT), were incorporated with WRCBP to fabricate geopolymer pastes, while FA was used in parallel for comparison. The effects of activator modulus (1.2 and 1.4 for Na₂SiO₃) and curing conditions (65 °C and 90 °C) on the mechanical and microstructural performance of the prepared pastes were investigated through water demand analysis, compressive strength testing, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The results indicate that WRCBP-based pastes achieved a comparable compressive strength (39.8 MPa) under appropriate alkali-activated and curing conditions relative to FA-based pastes (42.5 MPa). The modulus of the alkaline activator exerted a greater influence on strength development than the raw material composition. For both WRCBP- and FA-based pastes, 65 °C was identified as a more suitable curing temperature. Moreover, compared with FA-based pastes, pastes produced using WRCBP provide enhanced social and economic benefits. Overall, this study confirms that high-performance binders can be engineered by incorporating WRCBP, thereby supporting the development of sustainable low-carbon construction materials. Full article

The construction industry’s growth is causing a surge in CO₂ emissions, driven by increased demand for concrete and other building materials. There is a growing demand for more sustainable building materials, including alkali-activated materials. This study investigates the impact of varying ratios of Na₂SiO₃ and NaOH on the mechanical properties and microstructure of metakaolin (MKW) and ceramic brick waste (CBW) based geopolymer binder. Geopolymer binder precursors were made of three main CBW/MKW ratios: 100/0%wt. (C100), 50/50%wt. (C50M50), and 0/100%wt. (M100). Alkaline activator solutions had three different Na₂SiO₃/NaOH ratios: 0.5, 1.0, and 2.0. The investigation into the geopolymer binder mechanical properties was conducted using a range of analytical methods, including compressive strength, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The findings of the study indicate that the Na₂SiO₃/NaOH ratio alone is inadequate for evaluating geopolymer mechanical properties when different AS/P ratios are employed, given its influence on other parameters, such as the W/S ratio and the total Na₂O content. CBW-based geopolymer binders demonstrate limited capacity to attain substantial compressive strengths because they contain high amounts of unreacted CBW particles, as shown by XRD analysis. The incorporation of MKW precursor resulted in enhanced reactivity and intensified geopolymerization reaction. After the evaluation of all essential ratios, the most favorable Na₂SiO₃/NaOH ratio is 1.0. This determination was based on the highest strengths observed in designs that contained ≥50% of MKW precursor, attributed to predominance of goosecreekite and N-A-S-H gels, as evidenced by XRD and FT-IR analysis. Full article

This study investigates the effects of varying filler content on the thermal and mechanical performance of metakaolinite-based geopolymer composites designed for thermal energy storage applications. The composites were formulated using a geopolymer binder, combined with a thermally stable filler (ground chamotte) and a thermal energy storage filler (waste steel chips) in different proportions. Chamotte content within the binder matrix (binder + chamotte) ranged from 20 to 40 wt.%, while steel chip content varied from 0 to 40 wt.% of the total composite mass. The thermal properties of the composites were evaluated at room temperature and compared with conventional reference materials, including Ultraboard, chamotte brick, and magnetite brick. Mechanical performance, specifically flexural and compressive strength, was evaluated at room temperature and after exposure to elevated temperatures (800 and 1100 °C), followed by two cooling regimes, slow furnace cooling and rapid water quenching. Microstructural characterization via optical microscopy was used to examine filler dispersion and matrix–filler interactions. The results showed that the thermal effusivity of the optimized composites exceeded that of chamotte brick by more than 50%. The highest flexural (12.68 MPa) and compressive (86.18 MPa) strengths were achieved in the composite containing 20 wt.% steel chips, prior to thermal exposure. Microstructural observations revealed the diverse geometry of the steel chips and arrangement of the chamotte particles. These findings highlight the potential of incorporating metallic waste materials into geopolymer systems to develop multifunctional composites with improved thermal storage capacity and mechanical resilience. Full article