The study, published in Frontiers in Built Environment, systematically combined two treatments that had previously only been explored separately: doping the clay with industrial metal oxides and chemically activating the mixture with an alkaline solution. The researchers, led by Hebah Mohammad Al-Jabali of Yarmouk University, prepared bricks from a base recipe of 82 percent clay, 13 percent fine sand, and 5 percent Class F fly ash, then added varying doses of iron oxide (Fe2O3), aluminum oxide (Al2O3), or carbon black N550. Some batches were left untreated, while others were mixed with an alkaline activator solution of 8 molar sodium hydroxide combined with sodium silicate.

The chemistry behind the improvement is geopolymerization. Hydroxide ions from the sodium hydroxide dissolve aluminosilicate species from the clay and fly ash, and those dissolved species then polymerize into a three-dimensional amorphous gel known as N-A-S-H — a sodium aluminosilicate hydrate. This gel coats unreacted particles, fills pores, and binds the whole matrix together. The metal oxides add a second layer of benefit: dissolved aluminum and iron ions substitute into the gel structure, and fine oxide particles act as nucleation sites and packing fillers that refine the pore network.

The standout performer was the mixture labeled Al-7A, containing 7 percent alumina by clay weight plus alkali activation. At room temperature it reached a compressive strength of 19.5 megapascals, a 57.3 percent increase over the untreated control’s 12.4 megapascals. More remarkably, after two hours of exposure to 800 degrees Celsius in a muffle furnace, the same mixture retained 14.8 megapascals — 75.9 percent of its original strength. Conventional fired clay bricks typically retain only 48 to 91 percent of their strength under comparable conditions, and the untreated control in this study fell to just 6.1 megapascals after the same thermal assault.

The iron oxide and carbon black variants also benefited from activation, though less dramatically. The Fe-4A mixture, with 4 percent iron oxide, achieved 16.8 megapascals at ambient temperature and 11.5 megapascals after 800-degree exposure, while the CB-0.5A mixture with 0.5 percent carbon black reached 16.0 and 10.5 megapascals respectively. Iron oxide acts as a flux, promoting liquid-phase sintering that densifies the ceramic body, but beyond about 5 percent the excess liquid phase becomes detrimental — a dose-dependence the team documented clearly. Carbon black works differently: it burns out during heating, leaving behind a controlled porous structure that improves thermal insulation at some cost to strength.

The temperature trajectory of brick behavior follows a well-understood mineralogical script. Around 200 degrees Celsius, physically bound water evaporates, and most specimens actually gained a few percent in strength as the matrix compacted. At 400 degrees, kaolinite undergoes dehydroxylation, converting to metakaolin and sacrificing some strength. Near 573 degrees, the alpha-to-beta quartz transition causes volume expansion and microcracking, driving further losses. Above 800 degrees, metakaolin begins transforming into spinel and mullite — crystalline phases that can restore strength at even higher temperatures. The alkali-activated bricks appear to accelerate this ceramic bonding, forming thermally stable crystalline phases within the gel matrix.

Durability metrics reinforced the mechanical story. The Al-7A mixture absorbed only 8.8 percent water by mass, 38 percent lower than the control’s 14.2 percent, and achieved a bulk density of 1,980 kilograms per cubic meter. Thermogravimetric analysis showed Al-7A lost just 4.8 percent of its mass up to 800 degrees, retaining 95.2 percent — the best thermal stability of any formulation. Scanning electron microscopy revealed the reason: the control bricks showed loose, cracked particles with large intergranular voids, while the activated mixtures displayed a continuous gel matrix enveloping the particles, with Al-7A exhibiting the densest, most homogeneous microstructure of all.

Accelerated aging tests added a practical dimension. The team subjected the best-performing mixtures to seven cycles of five-hour water soaking followed by 42-hour drying at 70 degrees Celsius, mimicking years of moisture cycling. The control lost 37.1 percent of its strength, but Al-7A retained 82.1 percent of its initial value, with Fe-4A at 75.0 percent and CB-0.5A at 70.6 percent. The dense geopolymer matrix limits water ingress during wetting, reducing the internal pressures that drive microcracking in conventional bricks.

The environmental implications are significant. Because alkali-activated bricks cure at modest temperatures rather than requiring energy-intensive kiln firing, the approach could cut the substantial carbon footprint of the roughly 1.39 trillion bricks produced worldwide each year. The researchers note that the technique uses locally available clay and industrial additives, and that the resulting material could serve not only in fire-prone buildings but also in heat-resistant structures such as heat-exchanger linings. Buildings currently lose roughly half of the one-third of global energy they consume through poorly insulating envelopes, so any material that improves both fire resilience and thermal performance addresses two problems at once.

The authors caution that some conclusions remain provisional: the suspected formation of mullite and spinel phases was inferred from behavior and microscopy rather than direct X-ray diffraction confirmation, and thermal conductivity was not directly measured on the carbon black formulations. Future work, they say, should include those measurements. Still, the demonstration that a simple combination of alumina powder and sodium hydroxide activation can nearly double the post-fire strength of clay brick marks a striking convergence of ancient material and modern chemistry — one that could reshape how the world’s most common building unit survives its hottest moments.

Subject of Research: Alkali-activated clay bricks with metal oxide additives for enhanced residual strength at elevated temperatures

Article Title: Enhancing the residual strength of clay bricks exposed to elevated temperatures using metal oxides, carbon black, and sodium hydroxide activation

Article References: Al-Jabali, H. M., Edris, W. F., Abdelkhalik, A., Al-Kader A. Al Sayed, A., & Khairy, S. (2026). Enhancing the residual strength of clay bricks exposed to elevated temperatures using metal oxides, carbon black, and sodium hydroxide activation. Frontiers in Built Environment, 12, Article 1966926. https://doi.org/10.3389/fbuil.2026.1966926

Image Credits: AI Generated

DOI: 10.3389/fbuil.2026.1966926

Keywords: materials science, clay bricks, alkali activation, geopolymer, fire resistance, construction materials, alumina, thermal stability, Enhancing, residual, strength, clay

The choice of an L16 orthogonal array is central to the efficiency of the experimental program. Orthogonal designs, rooted in the work of Genichi Taguchi and classical factorial design theory, allow the independent estimation of main effects for multiple factors using a fraction of the full factorial run count. With five mix parameters under investigation—slag content, metakaolin content, sodium hydroxide molarity, the sodium silicate to sodium hydroxide ratio, and the alkali-to-binder ratio—a full factorial exploration at even modest resolution would require dozens to hundreds of paste batches. The L16 array compresses this into sixteen carefully balanced runs in which each factor level appears an equal number of times and factor levels are distributed orthogonally across columns. This balance means that, on average, the influence of one factor is not confounded with the linear influence of another, enabling analysis of variance to attribute portions of observed variance to individual parameters. The trade-off, as the authors themselves note, is that certain two-factor interactions cannot be fully disentangled from main effects within a resolution-limited array, a limitation that is well understood in design-of-experiments practice and typically addressed through follow-up experiments at the identified optimum.

The finding that the alkaline activator ratio exerted the greatest influence on compressive strength aligns with the fundamental chemistry of geopolymerisation. The sodium silicate to sodium hydroxide ratio controls the availability of dissolved silica in the activating solution, which in turn governs the Si/Al ratio of the forming gel network. Higher soluble silica content generally promotes denser, more cross-linked aluminosilicate gels and, in calcium-rich systems, modifies the composition of C-(A)-S-H phases toward higher chain length and greater mechanical integrity. Dissolved silica also moderates the highly caustic environment of sodium hydroxide, affecting the rate at which precursor particles dissolve and the degree to which dissolved species polycondense into stable networks. Meanwhile, the identification of the alkali-to-binder ratio as the dominant factor for flowability is consistent with rheological behavior in alkaline-activated pastes: the total volume of liquid relative to solid determines the spacing between particles and the viscosity of the suspending medium, and alkaline activator solutions are substantially more viscous than water, amplifying their effect on workability.

The economic dimension of the optimization deserves particular attention because it is frequently neglected in laboratory studies of alternative binders. Metakaolin, produced by calcining kaolinitic clay at moderate temperatures, carries an embodied energy cost and a market price considerably higher than that of fly ash or slag, which are industrial byproducts available at low cost near their points of generation. The study’s identification of metakaolin dosage as the dominant contributor to material cost therefore has direct practical consequences: even modest increases in metakaolin content can shift the economics of a mix substantially, which is why the optimal formulation converged on a low metakaolin fraction of ten percent. This cost sensitivity also highlights a general principle in sustainable materials engineering—the environmental and economic benefits of byproduct utilization depend heavily on local supply chains, transport distances, and competing demands for the same materials from other industries, factors that a laboratory cost model can only approximate.

The curing regime established in the preliminary single-factor experiments also merits scientific context. Geopolymerisation is a thermally activated dissolution-condensation process, and low-calcium fly ash systems in particular require elevated temperatures to achieve meaningful reaction within practical timeframes. Temperatures in the range of 60 to 80 degrees Celsius are commonly reported as favorable for fly ash activation, with the 60 degrees Celsius, 24-hour condition identified here as optimal balancing reaction extent against the risk of excessive water loss or gel coarsening at higher temperatures. The presence of slag in the ternary system partially relaxes this thermal requirement, since calcium-rich systems gain strength appreciably at ambient temperature, but heat curing remains beneficial for achieving early strength in blended systems. This thermal dependence has implications for field application, where ambient-temperature curing or modest heat treatment would be required, and it represents one of the practical hurdles that distinguishes geopolymer concretes from conventional Portland cement systems in cold-weather construction.

The microstructural observations reported through X-ray diffraction and scanning electron microscopy provide the mechanistic underpinning for the mechanical results. X-ray diffraction in geopolymer systems typically reveals the characteristic broad hump associated with short-range ordered aluminosilicate gel, superimposed on residual crystalline phases such as quartz and mullite inherited from the fly ash. Shifts in the position of this hump and changes in its relative intensity reflect alterations in gel composition and quantity. Scanning electron microscopy, in turn, allows direct visualization of gel morphology, unreacted particle remnants, and the pore network. The reported features of enhanced C-(A)-S-H and N-A-S-H gel formation, increased matrix densification, and reduced porosity in the optimized mixtures are exactly what reaction mechanism models would predict for a well-balanced ternary system: slag-derived calcium gel fills space and provides early binding, while fly ash and metakaolin-derived sodium aluminosilicate gel contributes to long-term framework development, and the coexistence of the two gel types in an intermixed morphology is widely associated with superior mechanical performance in hybrid systems.

The statistical methodology underlying the decision model also reflects current best practice in multi-criteria optimization. Entropy weighting is an objective technique that assigns greater weight to criteria exhibiting greater variability across the experimental alternatives, on the reasoning that a parameter that discriminates strongly between options carries more information for decision-making. Combining this with subjective weighting, which encodes engineering judgment about the relative importance of strength, workability, and cost, produces a synthetic weighting scheme that tempers purely data-driven assignment with domain expertise. This hybrid approach guards against the failure modes of either extreme: purely subjective weights can be arbitrary and difficult to defend, while purely entropy-based weights can overemphasize criteria whose variability is an artifact of the chosen experimental levels rather than of genuine practical importance. The convergence of the multi-objective analysis on a mixture with moderate values of most parameters—fifty percent slag, ten percent metakaolin, six molar sodium hydroxide, an activator ratio of one to one point five, and an alkali-to-binder ratio of zero point three five—is characteristic of Pareto-optimal solutions in multi-objective problems, where the best compromise rarely coincides with the extreme values that maximize any single objective.

The reported maximum compressive strength of 115.87 megapascals under one experimental condition is notable in the context of published geopolymer literature, where ambient-cured fly ash systems typically achieve strengths in the range of 30 to 70 megapascals and heat-cured or slag-rich systems can exceed 100 megapascals. The high value is consistent with the combination of substantial slag content, heat curing, and an activator chemistry favoring dense gel formation. However, the authors’ transparency about the replication structure of their testing is scientifically important. The three compressive strength specimens per mixture were subsamples drawn from a single batch rather than products of independent batch preparations, which means that the reported variability reflects within-batch homogeneity rather than between-batch reproducibility. Between-batch variation, arising from differences in mixing efficiency, temperature, activator preparation, and precursor sampling, is typically larger than within-batch variation, so the true uncertainty surrounding each mixture’s mean strength is likely wider than the within-batch statistics alone would suggest. The observation that repeat testing broadly preserved the relative ranking of selected mixtures is reassuring for the optimization conclusion, since ranking-based decisions are more robust to absolute strength uncertainty than threshold-based ones, but independent replication at the batch level remains a desirable confirmation step.

From a sustainability perspective, the study contributes to a growing body of evidence that industrial byproducts can substitute for Portland cement clinker at high replacement levels without sacrificing mechanical performance. Cement production is estimated to account for roughly seven to eight percent of global carbon dioxide emissions, driven both by the calcination of limestone and by the fossil fuel energy consumed in clinker kilns. Geopolymer binders eliminate the calcination step entirely, and while the alkaline activators—particularly sodium silicate—carry their own embodied emissions, life cycle assessments generally report substantial net reductions for geopolymer concretes relative to ordinary Portland cement equivalents, with the magnitude depending on activator dosage and transport distances. Ternary systems that incorporate slag, itself a finite byproduct facing increasing demand, raise questions about long-term resource availability, which strengthens the case for including calcined clays such as metakaolin in precursor blends, since clay reserves are abundant and calcination can be performed at temperatures far below those required for clinker production.

The workability findings also carry practical significance for construction practice. Flowability, typically assessed in paste systems through mini-slump or flow table tests, serves as a proxy for the fresh-state behavior of the corresponding concrete, where workability governs placement, compaction, and finishability. The strong influence of the alkali-to-binder ratio on flowability identified in the effect analysis suggests that contractors seeking to adjust workability in the field would have a more effective lever in the liquid content than in the activator composition, though such adjustments must be balanced against the strength consequences of diluting the alkaline environment. The interplay between workability and strength is a recurring theme in geopolymer technology, and the multi-objective framework applied here offers a structured way to navigate it rather than relying on iterative trial and error, which the authors correctly identify as laborious and inefficient for multi-parameter systems.

Finally, the methodological integration demonstrated in this study—combining screening-level single-factor experiments, an orthogonal array for efficient multi-factor assessment, analysis of variance for effect attribution, and a hybrid weighted decision model for multi-objective selection—constitutes a transferable template for other researchers working on complex binder systems. The approach is not limited to geopolymers; it applies equally to alkali-activated materials, limestone calcined clay cements, and other multi-component systems where formulation space is large and performance criteria are competing. The explicit acknowledgment of limitations, including the interaction confounding inherent in the chosen array and the subsample nature of the mechanical replicates, models the kind of methodological candor that allows subsequent studies to build incrementally on reported results, refining the optimum through targeted confirmation experiments and extending the framework to durability indicators, long-term strength development, and full-scale concrete applications where aggregate packing and interfacial transition zone effects introduce additional layers of complexity.

Subject of Research: Optimization of a ternary geopolymer paste through orthogonal experimental design, ANOVA and entropy-based multi-objective decision analysis

Article Title: Optimization of a ternary geopolymer paste through orthogonal experimental design, ANOVA and entropy-based multi-objective decision analysis

Article References: Murugeswari, S., & Meena, T. (2026). Optimization of a ternary geopolymer paste through orthogonal experimental design, ANOVA and entropy-based multi-objective decision analysis. Frontiers in Built Environment, 12, Article 1934627. https://doi.org/10.3389/fbuil.2026.1934627

Image Credits: AI Generated

DOI: 10.3389/fbuil.2026.1934627

Keywords: geopolymer, fly ash, GGBS, metakaolin, orthogonal experimental design, ANOVA, entropy weighting, multi-objective optimization, compressive strength, sustainable construction, XRD, SEM

The researchers turned to rhyolitic tuff, a porous volcanic rock abundant in Anatolia, as the base material for a family of geopolymer tiles. Geopolymers are inorganic binders formed by activating aluminosilicate-rich raw materials with alkaline solutions, and unlike ordinary Portland cement, they can be produced without high-temperature clinkering, which makes them dramatically less carbon-intensive. By milling the tuff and blending it with micronized calcite, then adding variable amounts of zinc oxide powder and a small dose of conductive fibers, the team created tiles designed to serve as structural building elements and electromagnetic shields at the same time.

The experimental program was unusually thorough. The researchers measured water absorption and drying shrinkage, tested compressive and flexural strength according to standard ASTM procedures, examined the microstructure of the cured composites, and—most importantly—characterized electromagnetic shielding effectiveness across a sweep from 900 to 6000 MHz at 100 MHz intervals. They also performed life-cycle-style accounting of carbon dioxide emissions and production costs, benchmarking their best geo-tiles against conventional ceramic tiles, which are fired in energy-hungry kilns at temperatures exceeding 1000 degrees Celsius.

Zinc oxide emerged as the quiet workhorse of the mechanical side of the story. Incorporating the powder significantly enhanced the compressive and flexural performance of the tuff-based geopolymers, consistent with a growing body of literature showing that ZnO can refine pore structure and influence hydration and reaction kinetics in cementitious and alkali-activated systems. In other words, the additive did not just ride along—it actively strengthened the matrix, improving the durability characteristics that any real tile would need to survive in a building envelope.

But when it came to blocking electromagnetic waves, the type of fiber made all the difference. Each mix received the same total fiber dosage—two percent by volume—drawn from three candidate reinforcements: polypropylene fibers, brass-coated micro-steel fibers, and carbon fibers. The carbon fiber-reinforced geopolymers decisively outperformed the rest, posting total shielding values of 31.2 dB at 900 MHz, 42.8 dB at 1800 MHz, 39.16 dB at 2400 MHz, and 46.86 dB at 5000 MHz. For context, a shielding effectiveness of 40 dB means that only one ten-thousandth of the incident electromagnetic energy gets through, which is enough to meet most commercial shielding requirements for sensitive electronics.

The synergy between the functional powder and the conductive fibers proved even more striking. When the researchers combined 2.5 percent by volume of zinc oxide with 2 percent by volume of carbon fibers, the composite reached a total shielding effectiveness of 60.32 dB at 5800 MHz—a frequency band that sits squarely in the upper range used by modern 5G and Wi-Fi systems. At 60 dB, only one part in a million of the incoming radiation penetrates the tile, a level of attenuation that rivals purpose-built shielding enclosures. The mechanism is a classic one in shielding science: carbon fibers form interconnected conductive networks that reflect and dissipate incoming waves through induced currents, while the ZnO-modified matrix contributes dielectric loss and improves impedance matching so that more energy enters the material to be absorbed rather than bouncing off the surface.

The economic and environmental results may be the most viral-worthy part of the study. The lowest recorded carbon footprint among the developed geo-tiles was 2.63 kilograms of CO2 per square meter, and the lowest production cost came in at $1.30 per square meter. Compared with conventional ceramic tiles, that represents reductions of approximately 81.7 percent in CO2 emissions and 90.9 percent in cost. The savings stem from what the geopolymers avoid: no kiln firing at extreme temperatures, no energy-intensive clinker production, and a raw material—rhyolitic tuff—that is essentially a low-value volcanic byproduct of the landscape. The study was supported by the Scientific and Technological Research Council of Türkiye, and the steel fibers used in the experiments were supplied as waste material by Kardemir Steel Industry, adding a circular-economy dimension to the work.

Why does this matter beyond the laboratory? Modern buildings are being asked to serve as faraday-like refuges for a growing inventory of electromagnetic-dependent infrastructure: data centers, hospitals with sensitive imaging equipment, secure government facilities, and increasingly, ordinary homes where residents worry about interference between the dozens of wireless devices competing for spectrum. A tile that can be laid as a standard floor or wall finish—while passively attenuating signals across nearly the entire relevant frequency range—would eliminate the need for separate shielding layers, metal meshes, or costly retrofits. And because the material is a geopolymer rather than a fired ceramic, it aligns with the construction industry’s urgent push to decarbonize, given that cement and ceramic production together account for a substantial share of global industrial emissions.

Of course, translating laboratory results into building products involves hurdles. The durability of carbon fibers in the highly alkaline geopolymer environment over decades, the scaling of mixing procedures to industrial tile production, and long-term structural performance all warrant further study. The authors also note that fiber type played a pivotal role in determining shielding properties, meaning that material specification will need to balance mechanical demands, cost, and electromagnetic targets on a project-by-project basis. Steel fibers, for instance, offer magnetic loss mechanisms that carbon lacks, while polypropylene fibers contribute mainly to crack control rather than conductivity.

Still, the core finding stands as a compelling proof of concept: a humble volcanic rock, activated with alkalis, stiffened with zinc oxide, and threaded with carbon fibers, can be transformed into a multifunctional building tile that strengthens structures, shields electronics, slashes carbon emissions by more than 80 percent, and cuts costs by more than 90 percent relative to the ceramic tiles found in millions of kitchens and bathrooms. If future work confirms long-term durability, the walls and floors of tomorrow’s buildings may quietly become the electromagnetic shields that today’s infrastructure still builds as expensive afterthoughts.

Subject of Research: Electromagnetic shielding performance of fiber-reinforced rhyolitic tuff geopolymer tiles with zinc oxide

Article Title: Synergistic effects of carbon, steel, and polypropylene fibers with ZnO on the electromagnetic shielding of rhyolitic tuff geo-tile

Article References: Pekgöz, M., & Tekin, İ. (2026). Synergistic effects of carbon, steel, and polypropylene fibers with ZnO on the electromagnetic shielding of rhyolitic tuff geo-tile. Polymer Bulletin, 83(12), Article 686. https://doi.org/10.1007/s00289-026-06743-5

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06743-5

Keywords: geopolymer, rhyolitic tuff, electromagnetic shielding, carbon fiber, zinc oxide, steel fiber, polypropylene fiber, CO2 emissions, ceramic tile alternative, construction materials, 5G shielding, sustainable building

The material in question is concrete slurry waste, the alkaline sludge generated when truck mixers and batching plants are washed out at ready-mixed concrete facilities, along with the surplus concrete that comes back when suppliers overorder. Traditionally treated as a disposal headache because of its high pH, moisture content and inconsistent composition, this slurry actually contains residual unhydrated clinker minerals and cement hydration products. Earlier work by the same researcher demonstrated something remarkable: when the slurry water is subjected to pressurized wet carbonation with supercritical carbon dioxide, each kilogram of the resulting solid can lock away approximately 130 grams of CO2 in stable carbonate form. That turns a waste stream into a carbon sink, but the open question was whether the carbonated powder could do useful chemical work inside a geopolymer, or whether it would simply dilute the mixture.

Geopolymers are binders built not on Portland cement clinker but on aluminosilicate precursors such as fly ash, metakaolin or ground granulated blast-furnace slag, known as GGBS, which are dissolved and reassembled by a strongly alkaline activator solution. In slag-rich systems, the abundant calcium drives the formation of calcium-sodium aluminosilicate hydrate gels, abbreviated C-(N)-A-S-H, which knit into a dense load-bearing network remarkably quickly. The new research, conducted by Sangrak Sim, asked what happens when carbonated concrete slurry waste, or CCSW, replaces 25, 50 or 75 percent of the GGBS by mass in such a system, with the activator-to-binder ratio held constant at 0.6 and a fixed sodium silicate to sodium hydroxide solution ratio of 2.0.

The carbonation step itself proved transformative. Uncarbonated slurry waste showed pronounced X-ray diffraction peaks from anhydrous clinker phases and portlandite, the crystalline calcium hydroxide left over from hardened cement. After ten minutes in a pressurized reactor at 40 degrees Celsius and 100 bar of CO2, those peaks vanished and calcite dominated instead. Perhaps more surprisingly, the carbonation process also shattered the particles: the median particle diameter dropped from 8.89 micrometers for the raw waste to 7.48 micrometers for the carbonated product, with no grinding involved, because the fine calcium carbonate crystals formed during carbonation break the material apart. Fine particles pack better and dissolve faster, which matters enormously in a reactive binder.

The mechanical results traced a clear dose-response curve. The pure GGBS control paste reached compressive strengths of 46.7 megapascals after one day, 73.9 after seven and 87.9 after 28 days of humid curing. At a 25 percent replacement level, the carbonated waste paste was nearly indistinguishable at early ages, hitting 46.4 megapascals on day one and finishing at 81.9 megapascals after 28 days, only about 6 megapascals below the control. Doubling the replacement to 50 percent cost roughly 23 megapascals of 28-day strength, while at 75 percent the paste managed just 4.7 megapascals at one day and 43.1 at 28 days, with almost no strength gain in the final three weeks. The pattern points to dilution: every kilogram of waste displaces a kilogram of highly reactive slag, and calcite, whatever its virtues, cannot rebuild the gel network on its own.

Yet the spectroscopic evidence revealed that the waste is far from inert. Fourier-transform infrared spectroscopy, deconvoluted across the 800 to 1200 per centimeter window where silicon-oxygen-aluminum stretching vibrations live, allowed the researcher to calculate a degree of geopolymerization for each paste. The control climbed from 49.1 percent at one day to 72.8 percent at 28 days. The 25 percent blend reached 64.4 percent, the 50 percent blend 62.3 percent, and even the 75 percent blend managed 56.2 percent, all rising steadily with curing age. Meanwhile, the calcite-related peak area actually shrank over time in some blends, dropping from 3.05 to 2.43 in the 50 percent mixture between days one and 28. That decline hints that under the fierce alkalinity of the activator, calcite surfaces partially dissolve, releasing calcium ions that feed the surrounding gel chemistry rather than sitting passively in the matrix.

Thermogravimetric analysis reinforced this picture with quantitative mass-loss fingerprints. Carbonate decomposition losses at 28 days rose predictably with waste content, from 1.41 percent in the control to 5.44 percent in the 75 percent blend, confirming the calcite inventory. But the mass loss between 300 and 600 degrees Celsius, a region complicated by overlapping dehydroxylation of hydroxyl-bearing gels and the decomposition of poorly crystalline carbonate species, also increased with waste content at every age. Combined with scanning electron microscopy, which revealed two distinct gel chemistries around waste particles, a calcium-poor aluminosilicate gel formed from the waste’s amorphous phases and a calcium-rich gel nucleated near carbonate surfaces, the data sketch a material playing three roles at once: a partial reactive precursor, a fine filler, and a nucleation scaffold.

Pore structure measurements tied these chemical stories to physical performance. Mercury intrusion porosimetry showed that at one day, the 25 percent blend actually had the densest pore structure of all mixtures, its fine carbonate particles physically plugging capillary spaces and seeding gel precipitation. But by seven days the control had overtaken it, its ongoing slag reaction churning out enough binding gel to fill pores faster than any filler could. In the high-replacement blends, pore refinement with age was visible but limited, because the reactive slag reservoir had simply been drawn down too far. Densification, in other words, is ultimately paid for in reactive calcium, silicon and aluminum, and the carbonated waste can only subsidize that budget, not replace it.

The study is candid about its limits. The experiments were run on pastes, so aggregates, interfacial transition zones, workability and long-term durability in real concrete remain untested, and the indicative carbon accounting, which weighs roughly 0.052 kilograms of CO2-equivalent per kilogram of slag against 130 kilograms of CO2 fixed per ton of carbonated waste, deliberately excludes the energy costs of pressurized carbonation, drying, gas compression and activator production. A full life-cycle assessment is still needed before the approach can claim genuine climate benefits. Even so, the core finding stands: at moderate replacement levels, a CO2-sequestering waste powder can shoulder a quarter of the binder workload in a slag geopolymer while preserving most of its strength. In an industry staring down carbon border taxes and trillion-dollar decarbonization bills, the idea that yesterday’s concrete sludge, inflated with captured carbon, could help build tomorrow’s foundations is exactly the kind of circular-economy alchemy the built environment needs.

Subject of Research: Use of carbonated concrete slurry waste as a partial precursor replacement in GGBS-based geopolymer pastes

Article Title: Effect of carbonated concrete slurry waste incorporation on the geopolymerization, mechanical performance, and microstructural evolution of GGBS-based geopolymer pastes

Article References: Sim, S. (2026). Effect of carbonated concrete slurry waste incorporation on the geopolymerization, mechanical performance, and microstructural evolution of GGBS-based geopolymer pastes. Case Studies in Construction Materials, 25, Article e06608. https://doi.org/10.1016/j.cscm.2026.e06608

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06608

Keywords: geopolymer, GGBS, concrete slurry waste, carbonation, CO2 sequestration, C-(N)-A-S-H gel, compressive strength, calcite, FT-IR spectroscopy, microstructure, sustainable construction, alkali-activated materials

The material belongs to a family of substances known as geopolymers — amorphous, metastable aluminosilicates first developed by Joseph Davidovits in 1970. They are synthesized by reacting an aluminosilicate precursor, such as calcined clay, fly ash, or natural pozzolans, with an alkaline activator like sodium hydroxide at temperatures below 100 degrees Celsius. At the molecular level, the result is an anionic framework of corner-sharing SiO4 and AlO4 tetrahedra, into which charge-balancing cations such as sodium or potassium are incorporated from solution. This architecture gives geopolymers a set of properties that make them unusually attractive for water treatment: low-cost and abundant precursors, tunable porosity, chemical stability, and a synthesis route that is gentle on the environment. Their adjustable surface chemistry and robust structural framework also support adsorption efficiency and recyclability, addressing two of the biggest weaknesses of conventional adsorbents.

What distinguishes the new work is its dual pore-generation strategy and its systematic exploration of precursor composition. The team calcined kaolin from Zettlitz in the Czech Republic at 700 degrees Celsius for three hours to produce metakaolin, then blended it with silica fume — an ultrafine byproduct of ferrosilicon and silicon metal production, containing more than 96 percent amorphous silica and a surface area of roughly 20,000 square meters per kilogram. Silica fume replaced metakaolin at proportions ranging from 0 to 25 weight percent, serving as a reactive silica source within the alkaline activator system. To open up the internal architecture, the researchers added hydrogen peroxide at 5 weight percent as a foaming agent, which decomposes to generate gas-induced pores, and corn oil at 1 weight percent as a templating phase that promotes interconnected voids. The paste was cured at 60 degrees Celsius for 12 hours, followed by hydrothermal curing for another 24 hours, before being crushed, sieved to particles below 100 micrometers, washed with hot water, and dried.

The screening experiments revealed a striking optimum. When six adsorbent formulations were tested against a 10 milligram per liter methylene blue solution at natural pH with a dosage of 1 gram per liter, both adsorption capacity and removal efficiency climbed as silica fume content rose to 10 percent, where the S(10) formulation achieved roughly 90 percent removal. Beyond that threshold, performance declined. The explanation lies in the structural evolution of the geopolymer: at 10 weight percent, the additional reactive silica facilitates more complete polycondensation, producing a robust and well-distributed sodium aluminosilicate hydrate gel with a balanced silicon-to-aluminum ratio that maximizes negatively charged surface sites for cationic attraction. Above that level, particle agglomeration reduces available surface area, partially blocks mesoporous channels, and increases paste viscosity — which hinders uniform distribution of the hydrogen peroxide foam and yields a less interconnected pore structure riddled with physical defects.

With the optimal composition identified, the researchers mapped how operating conditions shape performance. Increasing the adsorbent dosage from 0.5 to 2.5 grams per liter raised removal efficiency from 60 to 93 percent, though the amount adsorbed per gram of material fell from 11.52 to 3.84 milligrams as sites began to overlap and aggregate. pH proved decisive: removal efficiency rose from 58.5 percent at pH 1 to 93 percent at pH 7, then slipped slightly to 90.5 percent at pH 9. The chemistry is intuitive — under acidic conditions, the geopolymer surface is surrounded by hydrogen ions and acquires a positive charge, electrostatically repelling the cationic dye, while neutral conditions maximize the attraction between dye cations and the negatively charged surface. Notably, the optimum coincides with the material’s point of zero charge, and because real textile effluents often require expensive pH adjustment before treatment, the ability to perform best at near-neutral conditions could meaningfully cut operational costs. Contact time experiments showed 73.05 percent removal within the first 30 minutes, reaching equilibrium at 60 minutes with 93.6 percent removal.

Kinetic modeling pointed to a chemical rather than purely physical binding process. The pseudo-second-order model fit the data with a correlation coefficient of 0.99, far outperforming the pseudo-first-order model at 0.84 and the Elovich model at 0.7 — a signature of chemisorption, in which electron sharing or exchange between adsorbent and adsorbate governs the rate. The intraparticle diffusion model fit poorly, and its non-zero intercept confirmed that pore diffusion is not the sole rate-limiting step; boundary layer resistance and film diffusion also contribute to mass transfer. On the equilibrium side, the Langmuir isotherm described the data best with a correlation coefficient of 0.98, ahead of the Freundlich model at 0.94 and the Temkin model at 0.92. Together, the kinetic and isotherm analyses indicate monolayer chemisorption on energetically equivalent sites, with a maximum adsorption capacity of 12.30 milligrams per gram and a separation factor of 0.064 confirming favorable adsorption.

Spectroscopic and microscopic analyses supplied direct evidence of how the dye molecules attach. Fourier transform infrared spectroscopy showed a reduction and shift of the primary silicon-oxygen-aluminum vibration band between 850 and 1200 wavenumbers after dye uptake, alongside the appearance of methylene blue-specific signals near 1243, 1100, and 1400 wavenumbers, attributed to C–N and N–N stretching and aromatic ring deformations. Changes in the broad hydroxyl stretching region near 3400 wavenumbers suggested hydrogen bonding between surface hydroxyl groups and the dye. X-ray diffraction revealed the characteristic broad amorphous hump of the N-A-S-H gel, which broadened slightly after adsorption but returned to its original profile after regeneration, confirming structural stability. Nitrogen sorption measurements classified the material as mesoporous, with a Type IV isotherm and H3-type hysteresis loop indicating slit-like or ink-bottle-shaped pores, a specific surface area of 12.515 square meters per gram, and an average pore diameter of 31.7 nanometers — dimensions that facilitate rapid transport of dye molecules to internal active sites. Scanning electron microscopy showed pores partially coated and filled after adsorption, with elemental mapping revealing increased carbon and nitrogen content that vanished after regeneration.

The adsorption mechanism that emerges is a layered one. Negatively charged siloxo and alumoxo sites on the geopolymer surface attract the cationic dye electrostatically, while charge-balancing sodium ions within the pores undergo direct ion exchange with methylene blue cations. The dye molecule adopts a more planar configuration, lying flat on the surface, which facilitates π–π interactions between its aromatic rings and silanol groups, and the presence of aluminum and sodium ions combined with the dye’s conjugated structure may induce additional n–π interactions. Hydrogen bonding with surface functional groups further enhances uptake. Initial capture is assisted by van der Waals forces, dipole–dipole interactions, and physical pore filling within the mesoporous network, but the rate is ultimately governed by the abundance of accessible surface sites rather than diffusion alone.

Perhaps most importantly for real-world deployment, the adsorbent proved reusable. Over five adsorption–desorption cycles, removal efficiency declined from 93.6 percent to approximately 73 percent when regenerated with hydrochloric acid and to about 80 percent when regenerated with ethanol. Ethanol proved the superior regenerant: its lower dielectric constant weakens the electrostatic grip between dye cations and the negatively charged surface, while it competes for silanol and aluminol binding sites through hydrogen bonding and solvates the dye’s aromatic rings. The residual capacity loss stems from irreversible chemisorption at high-energy sites and partial pore masking in narrow mesopores, where dye molecules bound through strong chemical interactions resist displacement. Even so, retaining 80 percent efficiency after five cycles is a commendable result that addresses the common criticism that adsorption merely transfers pollutants from water to a solid that must then be discarded.

The researchers are candid about the material’s limits. Its maximum capacity of 12.30 milligrams per gram trails some highly porous commercial adsorbents and engineered materials, a consequence of the relatively modest surface area and the absence of additional surface functionalization. Yet the comparison that matters may be economic rather than absolute: the removal efficiency of 93.6 percent rivals that of far more elaborate systems, and the synthesis route relies on low-cost, widely available industrial wastes — silica fume from ferroalloy furnaces and calcined clay — while operating at mild temperatures without energy-intensive processing. The team suggests that surface tailoring, chemical modification, or the incorporation of carbon-based materials, metal oxides, or nanoscale additives could push performance further, and that testing under real wastewater conditions, long-term reuse, and continuous-flow systems will be needed to establish broader applicability. For now, the study demonstrates that two industrial waste streams, a splash of hydrogen peroxide, and a spoonful of cooking oil can be transformed into a working water-cleaning material — a small but compelling example of circular chemistry aimed at one of the world’s most persistent pollution problems.

Subject of Research: Porous metakaolin–silica fume geopolymer adsorbents for removing methylene blue dye from contaminated water

Article Title: Eco-friendly production of porous metakaolin–silica fume geopolymer for adsorptive removal of methylene blue from water

Article References: Oshani, F., Mahinroosta, M., & Ghasemi, E. (2026). Eco-friendly production of porous metakaolin–silica fume geopolymer for adsorptive removal of methylene blue from water. Results in Engineering, 32, Article 113419. https://doi.org/10.1016/j.rineng.2026.113419

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113419

Keywords: geopolymer, methylene blue, adsorption, silica fume, metakaolin, wastewater treatment, dye removal, porous materials, chemisorption, water purification, industrial byproducts, sustainability

The team’s starting material was dredged sludge from Nanjing, in China’s Jiangsu Province, a silty clay with a water content of 33 percent, a liquid limit of 35.3 percent and a plasticity index of 16.6. Classified as silty clay because of its 73 percent silt fraction, the soil in its natural state has a loose microstructure and poor mechanical strength, making it unsuitable for load-bearing embankment fill without treatment. Compaction testing showed the soil reaches its maximum dry density at a water content of 14 percent, a figure the researchers used to design their mixtures.

Rather than relying on Portland cement, whose production accounts for a substantial share of global carbon dioxide emissions, the researchers turned to two abundant industrial by-products. Fly ash, captured from coal combustion flue gases, is rich in silica and alumina, while granulated blast furnace slag from ironmaking contributes abundant calcium. Both materials pose disposal problems of their own; uncontrolled fly ash can generate airborne dust and contaminate water. Under alkaline activation with sodium hydroxide and sodium silicate, however, these wastes dissolve and recombine into powerful cementitious gels, turning a liability into a resource.

To find the best formulation, the team ran an orthogonal test program examining four variables: the fly ash to slag ratio, the sodium hydroxide to sodium silicate ratio, the total alkali content and the water to solid ratio. Variance analysis revealed that the fly ash to slag ratio exerted the strongest influence on compressive strength, followed by alkali content, water to solid ratio and finally the activator balance. The optimal recipe emerged as an equal 5:5 blend of fly ash and slag, a sodium hydroxide to sodium silicate ratio of 1:7, an alkali content of 10 percent by mass of the binder, and a water to solid ratio of 0.35. The researchers attributed the strength gains to abundant calcium aluminate crystals that fill pores when the activator chemistry is properly balanced, while too much or too little water either leaves binder unreacted or dilutes the activator concentration.

With the optimal binder in hand, the team blended it into the dredged soil at doses ranging from 2 to 10 percent by mass and cured the compacted cylindrical specimens for 28 days under standard laboratory conditions of 20 degrees Celsius and 95 percent humidity, deliberately avoiding the high-temperature curing that pure fly ash geopolymers typically require. The results showed a clear threshold effect. Below about 4 percent binder content, the newly formed gel mainly repairs the cohesive soil structure disturbed by mixing, so properties improve only modestly. Above that threshold, enough gel is produced to bond soil particles into a genuinely new, stable skeleton, and performance climbs steeply. Compared with untreated soil, the 10 percent mixture delivered a 110 percent gain in compressive strength, a 106 percent increase in toughness index, a 243 percent boost in tensile strength and an 85 percent improvement in the water stability coefficient.

That last metric matters enormously for embankments, which must survive rainfall and saturation. The researchers saturated specimens after 21 days of curing and compared their strength with samples kept dry. Stress-strain curves showed the stabilized soil fails in a softening, plastic manner rather than shattering brittlely, absorbing energy before gradually losing load capacity. The toughness index, calculated as the area under the stress-strain curve up to peak strain, quantified this resistance to brittle fracture and rose steadily with binder dose.

Head-to-head against a conventional 4 percent cement-stabilized control, the picture was nuanced. At equal 4 percent dosage, the alkali-activated material lagged behind cement, with compressive strength, tensile strength and water stability reduced by 44, 53 and 21 percent respectively, because cement’s higher calcium content generates more calcium silicate hydrate gel. But at 10 percent dosage, the waste-based binder overtook cement on every measure, edging ahead by 4 percent in compression, 13 percent in tension and 14 percent in water stability. The trade-off is more binder, but one made entirely from wastes that would otherwise be landfilled.

The environmental accounting is where the new binder truly shines. Using life cycle assessment aligned with ISO 14040, the team quantified global warming potential, acidification, eutrophication, photochemical ozone creation and resource consumption for stabilizing one tonne of soil. The 4 percent alkali-activated mixture cut global warming potential by 99 percent relative to cement treatment, from 71.6 kilograms to 0.363 kilograms of carbon dioxide equivalent, while acidification, eutrophication and photochemical oxidation potentials fell by 100, 99 and 91 percent and resource consumption dropped 98 percent. Even the 10 percent mixture, using twice the binder mass, reduced global warming potential by 99 percent and resource consumption by 95 percent compared with the cement control.

To understand why the material performs so well, the researchers deployed an arsenal of microscopic techniques: X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy with energy dispersive spectroscopy, and nuclear magnetic resonance. Electron images revealed that untreated soil consists of blocky, flaky and flocculated particle aggregates riddled with voids, while the 10 percent mixture forms a dense fabric of flocculent gel bonding particles into lumpy aggregates. Image analysis showed porosity falling by 25 percent at 4 percent binder and 70 percent at 10 percent. Nuclear magnetic resonance confirmed that large pores declined by 75 percent and small pores by 28 percent at the highest dose, indicating the gel primarily bridges particles and eliminates large voids while also filling finer ones. Notably, no spherical fly ash particles survived, evidence that the ash dissolved and reacted almost completely.

The spectroscopic data converged on a clear chemical mechanism. Elemental analysis detected oxygen, sodium, aluminum, silicon and calcium, with sodium, calcium and aluminum to silicon ratios rising sharply with binder dose. Under the alkaline conditions created by sodium hydroxide and sodium silicate, Ca-O, Na-O, Al-O and Si-O bonds break, releasing calcium ions, sodium ions, aluminate and silicate species that then geopolymerize. Slag-derived calcium forms calcium silicate hydrate and calcium aluminosilicate hydrate gels, while fly ash contributes to sodium aluminosilicate hydrate, the signature N-A-S-H gel of alkali-activated systems. X-ray diffraction identified these new gel phases alongside the soil’s native quartz, illite and kaolinite; infrared spectra showed strengthened Si-O and Al-O absorption bands; and thermal analysis recorded additional mass losses from gel decomposition and bound water, cross-validating the mechanism. The gels weld soil particles into a stable skeleton and fill pores, explaining the dramatic mechanical and durability gains. The authors note that future work must test the material against sulfate attack, high temperatures and freeze-thaw cycling, but the study establishes that two of the world’s most troublesome industrial wastes can jointly convert dredged mud into a durable, genuinely low-carbon construction material.

Subject of Research: Alkali-activated fly ash and blast furnace slag stabilization of dredged waste soil for sustainable embankment construction

Article Title: Applicability and chemical mechanism of alkali-activated fly ash and blast furnace slag stabilized soil for sustainable embankment

Article References: Zhang, C., Wang, W., Zhu, Z., Li, N., Jang, P., & Ma, B. (2026). Applicability and chemical mechanism of alkali-activated fly ash and blast furnace slag stabilized soil for sustainable embankment. Case Studies in Construction Materials, 25, Article e06619. https://doi.org/10.1016/j.cscm.2026.e06619

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06619

Keywords: alkali-activated materials, fly ash, blast furnace slag, soil stabilization, embankment, geopolymer, dredged sludge, low-carbon construction, life cycle assessment, N-A-S-H gel, C-A-S-H gel, waste recycling

The research team, led by Lan-Ping Qian and Ti-Lin Fang with colleagues including Xiuli Du, focused on geopolymer, a low-carbon cementitious material formed by activating aluminosilicate-rich industrial residues with an alkaline solution. Geopolymers already attract attention because they can slash the carbon emissions associated with conventional cement, and their amorphous three-dimensional aluminosilicate network provides a dielectric environment in which electromagnetic energy can be dissipated. But the field faces a raw-material bottleneck. Most geopolymer shielding studies rely on fly ash from coal-fired power plants and ground granulated blast-furnace slag, and as China’s energy structure shifts away from coal, high-quality fly ash is becoming scarcer. The researchers turned instead to two of the world’s most problematic waste streams: red mud and ore tailings.

The scale of these waste streams is enormous. Red mud, the highly alkaline residue left after alumina is extracted from bauxite, accumulates globally at a rate of roughly 60 to 120 million tons per year, with stockpiles exceeding 4.1 billion tons. Ore tailings, the ground rock left after metals such as copper are extracted, are generated at approximately 1.4 billion tons annually. Both materials are rich in iron-bearing and other metal-containing phases that can promote dielectric loss and interfacial polarization, giving them a latent electromagnetic function, and both contain active aluminosilicate components suitable for geopolymer synthesis. In the new work, red mud and two types of ore tailings, one from a Qinghai mining operation and one from Xinjiang, replaced 20, 40, and 60 percent of the fly ash in a fly ash and slag geopolymer matrix, with carbon fibers held constant at 0.5 percent by mass to provide a baseline conductive framework.

The mechanical results revealed sharply divergent roles for the two wastes. Red mud consistently undermined strength: at 60 percent fly ash replacement, the 28-day compressive strength dropped 49 percent relative to the control, from a robust baseline down to just 23.3 megapascals. X-ray diffraction explained why. Red mud is dominated by crystalline hematite and cancrinite, and these inert crystalline phases appear to hinder the dissolution and polycondensation reactions of the active aluminosilicates that build the binding gel. The ore tailings behaved in exactly the opposite fashion. Both tailings types raised compressive strength above the control at every replacement level, with the 60 percent replacement of the first tailings reaching 68.0 megapascals, the highest value among the fiber-free mixes. The tailings had been ball-milled before use, and their fine particles acted as micro-aggregates, filling pores and densifying the matrix. Nitrogen adsorption analysis confirmed that tailings substitution increased the proportion of harmless pores below 20 nanometers and reduced harmful pores above 50 nanometers, a pore refinement that translated directly into mechanical gains.

Electrical measurements underscored the complementary role of each component. The plain geopolymer control had a 28-day alternating-current resistivity of 426 ohm-centimeters, but substituting red mud or tailings for fly ash lowered that value moderately, because the alkaline red mud supplies abundant hydroxyl ions and iron oxide while the milled tailings release soluble calcium, sodium, and hydroxide ions and refine the pore network into connected capillary pathways. Adding 0.5 percent carbon fibers then produced a dramatic step change, cutting resistivity by roughly an order of magnitude across all systems. The lowest values reached 12.7 ohm-centimeters for the first tailings and 10.6 ohm-centimeters for the second at 60 percent replacement, 40.9 and 50.7 percent below the fiber-only control, evidence that a more effective conductive network had formed when the waste-modified matrix and the fibers worked together.

Electromagnetic shielding tests in the X-band, the 8.2 to 12.4 gigahertz range used by aviation, military, and weather radar, showed how these electrical changes translated into functional performance. Without carbon fibers, the plain geopolymer achieved a total shielding effectiveness of about 15 decibels, and replacing fly ash with the wastes raised the peak value by as much as 6 decibels, up to 22.7 decibels for the first tailings at 12.4 gigahertz. The mechanism was subtle and counterintuitive: the moderate conductivity increase improved impedance matching, allowing more electromagnetic waves to penetrate the material’s surface rather than bounce off it, so the waves could be absorbed and dissipated inside. Transmittance in the first-tailings matrix fell below 2.3 percent, and absorption rather than reflection became the dominant shielding pathway.

With carbon fibers present, the physics shifted again. The fibers established continuous conductive pathways, triggering a strong skin effect in which incident waves concentrate near the highly conductive surface and are largely reflected, dropping transmittance below 0.1 percent, while penetrating waves were dissipated through conduction loss, boosting the absorption component by roughly 14 decibels. Against this fixed fiber framework, the waste modifiers fine-tuned the balance between reflection and absorption. Red mud acted as an absorption-favorable modifier: the 60 percent red mud composite with fibers maintained a total shielding effectiveness above 25 decibels, peaked at 30.5 decibels at 8.2 gigahertz, and showed roughly 10 percent higher absorptance than the fiber-only control, though at the cost of the lowest compressive strength, 26.6 megapascals, among the fiber-reinforced mixes. The two tailings delivered the best all-around results. The first tailings at 60 percent replacement reached a measured peak shielding effectiveness of 32.2 decibels at 11.92 gigahertz with transmittance below 0.09 percent, while the second tailings achieved the study’s maximum of 33.5 decibels at 8.2 gigahertz and held transmittance below 0.06 percent.

Those numbers place the material in impressive company. At only 5 millimeters thick and containing just 0.5 percent carbon fiber, the composite achieves a thickness-normalized shielding effectiveness of 6.7 decibels per millimeter, higher than geopolymer systems loaded with 3.75 percent cork, 60 percent slag, or silica-coated carbon nanotubes, and it approaches the performance of composites that require five to ten times more carbon fiber. Mechanistic analysis using Cole-Cole plots revealed Debye-type relaxation behavior arising from interfacial polarization at the many heterogeneous boundaries between unreacted particles, gel matrix, and carbon fibers, while the frequency dependence of the imaginary permittivity confirmed that conduction loss, driven by the fiber network, was a major dissipation channel. Magnetic loss, by contrast, proved negligible across all formulations, since permeability values remained close to unity.

Microstructural imaging tied the story together. Scanning electron microscopy showed carbon fibers embedded snugly in the matrix without large interfacial gaps, bridging microcracks and suppressing their propagation, which explains the modest strength enhancement the fibers provided. Backscattered electron mapping revealed interwoven calcium-rich gels around slag particles and aluminum-silicon-rich gels around fly ash, with iron concentrated in discrete spots inherited from the waste precursors, confirming that the wastes were not inert passengers but active participants reshaping the gel chemistry and pore architecture. The authors are appropriately cautious, noting that because only one independently prepared specimen was evaluated for each mixture in the electromagnetic tests, differences of one to two decibels should be read as comparative trends rather than statistically validated improvements, and that small-specimen waveguide measurements are not fully equivalent to the shielding of full-scale wall panels.

Even with those caveats, the study’s implications are considerable. It demonstrates that red mud and ore tailings are not merely substitutes for dwindling fly ash but genuine matrix modifiers that can be chosen according to need: tailings when strength and balanced shielding are priorities, red mud when absorption-dominant shielding matters more than mechanical performance. As electromagnetic pollution intensifies and the construction industry confronts its carbon problem, the idea that the walls of future buildings could simultaneously lock away billions of tons of hazardous waste, bear structural loads, and quietly absorb radar and wireless signals transforms two environmental liabilities into a single functional material. The next steps, the researchers suggest, involve exploring different fiber contents, specimen thicknesses, frequency bands, and long-term durability, moving this waste-to-shield concept from the waveguide bench toward the built environment.

Subject of Research: Electromagnetic shielding and compressive strength of carbon-fiber-reinforced geopolymer composites modified with red mud and ore tailings

Article Title: Tuning electromagnetic shielding and compressive strength of carbon-fiber-reinforced geopolymer using red mud and ore tailings

Article References: Qian, L.-P., Fang, T.-L., Xu, L.-Y., Shi, D.-D., Peng, K.-D., Li, Y., & Du, X. (2026). Tuning electromagnetic shielding and compressive strength of carbon-fiber-reinforced geopolymer using red mud and ore tailings. Case Studies in Construction Materials, 25, Article e06599. https://doi.org/10.1016/j.cscm.2026.e06599

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06599

Keywords: geopolymer, electromagnetic shielding, red mud, ore tailings, carbon fiber, fly ash, compressive strength, dielectric loss, impedance matching, industrial solid waste, X-band, sustainable construction

The material at the center of the study, rubberized alkali-activated concrete, or RuAAC, combines two waste streams in a single matrix. The binder forms through a chemical reaction between an alkaline activator solution and aluminosilicate precursors, avoiding the high-temperature clinker process entirely. In this work, the binder comprised ground granulated blast furnace slag and Class F fly ash in a one-to-three ratio, activated by a blend of sodium silicate and 12 molar sodium hydroxide. The team tested three rubber gradations, a fine-graded fraction spanning 0 to 0.8 millimeters, a medium-graded fraction of 1 to 3 millimeters, and a wide-range blend covering 0 to 3 millimeters, each incorporated at 5, 10, and 20 percent replacement of fine aggregate by volume. Crucially, the rubber was used exactly as received from the tire recycling plant, with no chemical pre-treatment, a deliberate choice to preserve the environmental and economic case for the material, since soaking and rinsing procedures consume reagents, water, and generate effluent of their own.

The results on strength tell a story of trade-offs. The control mix, with no rubber, reached an impressive 72.3 megapascals at 28 days, reflecting the rapid reaction kinetics of the slag-rich binder. Adding rubber reduced compressive strength across the board, with losses ranging from 21 to 35 percent at 5 percent replacement, 30 to 46 percent at 10 percent, and 36 to 56 percent at 20 percent. But the gradation made an enormous difference. The fine-graded mixes retained the highest strengths at every dosage, reaching 57.1 megapascals at just 5 percent rubber, while the wide-range mixes performed worst, falling to 31.7 megapascals at 20 percent. The reason lies at the microscopic interface between the hydrophobic rubber particles and the hydrophilic alkali-activated gel. Residual zinc stearate from the tire vulcanization process repels the polar activator, entraining air voids at the interface and creating weak interfacial transition zones that act as flaws under load. Larger particles create larger, more critical defects, while sub-millimeter particles distribute the damage into smaller, less consequential discontinuities.

One of the most intriguing findings concerned early-age behavior. At just one day, the rubberized mixes were 40 to 72 percent weaker than the control, but this deficit narrowed substantially by 28 days. The rubber particles, it turns out, delay rather than suppress the alkali-activation reaction. The fine- and medium-graded mixes more than doubled their strength between one and seven days, recovering much of the early loss as the matrix densified around the inclusions. Statistical analysis using two-way analysis of variance confirmed this interpretation: the interaction between rubber content and gradation was significant at one day but not at later ages, meaning the gradation-specific early damage faded as the reaction progressed. By contrast, the medium-graded mix at 20 percent replacement gained almost no strength after seven days, suggesting that failure in that mix was governed by the weak interfaces around its uniform 1 to 3 millimeter particles rather than by the still-reacting matrix.

Where rubber genuinely shines is in deformation capacity. The control concrete failed in classic brittle fashion, with a sharp post-peak drop in the stress-strain curve. The rubberized mixes, by contrast, softened gradually and kept carrying load at strains approaching 0.8 percent or more. The ductility index, a measure of how much a material can deform before failure, rose by 44 percent in the fine-graded mix at 20 percent replacement compared with the control. The elastic rubber particles store strain energy and delay the coalescence of microcracks into macrocracks, transforming a sudden fracture into a controlled, gradual failure. This exchange of strength for toughness is precisely the property profile needed for applications such as crash barriers, pavement slabs, and industrial floors, where energy absorption and crack resistance matter as much as raw load capacity.

The study also broke new ground by measuring direct shear strength, load-slip response, and shear toughness of RuAAC for the first time at the material level, a gap with real safety implications. Shear failures in structural elements such as flat slabs, corbels, and deep beams occur with little warning, and design codes estimate shear capacity as a function of the square root of compressive strength using coefficients calibrated to Portland cement concrete. The team found that shear strength declined by up to 45 percent with rubber incorporation, less severely than flexural strength, which fell by as much as 67 percent, because confining stresses developed during shear testing provided mechanical interlock that partially compensated for the weak rubber-matrix bonding. Notably, at 5 percent fine-graded rubber, the shear toughness index was 25 percent higher than the control, suggesting that modest rubber dosages can genuinely improve energy dissipation along crack planes.

The durability results delivered some of the study’s most surprising wins. Water absorption in the fine-graded mix at 20 percent replacement was 9 percent lower than the control, and its capillary absorption depth at six hours was 39 percent lower, because the densely dispersed hydrophobic particles interrupt continuous capillary pathways and force water to take longer, more tortuous routes through the matrix. Bulk electrical resistivity, a proxy for resistance to chloride ingress and rebar corrosion, was 12 percent higher than the control in the same mix. Abrasion resistance told a dramatic gradation-dependent story: the fine-graded mix at 20 percent lost 29 percent less mass than the control after 500 tumbling cycles, while every medium-graded mix disintegrated completely, with the 20 percent medium-graded specimen failing by just 200 cycles. The uniform 1 to 3 millimeter particles, poorly bonded to the matrix, acted as discrete weak points that accelerated crack propagation under surface wear.

The authors distilled their findings into two practical application regimes, both built on fine-graded rubber. A mix with 5 percent fine crumb rubber retained 57.1 megapascals of compressive strength, a 25 percent higher shear toughness index, and better abrasion resistance than the control, making it suitable for pavement slabs, industrial floors, curbs, and precast panels. A mix with 20 percent fine rubber offers lower strength, 46.1 megapascals, but a 44 percent higher ductility index, reduced density, and improved workability, pointing toward crash barriers and non-structural cladding. The researchers caution that the reduced elastic modulus, between 14.2 and 19.2 gigapascals compared with 24.3 for the control, means deflection rather than strength will likely govern member sizing, and that shear-governed elements require member-scale testing before RuAAC can be deployed in them.

What makes this work resonate beyond the laboratory is its reframing of a familiar sustainability equation. Simply dumping waste into concrete is not enough; the form of the waste determines whether the resulting material is an engineering asset or a liability. By demonstrating that sub-millimeter tire rubber can simultaneously cut cement demand, divert landfill waste, improve ductility, and even enhance durability, the study offers a credible pathway for rubberized cement-free concrete to move from non-structural novelty toward genuine structural relevance. The authors call for microstructural examination of the rubber-matrix interface, extended durability testing covering chloride penetration, carbonation, freeze-thaw and creep, full-scale element testing, and a life cycle assessment quantifying embodied carbon per unit of strength. Until then, the message is clear: if you want tires to strengthen the future of concrete, grind them fine.

Subject of Research: Effect of recycled crumb rubber particle size and replacement level on the mechanical and durability properties of cement-free alkali-activated concrete

Article Title: Effect of recycled rubber particle size and replacement level on the properties of rubberized alkali-activated concrete

Article References: Elbaz, Y., Mwafy, A., El-Maaddawy, T., & El-Hassan, H. (2026). Effect of recycled rubber particle size and replacement level on the properties of rubberized alkali-activated concrete. Results in Engineering, 32, Article 113326. https://doi.org/10.1016/j.rineng.2026.113326

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113326

Keywords: alkali-activated concrete, crumb rubber, waste tires, geopolymer, compressive strength, shear strength, ductility, durability, water absorption, abrasion resistance, sustainable construction, fly ash slag binder

The logic behind the design draws on two well-established strands of environmental chemistry. Geopolymers, first described by Joseph Davidovits in 1991, are aluminosilicate materials formed by alkali activation of precursors such as metakaolin, and they have repeatedly shown promise as adsorbents for dissolved metals. Biosorption, meanwhile, exploits the dense array of functional groups on microbial cell walls, which can bind metal ions through complexation and exchange. The challenge has always been practicality: free-floating microbial biomass is difficult to handle, separate and reuse in real treatment systems. Immobilization solves that problem by anchoring the cells onto a solid carrier, and the new study demonstrates that a geopolymer can serve as that carrier through simple passive contact rather than elaborate chemical grafting.

To understand what makes JEONS5 tick, the team subjected the material to a battery of analytical techniques. Zeta potential measurements mapped the surface charge of the composite across the relevant pH range, while Fourier-transform infrared spectroscopy identified the chemical groups available for binding, including hydroxyl, amine, carbonyl, C–N, Si–O and Al–O functionalities. Scanning electron microscopy paired with energy-dispersive X-ray spectroscopy revealed the morphology of the fungal cells integrated into the geopolymer matrix and confirmed the presence of lead after uptake. X-ray diffraction, X-ray fluorescence and X-ray photoelectron spectroscopy rounded out the picture, allowing the researchers to track how the surface chemistry of the hybrid changed as it captured Pb2+ ions from solution.

Batch experiments established the operating conditions for maximum performance. At a pH of 5.0 and a modest sorbent dosage of just 0.04 grams, the material removed more than 95 percent of lead from a solution containing 100 milligrams of Pb2+ per liter. That dosage figure is notable in itself, because it means only a small quantity of the composite is needed to treat a given volume of contaminated water, which directly affects the cost and footprint of any future treatment process. The team also found that uptake was essentially independent of temperature, suggesting the binding interaction is not strongly thermally activated and that performance should hold steady across a range of ambient conditions.

Speed is where the material truly stands out. Equilibrium was reached in roughly 30 minutes, and more than 75 percent of the total lead uptake occurred within the first five minutes of contact. For water treatment engineers, that kind of kinetics matters enormously: rapid uptake translates into shorter contact times, smaller reactor volumes and higher throughput in continuous systems. The kinetic data fit a pseudo-second-order model well, a pattern typically interpreted as indicating that the rate-limiting step involves chemical interactions between the metal ions and the binding sites rather than simple diffusion to the surface.

Equilibrium data, meanwhile, were best described by the Langmuir isotherm model, which assumes a finite number of uniform binding sites on the sorbent surface. From that fit the team calculated a maximum uptake capacity of 1.05 × 10⁻³ moles per gram, equivalent to 217.56 milligrams of lead per gram of material. That figure places JEONS5 among the more capable biosorbents reported for lead, and the authors attribute the capacity to the joint activity of the geopolymer framework and the fungal cells, each contributing distinct binding chemistry to the composite.

Because real treatment plants rarely operate in batch mode, the researchers also tested the material in a fixed-bed column configuration, the geometry most commonly used in industrial adsorption. The column showed a breakthrough point at 20 minutes and an exhaustion point at 350 minutes, defining the window during which the bed delivers treated water below the target concentration. The shape of the breakthrough curve was fairly well captured by Chu’s simplistic model, a modern analytical tool for fixed-bed adsorption data, which gives engineers a way to predict column performance without resorting to computationally intensive simulations.

Perhaps the most consequential result concerns reuse. Regeneration tests showed that JEONS5 retained sorption and desorption efficiencies above 90 percent through its first ten loading and unloading cycles, and even at the end of the twentieth cycle the material still delivered 50 percent of its original sorption efficiency. Reusability is the economic linchpin of any adsorbent technology, since a material that must be replaced after a handful of cycles quickly becomes more expensive than conventional alternatives. Twenty usable cycles, with the possibility of recovering the captured lead during desorption, points toward a genuinely practical process rather than a laboratory curiosity.

The mechanistic picture that emerges from the spectroscopic evidence is one of multiple pathways operating in parallel. The authors conclude that lead capture proceeds through surface complexation, in which Pb2+ coordinates directly with functional groups on the composite; ion exchange, in which lead displaces other cations from the geopolymer framework; and electrostatic interactions, in which the charged surface attracts the metal ions. This redundancy is a strength, because a sorbent that relies on a single mechanism can be vulnerable to changes in water chemistry, whereas a multi-pathway material should perform more robustly across diverse contaminated waters.

The study, funded by the Scientific and Technological Research Council of Türkiye under project number 123Y131, arrives amid growing pressure to find low-cost, low-waste methods for heavy metal remediation. Lead exposure remains a serious public health concern worldwide, with no known safe blood level, and contaminated water is a major exposure route. A sorbent that combines abundant raw materials, a simple passive immobilization step, rapid kinetics, a high capacity and demonstrated reusability addresses several of the barriers that have kept biosorption technologies out of mainstream practice. The researchers argue that JEONS5 has enormous potential for treating Pb2+-contaminated aquatic systems, and the next test for the material will be demonstrating that performance on real industrial effluents, where competing ions and organic matter complicate the chemistry far beyond the clean laboratory solutions used in this study.

Subject of Research: A geopolymer-immobilized fungal biosorbent for removing toxic lead ions from contaminated water

Article Title: Geopolymer fungal cell integration achieved through passive immobilization: a new sustainable candidate to effectively remove toxic lead contamination

Article References: Akar, T., Sayin, F., Tunali Akar, S., Kara, I., Celik, S., Çınar, H., Özen, G., & Kara, F. (2026). Geopolymer fungal cell integration achieved through passive immobilization: a new sustainable candidate to effectively remove toxic lead contamination. Environmental Geochemistry and Health, 48(16), Article 628. https://doi.org/10.1007/s10653-026-03515-y

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03515-y

Keywords: geopolymer, Neurospora, biosorption, lead removal, heavy metal remediation, water treatment, immobilized cells, hybrid sorbent, adsorption kinetics, Langmuir isotherm, fixed-bed column, sustainable materials

The choice of ingredients is deliberate and each component plays a distinct structural role. Diatomite, a silica-rich sedimentary rock formed from the fossilized frustules of microscopic algae and sourced from Lampang in northern Thailand, supplies an intrinsically porous mineral framework that facilitates mass transfer of dye molecules into the pellet interior. Metakaolin, produced by calcining kaolin clay from Ranong, serves as the reactive aluminosilicate precursor that forms the chemically stable geopolymer network when activated with a mixture of sodium silicate solution and 10 M sodium hydroxide. Water hyacinth residue collected in Chiang Mai brings oxygen-rich functional groups and a fibrous morphology that modify the pore architecture and surface reactivity of the final composite. The researchers cast pastes containing 20 weight percent calcined diatomite, 15 weight percent metakaolin, and the alkaline activator, adding water hyacinth at 0, 1, 2, and 3 weight percent to produce a series labeled DG-WH0 through DG-WH3, which were then cured at room temperature for up to 28 days.

Structural analysis revealed how the biomass reshapes the material from the inside out. X-ray diffraction showed that quartz remained the dominant crystalline phase in all compositions, inherited largely from unreacted portions of the diatomite and metakaolin precursors, while a broad diffuse feature between roughly 20 and 35 degrees two-theta confirmed the presence of a poorly ordered aluminosilicate geopolymer matrix. Fourier-transform infrared spectroscopy identified the characteristic Si-O-T asymmetric stretching band near 1016 to 1021 per centimeter, along with hydroxyl and carbonate features, and small shifts in these bands after dye exposure hinted at interactions between methylene blue and the composite surface. Scanning electron microscopy told a more visually striking story: the biomass-free pellet was relatively dense, but increasing water hyacinth content progressively introduced interfacial gaps, larger voids, and interconnected pore channels, particularly in the 2 and 3 percent formulations.

Quantitative measurements reinforced what the micrographs suggested. Apparent porosity rose from 58.57 to 62.03 percent across the series, while water absorption climbed sharply from 58.30 to 79.55 percent, and bulk density fell from 1.22 to about 1.08 grams per cubic centimeter. Nitrogen physisorption on the two endpoint compositions showed that the BET specific surface area of the 3 percent pellet reached 14.843 square meters per gram, roughly 86 percent higher than the 7.986 square meters per gram of the biomass-free control, while total pore volume increased by about 75 percent. In other words, the invasive weed was effectively blowing open the internal architecture of the pellet, creating more pathways and more exposed surface for dye molecules to reach.

Surface charge added a second, electrostatic dimension to the story. Zeta potential measurements at pH 7 showed that all pellets carried negative surface charges, becoming progressively more negative as water hyacinth content increased, from minus 67.3 millivolts for the control to minus 74.9 millivolts for the highest-biomass pellet. The point of zero charge of the best-performing composition was approximately 2.22, meaning that at the pH used in the adsorption experiments the surface was decisively negative and therefore electrostatically attractive to positively charged methylene blue cations. Deprotonated surface hydroxyl groups on the aluminosilicate framework, generating negatively charged siloxide and aluminate sites, are thought to contribute to this favorable electrostatic environment.

The adsorption experiments bore out the design logic. At pH 2, performance was poor, with removal efficiencies between roughly 49 and 54 percent, because the flood of hydrogen ions competed with dye cations for adsorption sites. Performance peaked at pH 4, where the 3 percent pellet removed 77.25 percent of methylene blue with an equilibrium capacity of 19.31 milligrams per gram, and remained high but essentially flat from pH 6 through 10, indicating that electrostatics alone do not govern the process. Kinetic measurements showed rapid initial uptake followed by a gradual plateau between about 800 and 1080 minutes, with 24-hour removal reaching 77.03 percent and a capacity of 19.26 milligrams per gram for the best pellet. Increasing the initial dye concentration from 50 to 250 milligrams per liter lowered the removal percentage from 95.26 to 77.40 percent while raising the per-gram capacity from about 4.76 to 19.35 milligrams per gram, the classic signature of a fixed number of sites being progressively saturated.

Equilibrium data fit the Langmuir isotherm model better than the Freundlich model, with a linearized correlation coefficient of 0.9998 and a maximum monolayer capacity of 22.32 milligrams per gram, while both linearized and nonlinear kinetic analyses consistently favored the pseudo-second-order model. Against the backdrop of published geopolymer adsorbents, the 22.32 milligrams per gram figure is competitive, outperforming lightweight geopolymer-expanded glass composites, metakaolin/slag geopolymers, red mud and rice husk ash systems, and coal gangue-based materials, and landing close to reduced graphene oxide/geopolymer composites, though some fly ash and metakaolin systems report higher capacities. The authors caution that direct comparisons across studies are complicated by differences in material form and experimental conditions, and their pellets carry an inherent mass-transfer penalty because dye molecules must diffuse through the pellet interior rather than contacting a loose powder directly.

That penalty is the price of practicality, and the study is unusually candid about the trade-offs involved. Compressive strength after 28 days of curing fell from 21.5 megapascals for the biomass-free pellet to 9.1, 6.5, and 5.5 megapascals at 1, 2, and 3 percent water hyacinth, because the fibrous additive and its interfacial discontinuities disrupt the continuity of the load-bearing geopolymer matrix. The modest gain in equilibrium capacity at the highest biomass loading does not fully compensate for the substantial loss of mechanical robustness, so the researchers suggest that an intermediate water hyacinth content may offer the best balance for applications where pellets must survive handling. Reusability testing over five adsorption-desorption cycles showed another honest limitation: removal efficiency declined to about 33 percent of its initial value by the fifth cycle, even though the pellets retained roughly 99 percent of their mass, pointing to a need for improved regeneration protocols.

What makes this work resonate beyond its numbers is the circular economy story it tells. Water hyacinth is a global nuisance, clogging waterways, blocking navigation, and starving aquatic ecosystems of light and oxygen, yet here its residue becomes a functional ingredient in a low-cost ceramic adsorbent built from abundant local minerals. The study also models a kind of scientific honesty that is increasingly valued in materials research: rather than claiming a single dominant mechanism, the authors attribute dye uptake to coupled effects, including electrostatic attraction to the negatively charged surface, possible hydrogen bonding through hydroxyl-containing groups, and improved pore accessibility, while explicitly declining to claim mechanisms, such as pi-pi interactions, that their characterization could not verify. They note that methylene blue served only as a model cationic dye, and that real textile wastewater, with its mixtures of dyes, salts, and organic matter, will pose stiffer competitive challenges. Future work on mixed-pollutant systems, thermodynamic analysis, and regeneration chemistry will determine whether these weed-powered pellets can graduate from elegant laboratory concept to working technology for the dye-polluted rivers that need them most.

Subject of Research: Pelletized diatomite-based geopolymer composites incorporating water hyacinth biomass for the adsorptive removal of methylene blue dye from wastewater

Article Title: Pelletized diatomite-based geopolymer-water hyacinth composites for methylene blue adsorption: insights into structure-property-performance relationships

Article References: Thammarong, S., Zhang, W., Pimpha, N., Saenkam, K., Boontakam, W., Tandorn, S., Randorn, C., Srichumpong, T., Pengpat, K., & Rujijanagul, G. (2026). Pelletized diatomite-based geopolymer-water hyacinth composites for methylene blue adsorption: insights into structure-property-performance relationships. Results in Chemistry, 31, Article 103923. https://doi.org/10.1016/j.rechem.2026.103923

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103923

Keywords: geopolymer, water hyacinth, diatomite, methylene blue, adsorption, wastewater treatment, dye removal, metakaolin, porous materials, biomass composites, isotherm modeling, mechanical strength