The team, led by Yanfu Zhao and Hongtu Xiu of China Communications Construction Company First Highway Engineering Bureau Group, together with colleagues at Guizhou University and Beibu Gulf University, prepared cube-shaped cement mortar specimens measuring 70 by 70 by 70 millimeters. The mix was deliberately simple: Portland cement, standard sand and water in a mass ratio of 2:1:0.4, with no coarse aggregate at all. That choice matters, because it means the results describe mortar rather than structural concrete, and the authors are careful not to overreach. After casting, the specimens were demolded within 24 hours and cured for 28 days at 20 degrees Celsius and 95 percent relative humidity, giving the cement paste time to develop its full hydration skeleton before any thermal punishment began.

The heating protocol was methodical. Specimens were placed in a rapid-heating resistance furnace and raised at a steady 6 degrees Celsius per minute to one of six target temperatures: room temperature, 100, 200, 300, 400 or 500 degrees Celsius. Once the target was reached, the temperature was held constant for two hours, ensuring the interior of each cube experienced the same thermal exposure as its surface. Then came the experimental fork in the road. One group of specimens was dropped into a water tank for rapid cooling, while its twin was left to cool naturally in the surrounding air. For each temperature and cooling combination, three independent specimens were tested, and the reported mechanical values represent the means of those replicates.

With the specimens cooled, the researchers moved to the heart of the study: direct shear testing. Each cube was mounted in a rock mechanics system capable of applying up to 500 kilonewtons of horizontal load. The apparatus uses a shear box in which the upper half can slide horizontally while the lower half is fixed. Before any shear force was applied, a constant normal stress of 1 megapascal was pressed onto the specimen, simulating the confining pressure a material layer might experience in a real structure. Only then was the shear load ramped up until failure. The resulting stress-displacement curves all shared a recognizable anatomy: an initial compaction stage, a linear elastic stage, an elastic-plastic stage, and finally the post-peak descent into fracture.

The most striking result emerged from the air-cooled series. Peak shear stress and shear modulus did not simply fall as temperature rose. Instead, both parameters climbed with increasing temperature and reached a local maximum near 300 degrees Celsius, after which they collapsed. The shear modulus of air-cooled specimens heated to 300 degrees was a remarkable 78 percent higher than that of untreated material — a counterintuitive boost for a substance that most engineers assume only degrades with heat. Above that threshold, however, the decline was cliff-like. The authors stress that this apparent strengthening is condition-dependent rather than a universal thermal hardening effect, and they interpret it cautiously as a temporary reduction in mechanically active defects rather than proof of a unique strengthening mechanism.

Water-cooled specimens told a far grimmer story. Their peak shear stress decreased monotonically with temperature, a relationship the researchers could capture with a simple linear fit, and their shear modulus rose only slightly up to 100 degrees before declining linearly to just 22 percent of the untreated value at 500 degrees Celsius. At every temperature, the water-quenched material was weaker and more plastic than its air-cooled counterpart, deforming gradually rather than failing in the sudden brittle manner seen in the 300-degree air-cooled group, which exhibited the greatest brittleness of all. The message is unambiguous: thermal shock during rapid cooling inflicts additional, measurable damage on top of whatever the heating itself caused.

To understand why, the team listened to the material literally. Four acoustic emission sensors, coupled to the specimen surface with vaseline and calibrated by a pencil-lead-break test, recorded ultrasonic bursts at a 40-decibel threshold while the shear load was applied. In untreated specimens, the acoustic signature followed a clear two-stage pattern: a quiet, stable pre-peak phase during which cohesion in the cement matrix resisted the load, followed by an explosive post-peak surge as microcracks in the matrix and at the paste-sand interfaces linked up into a continuous shear fracture surface. After the peak, intense but decaying emissions continued as the two halves of the specimen ground against each other in frictional sliding, shedding debris from the fracture faces.

The acoustic records from heated specimens revealed something unexpected. In the 200- and 300-degree air-cooled groups, pre-peak acoustic activity was almost entirely absent, and cumulative event counts fell well below those of untreated specimens. Scanning electron microscopy offered a possible explanation: the shrinkage microcracks that normally pepper the paste-sand interface in cured mortar appeared narrower, or even vanished, after moderate heating. Differential thermal expansion and the removal of moisture may have pressed the cement paste into tighter contact with the sand grains, temporarily quieting the defects that would otherwise crack and pop under load. The authors are careful to note that SEM cannot directly quantify bond strength and that no phase-composition or pore-structure measurements were performed, so this mechanism remains a plausible interpretation rather than a verified conclusion. Above 400 degrees, the picture reversed: thermal microcracking spread through the paste and interfaces, and small acoustic events returned even before the peak load.

The microscopy also settled a question about where the final fracture travels. Post-failure surfaces showed most sand particles still embedded in the cement paste, with only some grains debonded or pulled out, leaving pits behind. There was no evidence of the shear plane slicing extensively through sand particles themselves, even though at 500 degrees thermally induced cracks had appeared locally within some grains. The macroscopic shear localization, in other words, follows the path of least resistance: through the cement paste matrix and along the paste-sand interfaces that bind the composite together. That detail matters for engineers, because it identifies the interfacial transition zone — the weakest link in cementitious materials — as the region where fire damage concentrates its attack.

The physics of water cooling explains the extra deterioration. When a hot specimen meets cold water, its surface temperature drops almost instantly while the interior remains hot, creating a steep thermal gradient. The chilled exterior tries to contract but is restrained by the hot interior, generating transient tensile stresses at the surface. Once those stresses exceed the material’s tensile strength, surface cracks open, and water then penetrates through them, softening the forces between cement gel particles and further eroding load-bearing capacity. The researchers’ stress analysis predicts that shrinkage cracking should concentrate along particular planes of the cube — exactly where the experiments showed it did. For post-fire assessment, the practical implication is that inspectors must reconstruct not only the peak temperature a structure experienced but also how it was cooled, since a water-quenched element may be significantly more damaged than an identical one that cooled in air. The results provide a material-level reference for evaluating repair mortars, cementitious joints and other interface-dominated regions after fire, though the authors caution that their findings, based on mortar without coarse aggregate and a single normal stress of 1 megapascal, should not be directly generalized to structural concrete. Future work with X-ray diffraction, thermogravimetric analysis and computed tomography will be needed to trace the full three-dimensional evolution of pores and cracks through realistic fire-and-cooling histories.

Subject of Research: Effects of elevated temperature and cooling method on the shear behavior and microstructural damage of cement mortar

Article Title: Shear behavior of cement mortar after exposure to elevated temperatures under different cooling conditions

Article References: Shear behavior of cement mortar after exposure to elevated temperatures under different cooling conditions. (n.d.). https://doi.org/10.3389/fbuil.2026.1949325

Image Credits: AI Generated

DOI: 10.3389/fbuil.2026.1949325

Keywords: cement mortar, elevated temperature, cooling method, direct shear, acoustic emission, scanning electron microscopy, thermal shock, fire damage, shear modulus, microcracking, construction materials, post-fire assessment

The research, led by Phani Prasanthi together with B. Raghu Kumar, U. Koteswara Rao, and T. Srinag, presents an integrated framework that weaves together three complementary strands of investigation: physical tensile testing, finite element simulation, and Arrhenius-based kinetic modeling. The goal was not simply to measure how carbon fiber-reinforced polymer composites weaken under heat, but to build a predictive pipeline that can forecast both strength loss and service life across a wide range of operating temperatures, including conditions that were never directly tested in the laboratory.

The experimental backbone of the study consisted of tensile tests conducted at four temperatures: room temperature, 50 degrees Celsius, 80 degrees Celsius, and 100 degrees Celsius. These are not exotic conditions. Components under an aircraft hood, near engine bays, or in sun-exposed automotive structures routinely experience thermal environments in this range, which makes the findings directly relevant to real-world design decisions. The tests were designed to capture the thermo-mechanical behavior of the composites as the polymer matrix that binds the carbon fibers together begins to soften and degrade.

The results were striking. Compared with room-temperature performance, tensile strength fell by 33.33 percent at 50 degrees Celsius, by 61.92 percent at 80 degrees Celsius, and by 57.94 percent at 100 degrees Celsius. The non-monotonic pattern, in which the drop at 100 degrees Celsius was slightly smaller than at 80 degrees Celsius, underscores how complex the underlying degradation mechanisms can be. The polymer matrix is the weak link in this story: carbon fibers themselves retain their strength at these temperatures, but the epoxy or similar resin surrounding them loses stiffness and load-transfer capability as thermal energy disrupts its molecular network. Once the matrix can no longer grip the fibers effectively or transfer stress between them, the composite as a whole fails far below its nominal capacity.

What makes the new work more than another set of measurements is the second pillar of the framework: finite element simulation. The team built numerical models of the tensile tests and calibrated them against the experimental data. The simulations tracked the experiments closely, with prediction errors below 5 percent at room temperature and at 50 degrees Celsius. That level of agreement matters because it establishes the model as trustworthy enough to extrapolate. Having validated the simulation against real data at the lower temperatures, the researchers then used it to predict tensile behavior all the way up to 200 degrees Celsius, a regime where direct testing becomes more difficult and more expensive.

This experimental-to-numerical handoff is a pattern increasingly common in materials engineering, and it addresses a genuine bottleneck. Physical testing at every temperature of interest would demand dozens of specimens, environmental chambers, and weeks of laboratory time. A validated simulation, by contrast, can sweep through a temperature range in hours and flag the conditions that deserve closer experimental scrutiny. In safety-critical fields such as aerospace, where certification authorities demand evidence rather than intuition, a simulation that has been anchored to experimental reality provides exactly the kind of defensible evidence that design reviews require.

The third pillar pushes the work from static prediction into the realm of lifetime forecasting. The researchers employed an Arrhenius kinetic model, a mathematical approach with roots in chemical kinetics that describes how reaction rates accelerate exponentially with temperature. Originally developed to characterize the temperature dependence of chemical reactions, Arrhenius modeling has become a standard tool for predicting the thermal aging and degradation of polymers. In this study, the team used it to establish a quantitative relationship between thermal degradation kinetics and the degradation of tensile strength, effectively linking the speed of molecular-level damage to the macroscopic property that engineers care about most.

The practical payoff of that link is service life prediction. By fitting the kinetic model to the strength data, the framework can estimate how long a composite component will retain adequate strength when held at a given elevated temperature, rather than merely reporting a single strength value measured after an arbitrary exposure. This is the kind of information that maintenance planners and structural designers actually need: not just how strong the material is today, but how strong it will be after years of service in a hot environment. The authors position the integrated framework as a reliable and efficient methodology for predicting tensile strength degradation and service life across a wide range of operating temperatures, supporting both design and long-term reliability assessment in high-temperature applications.

The broader context makes the contribution timely. Carbon fiber composites are expanding into new territory, from wind turbine blades that bake in the sun for decades to electric vehicle battery enclosures that must survive thermal excursions, and the literature has documented repeated concerns about elevated-temperature performance. Previous studies have examined temperature effects on composite mechanics, aging and durability, and failure mechanisms under combined thermal and mechanical loads, but comprehensive frameworks that unite experiment, simulation, and kinetic lifetime modeling in a single validated pipeline remain comparatively rare. The new study also connects to a wider engineering tradition: damage mechanisms and life assessment of high-temperature components have been studied in metals for decades, and this work extends similar predictive logic to polymer-matrix composites.

There are, of course, boundaries to what the study claims. The data availability statement notes that no datasets were generated or analyzed beyond the study itself, and the reported predictions above 100 degrees Celsius rest on simulation and kinetic extrapolation rather than direct measurement, which is precisely why the validation at lower temperatures was so important. The non-monotonic strength behavior between 80 and 100 degrees Celsius also hints that matrix-dominated failure mechanisms may shift with temperature, a nuance that future experimental work could probe further. Still, the framework’s architecture is deliberately modular: as new experimental data arrives, the finite element model and the Arrhenius parameters can be refined, tightening the predictions over time. For an industry that increasingly stakes safety and performance on materials whose weakest ingredient is the polymer holding them together, a tool that turns scattered test data into a continuous, temperature-resolved map of strength and lifespan is a meaningful step forward. It transforms a question that once required a laboratory and a calendar into a calculation that can be run before the first part is ever manufactured.

Subject of Research: Temperature-dependent tensile behavior and service life prediction of carbon fiber-reinforced polymer composites

Article Title: An integrated experimental–numerical–kinetic framework for predicting the tensile behavior of carbon fiber reinforced composites at different temperatures

Article References: Prasanthi, P., Kumar, B. R., Rao, U. K., & Srinag, T. (2026). An integrated experimental–numerical–kinetic framework for predicting the tensile behavior of carbon fiber reinforced composites at different temperatures. Polymer Bulletin, 83(12), Article 673. https://doi.org/10.1007/s00289-026-06709-7

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06709-7

Keywords: carbon fiber composites, tensile strength, finite element analysis, Arrhenius model, thermal degradation, service life prediction, polymer matrix, elevated temperature, CFRP, aerospace materials, structural reliability, integrated

The research matters because sandwich panels—two thin concrete wythes or steel sheets bonded around a lightweight insulating core—have become a dominant technology in energy-efficient construction. Their popularity stems from fast installation, excellent thermal performance, and reduced lifecycle costs, and building codes increasingly favor them as energy regulations tighten. But the insulation core is not merely filler. It transfers load between the outer layers, maintains composite action, and keeps the wall structurally stable. If heat from a fire passes through the concrete faces and softens the core, the panel’s entire load-transfer mechanism can be quietly undermined long before any visible failure occurs. Despite this, most prior research has focused on fire-resistance ratings and thermal conductivity rather than on how the mechanical properties of the core itself degrade.

The experimental program was unusually comprehensive. The team, led by Abhinav Anand with supervision from Vaibhav Singhal, cut specimens from commercially manufactured blocks of the three materials and subjected them to controlled heating followed by four types of mechanical testing at ambient conditions: compression, three-point flexure, double shear, and tension, all performed on a universal testing machine under displacement-controlled loading according to relevant international standards including EN 826, ASTM C203, EN 12090, and EN 1608. EPS specimens, with a density of 16 kilograms per cubic meter, were heated in a laboratory oven at temperatures from 50 to 80 degrees Celsius. The denser XPS, at 34 kilograms per cubic meter, was tested from 60 to 90 degrees Celsius. Rockwool, at 150 kilograms per cubic meter, was heated in a muffle furnace from 200 all the way to 800 degrees Celsius.

The first striking finding concerned geometry. Beyond 80 degrees Celsius for EPS and 90 degrees Celsius for XPS—temperatures associated with the glass transition of polystyrene, where polymer chains gain mobility and the material loses rigidity—the foams physically warped and bulged. EPS contracted dramatically, shrinking 28 percent in thickness, while XPS deformed anisotropically, expanding on some faces by more than 11 percent while contracting on others. At that point the materials could no longer sustain mechanical loading at all, making further testing impractical. Rockwool, by contrast, showed no melting or distortion even at 800 degrees Celsius, though specimens became noticeably softer, fluffier, and slightly discolored above 200 degrees Celsius—early signs that the organic binder gluing its basaltic fibers together was beginning to break down.

The compression results revealed a subtle hierarchy. EPS lost compressive strength progressively, dropping about 13 percent at 50 degrees Celsius and roughly 32 percent at 80 degrees Celsius, while its initial elastic modulus fell by nearly 48 percent. XPS proved remarkably resilient in compression, losing under 1 percent of compressive strength even at 70 degrees Celsius and only about 9 percent at 90 degrees—yet its elastic modulus still collapsed by 47 percent at the highest temperature, signaling irreversible damage to the closed-cell structure even when peak strength appeared intact. Rockwool told the most dramatic story: minor losses up to 400 degrees Celsius, then a catastrophic 78 percent strength reduction at 600 degrees and over 90 percent at 800 degrees, where the response was governed by loose fiber compaction rather than any true structural resistance, following near-complete burnout of the organic binder.

Flexural and shear tests exposed even greater vulnerabilities. EPS flexural strength fell by 20 percent at 80 degrees Celsius, with stiffness plummeting 55 percent. XPS lost about 22 percent of flexural strength and 15 percent of stiffness at 90 degrees. Rockwool, however, could barely be tested in bending after 400 degrees Celsius: the fibrous matrix delaminated into a loose, fluffy mass that could not support its own weight, with residual flexural strength estimated at a mere 1.57 kilopascals—a 99 percent loss. In shear, the pattern repeated. EPS shear strength dropped 38 percent and its shear modulus 50 percent at 80 degrees; XPS lost 47 percent of shear strength and a striking 73 percent of shear modulus at 90 degrees; and rockwool’s shear capacity fell by more than half at just 200 degrees, reaching an estimated 0.34 kilopascals at 400 degrees, when specimens could no longer even hold the steel loading plates of the test apparatus.

Tensile behavior followed suit, with an important nuance about failure modes. EPS failed brittlely through its core, with cracks propagating along weak inter-bead boundaries, losing 27 percent of tensile strength at 80 degrees Celsius. XPS showed a mixed-mode failure dominated by interfacial debonding near the steel plate boundary, losing about 23 percent of tensile strength at 90 degrees. Rockwool failed progressively through fiber pull-out, rupture, and interlayer delamination—a ductile, distributed damage process—but its tensile strength collapsed by more than 90 percent at 400 degrees, at which point a specimen failed immediately under the self-weight of the test assembly alone. Across all four loading modes, tensile and shear properties consistently deteriorated faster than compressive ones, indicating that heat attacks interfacial bonding and cellular connectivity before it destroys bulk load-bearing capacity.

The overall comparison upends conventional fire-safety intuition. Within their survivable temperature ranges, the polymeric foams kept strength losses below 50 percent, because they were tested below their glass transition points where softening occurs but cellular geometry survives. Rockwool, despite never distorting, suffered strength and stiffness reductions exceeding 90 percent in most loading modes because its mechanical integrity depends almost entirely on an organic binder that burns away between 300 and 400 degrees Celsius. In other words, the material that best resists fire in the visible sense—no melting, no dripping, no combustible gases—is also the one whose structural contribution vanishes most completely. EPS and XPS, meanwhile, released combustible gases and warped at relatively modest temperatures, yet retained a larger fraction of their mechanical function within the ranges they could tolerate.

The authors emphasize that these residual-property datasets fill a critical gap for engineers and modelers. The measurements can support post-fire performance assessment, inform the selection of insulation cores for precast concrete sandwich panels, and provide calibration data for numerical models predicting how panel structures behave under thermal loading. The team also notes an important limitation: only a single commercial density of each material was tested, and since density strongly influences stiffness, strength, and thermal response, broader parametric studies will be needed to develop generalized design equations. For now, the message for the construction industry is clear and slightly uncomfortable—fire resistance and residual structural performance are not the same property, and the non-combustible hero of building insulation may be the first to quietly stop doing its structural job when the heat rises.

Subject of Research: Residual mechanical properties of EPS, XPS, and rockwool insulation materials after elevated temperature exposure

Article Title: Residual mechanical properties of EPS, XPS, and rockwool insulation materials after elevated temperature exposure

Article References: Anand, A., & Singhal, V. (2026). Residual mechanical properties of EPS, XPS, and rockwool insulation materials after elevated temperature exposure. Results in Engineering, 32, Article 113053. https://doi.org/10.1016/j.rineng.2026.113053

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113053

Keywords: EPS, XPS, rockwool, insulation materials, sandwich panels, elevated temperature, fire safety, compressive strength, shear modulus, precast concrete, thermal degradation, structural engineering

The motivation is twofold. Cement production is one of the most energy-intensive industrial processes on the planet, responsible for an estimated 7 to 8 percent of global anthropogenic carbon dioxide emissions, while concrete itself is the most widely consumed manufactured material on Earth, with annual usage exceeding 4 billion metric tons. Replacing even a modest fraction of cement with an industrial by-product therefore carries enormous environmental leverage. At the same time, self-compacting concrete, first developed in Japan in the late 1980s, has become a favored technology for densely reinforced and geometrically complex structures because it flows under its own weight and compacts without vibration. Its precise mix design requirements make it particularly receptive to supplementary cementitious materials such as fly ash, slag, and silica fume, which have long been used to cut cement content. Coal slurry powder, however, has remained largely unexplored, especially at high temperatures.

The raw material in this study was air-dried and ball-milled before use, yielding a powder with a specific surface area of roughly 25 to 30 square meters per gram and a specific gravity of 2.35. X-ray fluorescence analysis revealed a predominantly siliceous-aluminous composition, containing approximately 35 to 45 percent silicon dioxide, 8 to 12 percent alumina, 4 to 6 percent iron oxide, and 2 to 4 percent calcium oxide, with the combined silica, alumina, and iron oxide content exceeding 50 percent. The loss on ignition was 13.9 percent, a figure the author treats cautiously because it may include volatile components beyond residual carbon. Importantly, the study stops short of classifying the powder as a confirmed pozzolan, since a standardized pozzolanic activity index and quantitative mineral-phase analysis were not performed; its contribution is interpreted as physical filler action combined with possible secondary reactions.

The experimental program replaced ordinary Portland cement with coal slurry powder at 0, 10, 20, and 30 percent by mass, keeping the total binder content constant at 450 kilograms per cubic meter and the water content at 180 kilograms per cubic meter, for a constant water-to-binder ratio of 0.40. Because the cement fraction shrank as replacement increased, the effective water-to-cement ratio rose from 0.40 in the control to 0.571 in the 30 percent mixture, a detail that helps explain the strength reductions observed at higher dosages. Fresh concrete properties were assessed with slump-flow, V-funnel, and L-box tests following European guidelines for self-compacting concrete. All mixtures fell within the SF2 slump-flow class, with values declining from 720 millimeters for the control to 660 millimeters at 30 percent replacement, while V-funnel times rose from 8.2 to 10.4 seconds and L-box passing ratios dropped from 0.98 to 0.90, all still within acceptable limits thanks to mixture-specific superplasticizer adjustment.

The hardened results told a nuanced story. At ambient temperature, the control mix reached compressive strengths of 30.3, 45.29, and 57.1 megapascals at 7, 28, and 56 days respectively, while the 30 percent replacement mixture managed only 19.7, 29.44, and 37.1 megapascals at the same ages, reflecting straightforward cement dilution. Splitting tensile strength followed the same pattern, falling from 5.64 megapascals in the control at 28 days to 3.67 megapascals at 30 percent replacement. Yet the study’s statistical analysis, a two-way analysis of variance on 28-day compressive strength, showed that exposure temperature was actually the dominant factor controlling performance, with a partial eta squared of 0.993, compared with 0.964 for replacement level and 0.791 for their interaction. Coefficients of variation remained below 6 percent across all conditions, indicating solid experimental repeatability.

Thermal exposure was conducted in a programmable furnace at a deliberately slow heating rate of 2 degrees Celsius per minute, with four-hour holds at 300, 600, and 900 degrees Celsius followed by gradual cooling. The author is careful to note that this protocol characterizes material-level degradation rather than reproducing a standardized structural fire test such as ISO 834 or ASTM E119. At 300 degrees Celsius, strength losses were modest, around 8.5 to 8.6 percent. At 600 degrees, all mixtures lost roughly 41 to 43 percent of their strength as calcium hydroxide decomposed and the calcium silicate hydrate gel began to break down. At 900 degrees, only about one-third of the original ambient strength remained in every mixture; the 28-day control retained 14.90 megapascals and the 30 percent mix just 9.69. Crucially, the proportional losses were nearly identical across all replacement levels, at roughly 67 percent, meaning the coal slurry powder did not improve percentage strength retention at extreme temperatures.

Where the moderate replacement levels genuinely shone was in durability and microstructure. At ambient conditions, the 20 percent mixture absorbed less water than the control, 3.6 percent versus 4.2 percent, showed lower sorptivity at 0.09 versus 0.12 millimeters per square root of minute, passed a lower chloride charge in the rapid chloride permeability test, 2200 versus 2800 coulombs, and exhibited higher electrical resistivity at 16.8 versus 12.5 kilohm-centimeters. These gains are consistent with improved particle packing and possible secondary reactions that reduced pore connectivity. By contrast, the 30 percent mixture performed worse than the control on every transport measure, confirming that excessive substitution dilutes the cementitious phases. Scanning electron microscopy reinforced the picture: at 300 and 600 degrees, the 10 and 20 percent mixtures showed less cracking and better preserved interfacial transition zones than the control, while the 30 percent mix deteriorated fastest, and at 900 degrees all samples suffered severe damage.

The multi-technique microstructural analysis traced the degradation mechanisms in detail. Energy-dispersive X-ray analysis showed that the control’s calcium-to-silicon mass ratio of about 2.17 at ambient temperature dropped to roughly 0.85 to 0.95 with 10 to 20 percent replacement, reflecting the influx of silica-rich phases, then climbed to above 4 in all mixes at 900 degrees as silicate hydration products were destroyed and calcium-rich decomposition products concentrated. Fourier-transform infrared spectroscopy documented the progressive loss of hydroxyl and water-related bands, while thermogravimetric analysis recorded total mass losses of 6 to 8 percent at low temperatures, 18 to 22 percent after intermediate degradation, and 30 to 40 percent across the full range, with distinct events marking water evaporation below 200 degrees, portlandite dehydroxylation at 400 to 500 degrees, and carbonate decomposition between 650 and 800 degrees. X-ray diffraction confirmed the near-complete disappearance of calcium hydroxide and calcium carbonate peaks and the collapse of the amorphous binding phase at 900 degrees.

The practical takeaway is a carefully bounded one. Within the conditions investigated, 10 to 20 percent coal slurry powder offers a favorable balance: it cuts cement consumption by up to 90 kilograms per cubic meter at the 20 percent level while maintaining acceptable mechanical performance and delivering the clearest durability benefits of any mixture tested. The author emphasizes, however, that these material-level results do not establish a structural fire-resistance rating, and that fire-critical load-bearing applications would require standardized structural fire testing, realistic heating curves, applied loading, and appropriate fire protection measures. The study also flags important caveats for real-world deployment: only a single coal-processing source was examined, slurry composition varies widely with geology and beneficiation methods, and coal-processing residues may contain environmentally relevant trace metals, so total elemental analysis and standardized leaching tests should precede large-scale structural use, particularly where concrete may contact groundwater.

Future work, the study suggests, should tackle long-term durability under chloride exposure, freeze-thaw cycling, and chemical attack, explore blending coal slurry powder with other supplementary materials, apply advanced tools such as nano-indentation and in-situ thermal characterization, and conduct full-scale structural testing and life-cycle assessments that account for drying, grinding, and transportation of the powder. Until then, the research stands as a compelling proof of concept that one of coal mining’s most troublesome waste streams can, at moderate dosages, become a functional ingredient in high-performance concrete, turning an environmental liability into a small but meaningful wedge against the cement industry’s carbon footprint.

Subject of Research: Use of coal slurry powder as a partial cement replacement in self-compacting concrete evaluated for mechanical, durability, and elevated-temperature performance

Article Title: Valorization of coal slurry powder in self-compacting concrete: Mechanical, durability, and elevated-temperature performance

Article References: Almutairi, A. (2026). Valorization of coal slurry powder in self-compacting concrete: Mechanical, durability, and elevated-temperature performance. Case Studies in Construction Materials, 25, Article e06537. https://doi.org/10.1016/j.cscm.2026.e06537

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06537

Keywords: coal slurry powder, self-compacting concrete, cement replacement, sustainable construction, elevated temperature, durability, compressive strength, microstructure, supplementary cementitious materials, thermal degradation, chloride permeability, carbon emissions

The research, conducted by Fatih Kantarci and Moncef L. Nehdi, centers on geopolymer concrete, an alkali-activated alternative to Portland cement concrete that is synthesized from industrial by-products rich in aluminum and silicon, such as blast furnace slag, metakaolin, and fly ash. When these precursors are mixed with highly alkaline solutions like sodium hydroxide, a chemical process called geopolymerization forms three-dimensional Si-O-Al-O polymeric gels that bind aggregates into a solid mass. Depending on the precursor and activator chosen, geopolymer binders can cut CO2 emissions by up to 80 percent compared with Portland cement, while saving roughly 60 percent of the energy and reducing production costs by about 25 percent. Geopolymer concretes have already found their way into road pavements, precast elements, and fire-resistant construction in the United States, Australia, Europe, and India.

Like most cementitious materials, however, geopolymer concrete is inherently brittle and prone to cracking under moderate loads or shrinkage stresses. The established remedy is fiber reinforcement, which enhances crack resistance, tensile strength, ductility, and impact performance while redistributing stresses within the matrix. Among the many fiber types available, the researchers selected glass fiber for its affordability, ease of manufacture, corrosion resistance, and high tensile strength of 1300 megapascals. The glass fibers used in the study were just 6 millimeters long and 15 micrometers in diameter, with an elastic modulus of 72 gigapascals and, crucially, a melting point of approximately 850 degrees Celsius, meaning they retain structural stability throughout the temperature range examined.

The experimental program began with a careful optimization of the geopolymer mix itself. Blast furnace slag from a local plant, with a specific gravity of 2.84 and a cement-like fineness, served as the primary precursor at a dosage of 400 kilograms per cubic meter. The team varied the sodium hydroxide activator concentration across 10, 12, and 14 molar solutions and tested alkali activator solution-to-binder ratios of 0.50 and 0.60. Compressive strength measurements at 7, 28, and 90 days revealed a clear optimum: strength increased as the sodium hydroxide concentration rose to 12 molar, then declined at 14 molar. The researchers attribute the initial gain to higher alkalinity, which dissolves silicon and aluminum links in the raw precursor to form aluminosilicate gels, while the decline at 14 molar reflects inhibited condensation reactions of silicate species and the precipitation of geopolymer gels that ultimately weaken the matrix. Scanning electron microscopy confirmed the story, showing a dense, compact microstructure with low porosity in the strongest mixes and abundant large pores and cracks in the weakest.

With the optimum production parameters established at 12 molar sodium hydroxide and a 0.60 activator-to-binder ratio, the team incorporated glass fibers at volume fractions of 0.3, 0.6, and 0.9 percent. Notably, the concrete was cured entirely under ambient laboratory conditions at 23 degrees Celsius and 55 percent relative humidity, with no steam or heat curing, removing a major barrier to casting geopolymer concrete on real construction sites. After 90 days of curing, the specimens were exposed to temperatures of 150, 300, 450, 600, and 750 degrees Celsius for one hour in a furnace heated at roughly 2 degrees Celsius per minute, then cooled under two contrasting regimes: gradual air cooling inside the opened furnace, or rapid immersion in room-temperature water, simulating the thermal shock that firefighting operations inflict on burning structures.

The results reveal a nuanced interplay between fiber content, temperature, and cooling method. Glass fibers improved compressive strength in both heated and unheated specimens, with the optimum at 0.6 percent by volume. At this dosage, fibers wrapped in geopolymer gel bond strongly to the matrix, bridging cracks, reducing stress concentrations at crack tips, and retarding crack propagation. The residual compressive strength of the fiber-reinforced samples actually increased up to 150 or 300 degrees Celsius, a phenomenon attributed to polycondensation and further densification of the tetrahedral aluminosilicate gels as moisture evaporates, before declining at higher temperatures. Remarkably, after exposure to 750 degrees Celsius, the water-cooled specimen containing 0.6 percent glass fiber retained a compressive strength approximately 33 percent higher than the plain, fiber-free samples. Beyond 450 degrees Celsius, however, the mismatch in thermal expansion coefficients between glass fibers and the geopolymer matrix generated interfacial stresses and microcracks, while partial softening of the fibers, dehydration of the gels, and thermal phase transformations further eroded strength.

The cooling regime proved to be a decisive variable. Water-cooled samples consistently exhibited lower residual compressive and flexural strengths than their air-cooled counterparts, because the steep temperature gradients during rapid quenching induce thermal shock, microstructural damage, and an elevated risk of explosive spalling. Flexural strength, which is particularly sensitive to crack initiation and propagation, benefited even more visibly from fiber reinforcement, since the three-dimensionally dispersed fibers direct crack paths and transfer stresses through a bridging effect that preserves specimen integrity. At all temperatures, the 0.6 percent fiber content delivered the highest flexural values, and the relative improvement from fiber addition was more pronounced in flexure than in compression, underscoring the dominant role of crack bridging in bending behavior.

Complementary measurements of weight loss and water absorption traced the progressive thermal deterioration of the material. Weight losses remained modest at 150 and 300 degrees Celsius, driven by the evaporation of free and absorbed water, but increased sharply after 450 degrees Celsius as thermal stress generated microcracks, and again at 750 degrees Celsius, where thermo-chemical damage degraded the geopolymer gel itself. The fiber-free air-cooled specimen lost 1.3 percent of its mass at 150 degrees Celsius but 7.1 percent at 750 degrees Celsius, roughly a five-and-a-half-fold increase, while 0.3 and 0.6 percent fiber additions reduced these losses by preserving microstructural integrity. Water absorption told a parallel story: values stayed nearly unchanged up to 450 degrees Celsius thanks to the dense matrix, then climbed as thermally induced shrinkage and thermal-shock microcracking opened new transport pathways. The fiber-free water-cooled sample doubled its water absorption from 4.3 to 8.6 percent after exposure to 750 degrees Celsius. Interestingly, the highest fiber dosage of 0.9 percent proved counterproductive, increasing water absorption because of poor workability, uneven fiber dispersion, and fiber balling, a reminder that more fiber is not always better.

Visual and microstructural examinations completed the picture. Sample surfaces brightened to a light brown up to 600 degrees Celsius and darkened to brown-black at 750 degrees Celsius, a coloration attributed to the gehlenite phase identified by X-ray diffraction, which also detected calcium silicate, calcium oxide, akermanite, and ilvaite. Crucially, the glass fibers did not melt even at 750 degrees Celsius, and no specimen fragmented, chipped, or disintegrated under either cooling regime, although water-cooled samples displayed more surface cracks. Scanning electron microscopy after 750 degrees Celsius showed that the fibrous air-cooled sample retained a dense, compact microstructure, while the non-fibrous water-cooled sample exhibited large cracks and spherical pores, with fiber-matrix debonding and increased microcrack density explaining the measured strength losses.

The study’s conclusions carry practical weight for the construction industry’s decarbonization ambitions. An ambient-cured, slag-based geopolymer concrete reinforced with 0.6 percent glass fiber emerges as a promising candidate for fire-resilient structural applications, provided that workability and fiber dispersion are carefully controlled. The findings also deliver a clear warning for fire engineering: the way a structure cools after a fire matters nearly as much as the fire itself, with rapid water quenching inflicting measurable thermal-shock damage that gradual air cooling avoids. The authors point toward future research on long-term durability under diverse service environments and on extending the approach to other fiber types and cooling scenarios, steps that could help carry geopolymer composites from the laboratory into the load-bearing skeleton of sustainable cities.

Subject of Research: Elevated-temperature resistance of glass fiber-reinforced geopolymer concrete under different cooling regimes

Article Title: Elevated-temperature resistance of glass fiber-reinforced geopolymer concrete under different cooling regimes

Article References: Kantarci, F., & Nehdi, M. L. (2026). Elevated-temperature resistance of glass fiber-reinforced geopolymer concrete under different cooling regimes. Cleaner Engineering and Technology, 34, Article 101311. https://doi.org/10.1016/j.clet.2026.101311

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101311

Keywords: geopolymer concrete, glass fiber, elevated temperature, fire resistance, cooling regime, thermal shock, blast furnace slag, compressive strength, flexural strength, sustainable construction, alkali-activated materials, microstructure