The researchers used weathered coal gangue that had been stored in the open air for two years at the Jilin Coal Energy Reserve Base in China. The particles were light gray, rough, loosely structured and unevenly graded, with most concentrated in the 9.5–19.0 mm range. Untreated material had a crushing index of 23.96%, above the 20% limit for Class II crushed stone specified in GB/T 14685-2022, and was therefore considered unsuitable for direct use as a pavement-concrete aggregate. Its other measured properties were a 28.61% Los Angeles wear rate, 24.86% firmness index, 84.32 kgf/mm² Vickers hardness and 7.32% aggregate impact value.

The treatment combined a physical cement coating with chemical hardening. Cement paste was prepared at a water-to-cement ratio of 0.75, and 1.5% magnesium aluminum silicate was added to stabilize the paste and suppress bleeding. Weathered gangue was mixed into the paste for two minutes, soaked for 30 minutes, removed and air-dried for two days. A water-based lithium-based curing agent, diluted at a curing-agent-to-water ratio of 1:2, was then sprayed evenly over the particle surfaces. After another 30 minutes of room-temperature drying, the material was cured for 28 days. The agent’s lithium silicate can react with calcium hydroxide in the cement coating to form calcium silicate hydrate, while cement reactions can produce calcium silicate hydrate and calcium aluminate hydrate on and beneath the aggregate surfaces.

After consolidation and 28 days of curing, the gangue’s crushing index declined from 23.96% to 16.05%, placing it below the cited Class II threshold. Vickers hardness rose from 84.32 to 141.43 kgf/mm², Los Angeles wear loss fell from 28.61% to 19.88%, and the aggregate impact value declined from 7.32% to 5.66%. These laboratory measurements showed greater hardness and resistance to wear and impact-induced fragmentation. Density increased from 2.4751 to 2.619 g/cm³, while water absorption rose slightly from 4.32% to 4.82%, meaning that the treatment strengthened the particles without removing their porous character.

To examine how particle size affected concrete behavior, the team prepared one natural-stone control and four mixtures in which consolidated weathered gangue progressively replaced conventional aggregate over wider size intervals. The Fuller target gradation contained 0–2.36, 2.36–4.75, 4.75–9.50, 9.50–19.0 and 19.0–31.5 mm fractions. The gangue mixtures cumulatively replaced conventional aggregate through 2.36–4.75, 2.36–9.50, 2.36–19.0 and 2.36–31.5 mm, representing 11.46%, 27.55%, 50.29% and 72.63% of the total aggregate. The 0–2.36 mm fraction was not replaced, and the study did not separately test different replacement ratios within an individual size fraction.

Each mixture and specimen type included four replicates, with reported values and force–displacement data calculated as arithmetic means. According to GB/T 50081-2019, 100 mm cubes were used for compressive and shear testing, 150 mm cubes for splitting tensile testing and 100 by 100 by 400 mm prisms for flexural testing. The pavement mix contained 315 kg/m³ of cement, 120 kg/m³ of water, 1% water-reducing admixture, 632 kg/m³ of fine aggregate and 1,283 kg/m³ of coarse aggregate. Specimens were tested after 28 days, using a loading rate of 0.5 MPa/s for compression and shear and 0.05 MPa/s for splitting tension and flexure.

Under the study’s secondary-road criteria, the maximum admissible replacement extended from 2.36 to 19.0 mm. At that setting, the concrete achieved 27.81 MPa compressive strength, 2.13 MPa splitting tensile strength, 4.67 MPa flexural strength, 2.93 MPa cohesion and an internal friction angle of 66.20°. Replacing only the 2.36–4.75 mm fraction yielded flexural and splitting tensile strengths of 5.24 and 3.13 MPa, compared with 5.22 and 3.08 MPa in the control. Because the splitting-strength difference was only about 1.6% and the error bars overlapped, the researchers interpreted it as essentially unchanged. The 2.36–9.50 mm mixture also retained 5.18 MPa flexural strength, above the study’s heavy- and higher-traffic criterion of more than 5.0 MPa.

Mechanical performance generally weakened as larger gangue fractions entered the concrete. Splitting tensile strength was 2.78 MPa for the 2.36–9.50 mm replacement, 2.13 MPa for 2.36–19.0 mm and 1.52 MPa for replacement through 31.5 mm. The latter two values represented reductions of 30.8% and 50.6% relative to the unreplaced control. Flexural strength fell to 3.44 MPa in the fully replaced mixture, 34.1% below the control. The researchers associated the reductions with the lower strength and higher porosity of coarse gangue, which promoted aggregate fracture and stress concentration. They also observed that gangue absorbed water during curing, potentially lowering the local water-to-cement ratio and strengthening the aggregate–mortar bond.

Failure morphology changed alongside the strength measurements. Natural-aggregate concrete developed an X-shaped fracture that began near the corners and propagated through interfacial transition zones, or ITZs, toward the center. In gangue mixtures, cracks increasingly traveled through the gangue as well as the ITZ and mortar, and the overall response became more plastic. Under full replacement, the outermost large gangue particles failed first, after which damage progressed inward. Splitting-tensile failure displacement decreased from 10.43 mm in the control to 4.19 mm in the fully replaced group, indicating reduced deformation capacity. Cohesion declined from 4.23 MPa in the control to 1.75 MPa at full replacement, while the internal friction angle increased to 71.43°; the authors noted that this occurred alongside deterioration in other mechanical properties.

A two-dimensional finite-element model represented the 100 mm compression specimens with 40,000 CPS4R elements and four material phases: gravel, mortar, consolidated gangue and a weakened ITZ. Simulated compressive strengths exceeded the corresponding laboratory means by 5.61–10.68%. For example, the model estimated 44.62 MPa for the control, compared with a measured mean of 41.32 MPa, and 23.68 MPa at full replacement, compared with 21.41 MPa. The study attributes the difference partly to the idealized model, which does not reproduce specimen unevenness and machine error and cannot fully capture thickness-direction behavior, lateral diffusion or all cracking effects. Despite these limitations, the simulations reproduced the observed shift in failure location and crack path.

At the maximum replacement range of 2.36–19.0 mm, the model indicated that natural aggregate in the 19.0–31.5 mm fraction carried 58.31% of the stress contribution. The corresponding shares were 22.88% for 9.50–19.0 mm, 13.43% for 4.75–9.50 mm and 5.38% for 2.36–4.75 mm. Mean stress was 22.54 MPa in the largest natural-stone fraction, compared with 9.30, 9.77 and 9.68 MPa in the progressively smaller fractions. The analysis supports a gradual replacement strategy under the tested conditions: consolidated weathered gangue can occupy smaller aggregate fractions while the largest conventional stones provide much of the modeled load-bearing capacity. Durability under traffic, repeated loading, environmental exposure and field-scale construction was not evaluated, leaving those questions beyond the evidence presented by this laboratory study.

Subject of Research: Mechanical performance of mining-area pavement concrete containing consolidated weathered coal gangue

Article Title: Mechanical behaviors of weathered coal gangue filled concrete pavement based on surface solidification

Article References: Li, Y., Guo, W., Miao, X., Tao, X., Wang, Q., Zhang, J., Chen, W., & Wei, Z. (2026). Mechanical behaviors of weathered coal gangue filled concrete pavement based on surface solidification. Frontiers in Materials, 13, Article 1954367. https://doi.org/10.3389/fmats.2026.1954367

Image Credits: AI Generated

DOI: 10.3389/fmats.2026.1954367

Keywords: weathered coal gangue, concrete pavement, surface consolidation, lithium silicate, recycled aggregate, compressive strength, flexural strength, failure modes, finite-element simulation, mining infrastructure, Mechanical, behaviors

For the experimental series, the researchers produced biochar through controlled pyrolysis of sisal fibers and incorporated the particles into an epoxy matrix as filler. They then made five laminates containing zero, one, two, three or four layers of sisal mat using the hand lay-up method. Mechanical performance improved incrementally as the number of mat layers increased, with the three-layer formulation recording the highest reported values. The available abstract does not provide numerical results for all five formulations, so the size of the improvement between adjacent samples cannot be determined from the supplied evidence.

The three-layer composite’s elongation value of 5.50% was reported alongside its tensile and flexural strengths, but the abstract does not describe the deformation sequence, failure mode or test conditions. It likewise does not provide individual measurements, error bars or other statistical measures of variation. The study therefore establishes the strongest reported result within this laboratory series, but the supplied material does not show how reproducible that result would be across larger batches, different processing conditions or service environments.

Physical-property measurements showed density rising from 1.10 to 1.31 g/cm3 across the tested material series. At the same time, thermal conductivity decreased from 1.30 to 1.16 W/m K, which the researchers described as improved insulation. These changes were measured properties of the composites, not evidence of a quantified trade-off between reinforcement and heat transfer. The abstract also does not identify which individual formulation produced either endpoint, report measurement uncertainty or compare the thermal performance with conventional fiber-reinforced epoxy systems.

Scanning electron microscopy showed that the sisal-derived biochar was dispersed homogeneously and that adhesion between the sisal fiber and epoxy matrix was strong. The supplied source does not support additional conclusions about load transfer, interfacial defects or the causes of the measured mechanical behavior. By combining sisal fiber mats with particles made from the same plant fiber, the researchers developed a hybrid composite aimed at improving strength and thermal behavior while retaining a sustainability objective. However, the abstract reports no lifecycle assessment, comparison with other composite materials, recycling test or long-term durability measurement, so it does not demonstrate an end-to-end environmental advantage or suitability for a finished engineering structure.

Subject of Research: Laboratory characterization of sisal-fiber and sisal-biochar reinforced epoxy laminates

Article Title: Development and characterization of sustainable hybrid epoxy biocomposites reinforced with sisal fiber mats and sisal-derived biochar particles

Article References: Arunraja, K. M., Lavanya, R., Arunkumar, S., & Senthilkumar, V. (2026). Development and characterization of sustainable hybrid epoxy biocomposites reinforced with sisal fiber mats and sisal-derived biochar particles. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13918-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13918-y

Keywords: sisal fiber, biochar, epoxy composite, biocomposites, tensile strength, flexural strength, thermal conductivity, scanning electron microscopy, sustainable materials, Development, characterization, sustainable

The choice of infrared heating in this study also reflects a deliberate engineering trade-off. Laser-assisted tape placement offers precise, concentrated energy delivery and is well established in aerospace production, but the equipment is expensive and requires careful safety management. Hot-gas torch heating is gentler but less energy-efficient and can be difficult to control across varying layup geometries. An IR lamp sits between these extremes: it delivers radiant energy that can be tuned in intensity, it heats the tow and substrate without physical contact, and the hardware cost is a fraction of that of a laser system. Radiant heating also couples reasonably well with dark carbon fiber surfaces, which absorb infrared radiation efficiently, reducing the amount of energy wasted on the surrounding air. For a material like CF/PC, whose processing temperatures are moderate compared with high-temperature matrices such as PEEK, the IR lamp provides sufficient heat flux without the need for the extreme power densities that laser systems are designed to deliver.

The two parameters isolated in the design of experiments, compaction force and tool temperature, act on consolidation through complementary mechanisms. Compaction force governs the mechanical squeeze flow of the softened polymer at the interface between the newly placed tow and the substrate beneath it. When the matrix reaches a sufficiently low viscosity, pressure from the roller spreads the polymer across surface asperities, displaces entrapped air, and increases the real contact area between layers. Insufficient force leaves interlaminar gaps and voids that act as crack initiation sites under flexural and shear loading. Excessive force, however, can squeeze matrix material out from the tow edges, thin the resin-rich layer at the interface, and in extreme cases damage the fiber architecture or distort the placed tow. Tool temperature, by contrast, controls the thermal boundary condition of the process. A warmer tool reduces the rate at which heat is drawn away from the bond line, extending the time available for polymer diffusion and wetting before the material cools below its processing range. The heat-sink effect documented in prior AFP studies, in which bond quality degrades through the laminate thickness as successive layers cool the growing stack, is directly moderated by tool temperature. A heated tool essentially raises the baseline from which each new layer must be heated, narrowing the thermal gradient that drives heat away from the interface.

The selection of flexural strength and lap-shear strength as the primary response variables is well matched to the failure modes that poor consolidation produces. Flexural testing loads the laminate in a bending configuration that places the outer plies in tension and compression, making the measurement sensitive to interlaminar weaknesses that allow plies to separate or delaminate under the bending-induced shear stresses. Lap-shear testing, in which two overlapping bonded regions are pulled in opposite directions, directly interrogates the quality of the fusion bond between layers. Fractographic examination of the tested specimens by digital microscopy provides the mechanistic link between process parameters and mechanical outcomes: surfaces that fail cohesively through the polymer, leaving polymer residue on both mating faces, indicate that the fusion bond achieved full integrity, whereas clean interfacial separation with exposed fiber surfaces indicates incomplete wetting and bonding. This combination of quantitative mechanical data and qualitative fractography allows the researchers to distinguish between defects that merely reduce stiffness and those that fundamentally compromise the bond.

The demonstration of laying CF/PC tows onto a rotating three-dimensional printed polyetherimide cylindrical mold deserves particular attention, because it addresses one of the persistent practical barriers to AFP adoption. Conventional AFP tooling is typically machined from metal, which is expensive, heavy, and time-consuming to produce for each new geometry. Additively manufactured tooling offers rapid, low-cost production of complex shapes, but it introduces challenges: printed polymers generally tolerate lower surface temperatures than metals, their thermal conductivity is far lower, and their surface finish and dimensional stability under heat can be inferior. Polyetherimide is a high-temperature amorphous thermoplastic with a glass transition temperature well above the processing temperatures needed for polycarbonate, making it a plausible candidate material for a mold that must withstand repeated exposure to IR heating and hot tows. The low thermal conductivity of a polymer mold, which would be a liability in processes requiring rapid heat extraction, may actually be advantageous here, since it reduces the heat-sink effect that pulls thermal energy away from the bond line during placement. Successfully laying tows on such a mold without secondary machining demonstrates a pathway from printed design to consolidated composite part in a single workflow, which is significant for low-volume production, prototyping, and geometrically complex structures such as ducts, fuselage sections, and pressure vessels.

The drone frame application mentioned in the study illustrates the market segment where CF/PC via IR-assisted AFP is most immediately competitive. Unmanned aerial vehicles demand high stiffness-to-weight ratios, moderate mechanical loads, and increasingly, production volumes that exceed what manual layup or autoclave processing can economically deliver. Thermoplastic matrices add further advantages relevant to this sector: they can be welded for assembly and repair, they resist impact damage better than brittle thermoset matrices in many cases, and they can be re-melted at end of life for recycling, an attribute of growing importance as environmental regulation tightens across the automotive and electronics industries where this material was originally targeted by its supplier.

It is worth situating the reported achievement in the broader context of AFP process science. The finding that IR power and robot speed emerged as the most critical parameters from screening is consistent with the fundamental physics of the process: the energy delivered per unit length of tow, which is the ratio of heating power to layup speed, determines whether the matrix reaches the viscosity needed for bonding. Too little energy per unit length leaves the polymer too stiff to flow and wet the substrate; too much energy degrades the matrix through thermal oxidation or chain scission, and can also cause excessive tow sagging and buckling under the compaction roller. The subsequent identification of compaction force and tool temperature as the next most influential parameters reflects the two-stage nature of consolidation: heating first brings the polymer to a processable state, and the combination of pressure and retained heat then determines how completely the polymer flows and bonds before cooling. The comparison of steel and silicone compaction rollers adds a further dimension, since roller compliance affects how pressure is distributed across the tow and how the roller conforms to curved surfaces, which matters greatly for the cylindrical mold demonstration.

The claim that this is the first investigation of an amorphous matrix, specifically CF/PC, using IR-assisted AFP highlights a gap in the literature. Most published AFP parameter studies have concentrated on semi-crystalline aerospace matrices, partly because certification requirements in aerospace have historically favored materials with well-characterized melting behavior and established databases. Extending AFP process knowledge to amorphous, lower-cost matrices broadens the accessible application space toward consumer products, electronics housings, and ground transportation, where cost per kilogram and cycle time weigh more heavily than ultimate temperature capability. The reported demonstration of improved mechanical properties at optimized settings, achieved out-of-autoclave without secondary consolidation, supports the argument that IR-assisted AFP can produce CF/PC laminates of sufficient quality for semi-structural duty, and the combination of a cost-effective heat source, a moderately priced matrix, and additive tooling suggests a manufacturing chain whose economics could favor adoption in industries where autoclave-grade thermoplastic AFP has remained out of reach.

Subject of Research: Infrared-assisted automated fiber placement of carbon fiber-polycarbonate thermoplastic composites

Article Title: Enhanced manufacturing quality of thermoplastic composites through infrared-assisted automated fiber placement

Article References: Venkatesan, C., Ridhwan, M., Zulkifli, F., Gupta, U., & Silva, A. (2025). Enhanced manufacturing quality of thermoplastic composites through infrared-assisted automated fiber placement. Frontiers in Manufacturing Technology, 5, Article 1649798. https://doi.org/10.3389/fmtec.2025.1649798

Image Credits: AI Generated

DOI: 10.3389/fmtec.2025.1649798

Keywords: automated fiber placement, carbon fiber, thermoplastic composites, infrared heating, process optimization, mechanical properties, polycarbonate, in-situ consolidation, flexural strength, lap-shear strength, 3D printed mold, manufacturing

The work, carried out by Ferit Cakir, Pinar Yildirim, and Mohsen Shams, addresses a longstanding problem in structural rehabilitation. Aging concrete and masonry structures often suffer from deteriorated material, insufficient load-carrying capacity, and limited ability to deform without catastrophic failure. Traditional fixes—jacketing with reinforced concrete or steel—work, but they add significant weight and bulk and demand labor-intensive construction. Fiber-reinforced polymer composites have become the elegant alternative: they are corrosion-resistant, add almost no mass, and can be bonded directly onto existing surfaces. Yet each fiber family has its own Achilles heel. Carbon fibers are stiff and strong but fail suddenly and brittlely. Glass fibers stretch further but are less stiff. Aramid fibers, the stuff of bulletproof vests, absorb enormous energy but struggle in compression and degrade under moisture and ultraviolet light.

Hybridization is the attempt to have it all. Rather than relying on a single fiber type, engineers weave or laminate two fiber families together so that a stiff fiber carries load at small deformations while a tougher, more extensible fiber keeps working after damage begins, delaying unstable fracture. The fabrics used in this study take the concept to its finest scale: intraply hybrids, in which carbon, glass, and aramid yarns are interwoven within the same plain-weave layer, not stacked in separate plies. The team tested three combinations—carbon-glass, aramid-carbon, and glass-aramid—each with a nominal areal weight of 200 grams per square meter. Because both fiber families share the same bonded surface, they can participate simultaneously in load transfer and crack control, a property the authors argue makes intraply architecture especially promising for external strengthening of cementitious elements.

The experimental program was disciplined in its symmetry. Each fabric was bonded with a two-component epoxy in three orientations—horizontal, vertical, and diagonal at 45 degrees—producing nine strengthened configurations, each represented by three specimens. Mortar prisms of 40 by 40 by 160 millimeters were tested in three-point bending, 50-millimeter cubes under axial compression, and cured fabric coupons in direct tension, all following the EN 196-1 and ASTM D3039 standards. Unstrengthened reference specimens established the baseline: 6.66 megapascals of flexural strength and 46.29 megapascals in compression. Crucially, the amount of reinforcement was kept identical across orientations, so any difference in performance could be traced to fiber composition and geometry rather than quantity of material.

The tension tests delivered the first surprise. The aramid-carbon fabric pulled along its horizontal aramid direction was the champion, averaging 178.18 megapascals—nearly six times the 30.82 megapascals of the glass-aramid fabric pulled along its weak aramid direction. Intriguingly, carbon was not the strongest direction in either carbon-containing fabric, a sign that yarn count, crimp, and impregnation quality sculpt each fabric’s directional character as much as the fiber chemistry does. In every hybrid, the diagonal coupon fell between the horizontal and vertical results, exactly what the orthogonal weave predicts when both families share the load at 45 degrees. Statistical analysis confirmed that hybrid system, orientation, and their interaction all shaped tensile strength with overwhelming significance.

But it was the structural tests that rewrote the rankings. Every strengthened prism beat the unconfined reference, with flexural strengths climbing from 16.04 to 39.41 megapascals—gains of 141 to 492 percent. The star was not the aramid-carbon fabric but the carbon-glass hybrid laid diagonally, which reached 39.41 megapascals, almost six times the reference. Under bending, cracks rarely travel perfectly straight; they fork and incline as stresses redistribute. Diagonal reinforcement intercepts those wandering crack paths at multiple points, mobilizing both fiber families at once, spreading damage instead of concentrating it in one fracture plane. The researchers observed precisely this behavior: diagonal specimens developed distributed, inclined cracking, while horizontal and vertical layouts produced a single localized crack that the fabric bridged. In fact, within every hybrid system, the horizontal-versus-vertical ranking in bending mirrored the coupon tensile strength of whichever fiber family ran along the prism axis—a satisfying confirmation that post-cracking flexural capacity is governed by the crack-bridging family.

Compression told a very different and humbling story. Here the fabric does not pull across cracks; it acts as a passive corset, restraining the lateral expansion that Poisson effects generate as the mortar core crushes. Only the fiber family wrapped around the circumference matters, and its performance depended on fit rather than raw strength. Just two configurations beat the reference significantly: carbon-glass vertical, at 53.70 megapascals, a 16 percent gain, and glass-aramid horizontal, at 53.51 megapascals, a 15.6 percent gain. Both placed glass yarns in the hoop direction—a telling detail, because glass’s higher failure strain lets the wrap stretch around square corners and follow the dilating core without rupturing prematurely. Meanwhile, every aramid-carbon layout and the vertical glass-aramid layout significantly reduced compressive strength, with the worst case dropping 40.1 percent. The authors attribute the losses to sharp unrounded corners concentrating stress in the fabric, platens already providing passive restraint at the cube ends, and aramid yarns being difficult to impregnate with epoxy, weakening the confining action.

A two-way factorial analysis of variance formalized the pattern. For compressive strength, the interaction between hybrid system and orientation produced the largest effect of the entire study, with a partial eta-squared of 0.928—meaning the benefit of any given orientation is inseparable from the fibers it positions. The same held for tension and flexure. The researchers are careful about terminology: without single-fiber control fabrics, they cannot claim a quantified synergistic hybrid effect against a rule-of-mixtures baseline, so the differences among fabrics are interpreted as effects of hybrid composition—the specific fiber combinations, proportions, and arrangements within the weave—rather than proven synergy. This candor does not diminish the practical punch of the findings; it sharpens them.

The broader message is one that materials data sheets cannot convey. Direct tensile tests characterize the reinforcement itself, but once a composite is glued to a cementitious substrate, performance emerges from the interplay of matrix cracking, adhesive stress transfer, woven geometry, and the governing failure mechanism. The configuration that wins in tension lost in bending; the one that ruled bending fared poorly in compression. The authors therefore recommend matching the fabric to the demand: diagonal carbon-glass for flexure-dominated members, carbon-glass vertical or glass-aramid horizontal for compression-dominated ones, with carbon-glass vertical the most balanced choice overall—and vertical glass-aramid layouts to be avoided. They also caution that these are laboratory-scale results from homogeneous mortar, with bond behavior, environmental durability, cyclic seismic loading, and full-scale masonry geometry still to be verified. For the aging bridges, walls, and heritage structures that increasingly need help carrying their load, the study offers a deceptively simple design rule: orient the strongest direction of the fabric along the principal tensile stress, whether that runs down a beam or around a column, and let the weave do the rest.

Subject of Research: Structural strengthening of mortar elements using intraply hybrid composite fabrics with varied fiber combinations and reinforcement orientations

Article Title: Structural performance of mortar elements strengthened with intraply hybrid composite fabrics: Combined effects of fiber hybridization and reinforcement orientation

Article References: Cakir, F., Yildirim, P., & Shams, M. (2026). Structural performance of mortar elements strengthened with intraply hybrid composite fabrics: Combined effects of fiber hybridization and reinforcement orientation. Case Studies in Construction Materials, 25, Article e06610. https://doi.org/10.1016/j.cscm.2026.e06610

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06610

Keywords: hybrid composites, fiber-reinforced polymer, mortar strengthening, flexural strength, confinement, carbon fiber, glass fiber, aramid fiber, fiber orientation, structural rehabilitation, masonry, textile reinforcement

The research team, led by Luthfi and colleagues, fabricated composites containing five different volume fractions of sago pith waste, from 20 to 40 percent, in a commercial orthophthalic unsaturated polyester resin identified as SHCP 3315, cured with 1.5 weight percent methyl ethyl ketone peroxide hardener. Before any mixing began, the raw waste collected from facilities in Lhokseumawe had to be cleaned. The material was washed repeatedly in plain water, stirred and squeezed to strip away residual soil and sand, then sun-dried for five to seven days. Moisture content was verified with a gravimetric oven method at 60 degrees Celsius, and only batches drying below 2 percent moisture were accepted. During drying, the pith gradually shifted from white to light brown, a visual signature of moisture loss and natural oxidation.

Because dried sago pith tends to clump into soft agglomerates that could seed weak spots in a finished panel, the team sieved the material through a 20-mesh screen, capping particle size at roughly 0.841 millimeters. Notably, they skipped the glycerol plasticization used in earlier sago-waste studies, deliberately choosing a simpler and cheaper route. The apparent density of the sieved particles was estimated at 1.4286 grams per cubic centimeter using a simple ethanol displacement calculation, a value the authors candidly flag as an estimate rather than a validated true density, since no calibrated pycnometer or degassing was employed. That honesty matters, because the same number feeds into the theoretical density and porosity calculations that frame the entire mechanical analysis.

The composites themselves were mixed by hand, homogenized with a motorized mixer, and cast into 300 by 300 by 10 millimeter molds lined with aluminum foil, curing at room temperature for at least 24 hours. Three formulations, at 20, 30, and 40 percent sago pith waste, served most physical and thermal tests, while intermediate compositions at 25 and 35 percent were fabricated specifically to sharpen the mechanical trend analysis. Density measurements told the first part of the story: experimental density fell steadily from 1.08435 grams per cubic centimeter at 20 percent filler to 1.00232 at 40 percent, while estimated porosity climbed from 8.86 percent to 19.78 percent. In other words, more sago means a lighter panel, but also one riddled with more internal voids, as the resin increasingly struggles to wet and penetrate the growing mass of particles.

Flexural performance followed the same downward slope. In modified three-point bending tests on 200 by 15 by 10 millimeter specimens over a 160 millimeter span, average bending strength dropped from 3.87 kilograms-force per square millimeter for the 20 percent composite to 2.92 for the 40 percent version, and the maximum bending moment fell from 1.611 to 1.219 kilograms-force meters. A one-way analysis of variance confirmed these differences were statistically significant, with F values of 20.68 for moment and 19.06 for stress and p-values in the millionths. Strain at failure, intriguingly, showed a rising trend with more filler, from 1.19 to 1.35 percent, but the ANOVA returned p equal to 0.265, so the authors correctly decline to claim that sago content meaningfully changes how far the material bends before it breaks.

Scanning electron microscopy of the fractured surfaces explains why the strength falls. Micrographs of the 20 percent composite revealed residual sago starch granules roughly 20 to 30 micrometers across, cracked polyester matrix, and irregular voids with torn edges. Clean particle pull-out and interfacial gaps pointed to weak adhesion between the untreated lignocellulosic filler and the resin, meaning stress is not transferred efficiently across the interface. To separate failure damage from manufacturing defects, the team also imaged carefully cut, unfractured cross-sections, where voids appeared smoother and near-spherical, the classic fingerprint of air bubbles entrapped during mixing and molding. The 40 percent composite showed all of these features in greater abundance, consistent with its highest porosity, and the authors conclude that interfacial optimization, such as surface treatment of the particles, is the clearest path to better performance.

Fourier transform infrared spectroscopy added the chemical dimension. Using potassium bromide pellets, the team found all composites dominated by the polyester’s ester carbonyl stretch near 1730 inverse centimeters, with a broad hydroxyl band around 3533 to 3539 inverse centimeters growing more pronounced as sago content rose, reflecting the cellulose, hemicellulose, and absorbed water carried in with the biomass. Crucially, no new absorption bands unique to the composites appeared, indicating that sago pith and polyester interact primarily through physical rather than covalent chemical bonding. That chemical aloofness at the interface dovetails neatly with the pull-out features seen under the electron microscope.

Thermal analysis rounded out the picture. Differential scanning calorimetry showed the glass transition temperature sliding from 58 degrees Celsius at 20 percent sago to 54 at 30 percent and 50 at 40 percent, a shift the authors attribute to changes in crosslink density, interfacial region volume, and free volume when bio-filler particles enter the network. Because cured unsaturated polyester is a crosslinked thermoset, the broad high-temperature endotherms, which shifted from 165 to 200 degrees Celsius and grew in enthalpy from 3.74 to 5.86 joules per gram, reflect relaxation and thermally activated transitions rather than any true melting. Thermogravimetric analysis under nitrogen revealed multi-stage degradation: negligible moisture loss below 150 degrees Celsius, a 4 to 6 percent stage linked to hemicellulose decomposition up to 330 degrees, and a massive degradation stage between 331 and 490 degrees where more than 80 percent of the mass vanished. Final residues at 600 degrees Celsius ranged from 6.57 to 7.44 percent, with the 40 percent composite retaining the most, likely carbonaceous char from lignin plus natural mineral ash, though the authors caution the trend is not systematic.

Taken together, the study delivers a sober but genuinely useful verdict: sago pith waste can indeed be incorporated into unsaturated polyester as a renewable, nearly free filler, lightening the material while leaving the resin’s chemistry intact, but rising filler content drags in porosity and interfacial defects that erode bending strength. The authors frame the work as the integrating chapter of a broader program that previously examined tensile, acoustic, and thermal-conductivity behavior separately, and they point squarely at future work on particle-size optimization, improved processing, and surface chemical modification of the waste as the levers that could turn an agricultural liability into panels for insulation, construction, and other value-added uses. For Indonesia’s sago mills, the residue currently rotting behind the factory may be one sieve, one mixer, and one better interface away from a second life.

Subject of Research: Characterization of sago pith waste-filled unsaturated polyester composites

Article Title: The analysis of sago pith waste – unsaturated polyester composites by mechanical, SEM, FTIR, DSC, and TGA tests

Article References: Luthfi, Azhar, Jagodang, H., Riyadhsyah, T., Rihayat, T., & Setiawan, A. (2026). The analysis of sago pith waste – unsaturated polyester composites by mechanical, SEM, FTIR, DSC, and TGA tests. Environmental Challenges, 25, Article 101681. https://doi.org/10.1016/j.envc.2026.101681

Image Credits: AI Generated

DOI: 10.1016/j.envc.2026.101681

Keywords: sago pith waste, unsaturated polyester resin, natural fiber composites, flexural strength, porosity, FTIR, DSC, TGA, SEM, biomass waste utilization, Indonesia, thermal degradation

The new materials belong to a class known as mycelium biocomposites, in which the vegetative root-like networks of fungi are grown through organic substrates such as agricultural residues. The fungal hyphae bind the loose lignocellulosic particles into a solid, relatively lightweight structure that is biodegradable and recyclable. Historically an experimental biomaterial, mycelium composites have attracted growing attention because of their promising combination of low weight, thermal insulation capacity, and reasonable strength and durability. Their production also offers a route to valorizing by-products, storing atmospheric carbon dioxide, and reducing dependence on petrochemicals, all while embodying circular economy principles in which materials can be disassembled, reused, and ultimately returned to natural systems.

Producing these composites is a multi-phase biological process rather than an industrial extrusion. Mycelium is first grown on a substrate over one to two weeks under carefully controlled conditions, typically at temperatures between 24 and 30 degrees Celsius and humidity levels of 60 to 75 percent. The material then develops for two to four weeks as the fungal network colonizes the substrate into a uniformly dense structure. A final drying stage, lasting from a few days to a week, halts fungal growth and provides the strength and dimensional stability that make the material usable in construction. Each of these steps, along with the choice of substrate and fungal strain, shapes the physicochemical characteristics of the finished composite.

In the new study, a research team prepared four experimental series of mycelium biocomposites, each with a different composition, production flow, and specimen geometry. Series I combined wheat straw with Ganoderma lucidum, Series II paired flax straw with Pleurotus ostreatus, Series III used hemp shives with Pleurotus ostreatus, and Series IV tested wheat straw, hemp shives, and flax straw, each inoculated with Ganoderma lucidum. All samples were produced by mixing 7.5 grams of colonized grain spawn into 300 grams of sterilized straw, a spawn-to-substrate ratio of 2.5 percent, with the sterilized substrate held at approximately 60 percent preparative moisture. The mixtures were compressed by hand into cardboard molds shaped as cubes, cylinders, or rectangular prisms, then cultivated and dried under formulation-specific conditions before testing.

The team evaluated four parameters most relevant to insulation performance: thermal conductivity, density, flexural strength, and compressive strength. Density was measured with a precision laboratory balance and manual dimensional measurements, while thermal conductivity was assessed with a portable Isomet 2114 heat transfer analyzer under controlled laboratory conditions of 20 degrees Celsius and 50 percent relative humidity. Each specimen was measured twice on adjacent surfaces, with the median value used for analysis. The researchers also computed a thermal conductivity-to-weight ratio, an inverse indicator that favors formulations combining low heat conduction with low bulk density, to compare the overall thermal-mass balance of the tested materials.

The results revealed striking differences among the formulations. Thermal conductivity ranged from 0.0385 to 0.0719 watts per meter-kelvin depending on substrate and fungal strain, while densities spanned from 80 to 227 kilograms per cubic meter. The standout performer was the hemp shive composite inoculated with Pleurotus ostreatus, which achieved the lowest density range of 80 to 120 kilograms per cubic meter and the most efficient thermal conductivity, from 0.0385 to 0.057 watts per meter-kelvin. This formulation recorded the highest thermal conductivity-to-weight ratio of 0.209, approximately 35.7 percent higher than the next best formulation in the study. By contrast, the multi-material Series IV showed the widest variability in both density and conductivity, reflecting the challenges of consistency in mixed compositions.

Mechanical testing of the optimal hemp shive and Pleurotus ostreatus composite produced equally notable results. Two independently molded prism specimens, each 40 by 40 by 160 millimeters, were subjected to three-point bending on a standardized flexure testing device with a 100-millimeter support span. The composite achieved an average flexural strength of 8.85 megapascals, with individual specimens reaching 8.58 and 9.11 megapascals. Compressive testing on the uncracked halves of the broken prisms yielded an average compressive strength of 4.25 megapascals. Both values exceed or match similar mycelium-based composites described in the literature, where flexural strengths have typically ranged from 0.44 to 4.23 megapascals depending on substrate, and many lignocellulosic formulations have shown compressive strengths below 1 megapascal.

To contextualize these findings, the researchers benchmarked their data against seven published studies of mycelium composites made from comparable plant-derived substrates, plotting thermal conductivity jointly with density because porosity and density strongly influence thermal performance. The literature dataset spans roughly 0.035 to 0.096 watts per meter-kelvin across a wide density range. The hemp shive composite’s minimum conductivity of 0.0385 watts per meter-kelvin compares favorably with values reported for birch sawdust composites and mycelium-bound fibers from invasive plants, and its combination of approximately 100 kilograms per cubic meter density with low conductivity places it firmly in the favorable low-density, low-conductivity region of the performance map. The authors caution, however, that differences in specimen geometry, moisture state, processing conditions, and measurement procedures mean such comparisons serve as performance benchmarking rather than a strictly standardized ranking.

The researchers supplemented their measurements with scanning electron microscopy of the wheat straw and Ganoderma lucidum formulation, which revealed an interconnected filamentous network bridging the lignocellulosic structural elements and numerous micrometer-scale voids. These images provide qualitative evidence of the porous microstructure that underpins the materials’ insulating behavior, although porosity was not quantitatively determined. The team also conducted a rigorous uncertainty analysis, estimating measurement-related uncertainties of roughly 0.6 to 1.3 percent for density, 6.4 to 7.6 percent for thermal conductivity, 3.0 percent for flexural strength, and 2.0 percent for compressive strength, ensuring the reported values rest on a transparent methodological foundation.

The implications extend beyond the laboratory. The hemp shive and Pleurotus ostreatus composite appears suitable for non-load-bearing panels, partition walls, insulation boards, and lightweight structural components, applications where its combination of insulation efficiency, mechanical cohesion, and biodegradability offers genuine advantages over conventional materials. The authors emphasize that their mechanical values rest on limited replication and that future work must address scalability, fire behavior, moisture resistance, biological durability, ageing, dimensional stability, and industrial-scale manufacturability before building-scale deployment. Nevertheless, the study provides practical guidance for future research, industrial pilot projects, and policy-driven adoption of eco-composites. As the construction sector confronts its outsized carbon footprint, materials grown from fungal networks and farm waste are moving from curiosity toward credible contender, proving that the walls of future buildings might one day be cultivated in a matter of weeks.

Subject of Research: Thermal and mechanical performance of mycelium-agricultural waste biocomposites for building insulation

Article Title: Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance

Article References: Babenko, M., Kononets, Y., Kunes, R., Makys, P., Spalek, F., Sramhauser, K., Hanzal, P., Majernik, J., Zoubek, T., & Bartos, P. (2026). Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance. Cleaner Engineering and Technology, Article 101334. https://doi.org/10.1016/j.clet.2026.101334

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101334

Keywords: mycelium biocomposites, building insulation, hemp shives, Pleurotus ostreatus, Ganoderma lucidum, thermal conductivity, agricultural waste, sustainable construction, circular economy, flexural strength, compressive strength, lignocellulosic substrates

LECA is a manufactured aggregate produced by expanding clay at high temperature, yielding hard, spherical granules riddled with internal voids. Because it weighs far less than natural sand and gravel, it is attractive for lightweight concrete, which reduces structural dead load and improves thermal and acoustic insulation while lowering cost. The catch is well documented: previous studies found that replacing natural aggregate with LECA can significantly weaken concrete. Corinaldesi and Moriconi reported compressive strength losses of roughly 18 to 28 percent when natural sand was replaced with LECA in self-compacting concrete, and Youm and colleagues found that coarse LECA reduced splitting tensile strength, compressive strength, and elastic modulus by up to nearly 48 percent. Polypropylene fibers, meanwhile, are known to stitch microcracks together and improve toughness, but above roughly 0.3 percent by weight of cement they tend to clump and ball during mixing, degrading the mix rather than improving it.

The Iranian research team set out to explore the underexplored middle ground: what happens when a modest 10 percent of sand is replaced by volume with LECA and a modest 0.2 percent by volume of polypropylene fibers is added, individually and in combination? They prepared four mortar mixes with a constant cement content of 670 kilograms per cubic meter and a water content of 302 kilograms per cubic meter: a plain control mix (P0L0), a mix with 10 percent LECA (P0L10), a mix with 0.2 percent fibers (P0.2L0), and a hybrid containing both (P0.2L10). The LECA had dry and saturated surface-dry densities of 1542 and 1704 kilograms per cubic meter with 5.0 percent water absorption, while the fibers were 12 millimeters long, 19 micrometers in diameter, with a tensile strength of 400 megapascals. Fibers were added gradually in several steps to ensure uniform dispersion, and cube and prismatic specimens were water-cured and tested at 3, 7, 14, and 28 days.

The compressive strength results reveal a striking early-age reversal. Replacing sand with LECA alone cut the 3-day strength from 19.20 to 15.87 megapascals, a drop of about 17.4 percent, as expected from the porous, weaker aggregate. Yet by 14 and 28 days the LECA mix had overtaken the control, with gains of 23.8 and 18.2 percent respectively. The authors attribute this to LECA’s internal water reservoir effect: the porous aggregate absorbs mixing water early and gradually releases it during hydration, densifying the cement matrix and strengthening the bond between paste and aggregate over time. Fibers alone had little effect at 3 days but raised 7-day strength by about 26.9 percent, from 24.27 to 30.80 megapascals, by bridging and restraining early microcracks during setting.

The hybrid mix delivered the best of both worlds early on. Combining LECA and fibers lifted 3-day compressive strength by roughly 23 percent, to 23.60 megapascals, and 7-day strength by about 25 percent, to 30.27 megapascals, compared with the control. At 28 days, however, the benefit largely evaporated: the hybrid reached only 32.80 megapascals, a marginal 2 percent gain over the control and slightly below the LECA-only mix. The researchers explain that by later ages the fiber-induced voids and weak fiber–matrix interfaces begin to offset LECA’s hydration benefits. Interestingly, the standard logarithmic strength-versus-time model fit the fiber-containing mixes poorly, with a bi-linear relationship describing their development better.

Flexural strength told an even more compelling story. LECA alone reduced early flexural strength, dropping the 3-day value from 6.43 to 4.70 megapascals and the 7-day value by about 16.5 percent, because its porous structure weakens the aggregate–paste interface. Fibers alone slightly hurt 3-day flexural strength but boosted it substantially from 7 to 28 days, reaching 11.69 megapascals at 28 days, thanks to their crack-bridging action under bending stresses. The hybrid mix, however, produced the highest flexural strength at every single age tested: 6.74, 7.95, 9.12, and 10.75 megapascals at 3, 7, 14, and 28 days respectively. Continued hydration refined the matrix while the fibers delayed crack propagation, a synergy that proved most valuable precisely where concrete is most vulnerable—under tension at early ages.

Durability was probed with two complementary techniques. In the Rapid Chloride Migration Test, performed according to AASHTO TP64 on 28-day cylinders, a 60-volt direct field drives chloride ions from a sodium chloride solution into the specimen for about 18 hours, after which silver nitrate spraying reveals the penetration depth. The control mix showed a migration rate of 0.0123 millimeters per volt-hour. Adding 10 percent LECA reduced this by about 4.9 percent to 0.0117, an improvement the authors link to increased tortuosity of transport pathways. Fibers alone left migration essentially unchanged, and the hybrid mix measured 0.0125, only marginally above the control. Electrical conductivity, measured with an alternating-current system to avoid polarization errors, dropped noticeably in the LECA mixes, from 0.0370 to 0.0339 per ohm-meter, confirming that the lightweight aggregate interrupts the continuous capillary pore network that normally serves as the highway for ion movement.

Scanning electron microscopy helped explain why apparent porosity and actual transport do not always go hand in hand. Images of LECA-containing specimens revealed abundant spherical voids up to 188 micrometers across, and in the hybrid mix up to 395 micrometers, yet these belong largely to the sealed interior of the LECA particles themselves, whose impervious outer shell and dense interfacial transition zone keep them out of the connected pore network. Fluid and ion transport occurs mainly through the fine capillary pores of the cement paste, and LECA particles interrupt that network, forcing ions onto longer, more winding paths. The microscopy also exposed a subtle trade-off with the fibers: hydrophobic polypropylene bonds poorly to the hydrophilic cement matrix, creating micro-gaps of roughly 15 to 30 micrometers around the filaments and at the LECA interface. These gaps do not connect into continuous channels, but under the sustained 60-volt field of the migration test they can act as local weak zones, which is why the hybrid mix showed slightly higher chloride migration despite lower overall conductivity.

The broader significance lies in the balance achieved. Previous studies in which large amounts of lightweight aggregate weakened the matrix, or in which high fiber dosages caused clustering and non-uniform transport, suggest that more is not better. By capping LECA at 10 percent sand replacement and fibers at 0.2 percent by volume, the researchers produced a composite that reaches 32.80 megapascals in compression and 10.75 megapascals in flexure at 28 days, resists bulk ion transport by disrupting continuous capillary pathways, and weighs measurably less than the control, at 2.03 versus 1.92 grams per cubic centimeter for the LECA mixes. For infrastructure exposed to chlorides—marine structures, bridge decks, and pavements subjected to de-icing salts—such a material could extend service life while reducing structural weight. The study also delivers a methodological caution: mechanical strength alone does not capture durability, and pairing migration testing with conductivity measurements, as this team did, reveals transport behavior that strength data alone would hide. As lightweight and fiber-reinforced concretes move toward wider structural use, this kind of coupled mechanical–transport–microstructural framework may become the standard by which new mixes are judged.

Subject of Research: Mechanical and durability characterization of polypropylene fiber-reinforced mortar containing lightweight expanded clay aggregate

Article Title: RCMT, electrical conductivity, and mechanical characterization of polypropylene fiber-reinforced LECA mortar

Article References: Taghvaei, D., Behzad, P., Ghaderan, S., & Dastan Diznab, M. A. (2026). RCMT, electrical conductivity, and mechanical characterization of polypropylene fiber-reinforced LECA mortar. Results in Engineering, 32, Article 113256. https://doi.org/10.1016/j.rineng.2026.113256

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113256

Keywords: LECA, polypropylene fibers, lightweight concrete, chloride migration, electrical conductivity, compressive strength, flexural strength, durability, pore structure, SEM, cement mortar, RCMT

The concept borrows from a classic of aerospace engineering: the sandwich composite. Two stiff outer skins are bonded to a lightweight core, and under bending the skins carry most of the tensile and compressive stress while the core resists shear and crushing. By holding the skins apart, the core dramatically increases the panel’s moment of inertia, meaning it resists bending far better than its weight would suggest. Honeycomb and foam cores have long served aircraft and ships, but the Brazilian team wanted a core that grows in a few years, sequesters carbon as it grows, and would otherwise be thrown away.

Bamboo fits that brief almost perfectly. The researchers worked with Phyllostachys aurea, a species harvested at the University of São Paulo’s Pirassununga campus, using the lower portions of roughly three-year-old culms. The waste problem they aimed to address is striking: bamboo shoot processing discards about 70 percent of the harvested material, and conventional culm harvesting leaves behind branches, leaves, and upper sections that account for a significant share of aboveground biomass. Upcycling this residue into engineered structural components could turn a disposal burden into a carbon-storing asset, since bamboo construction materials have been shown to yield lower life-cycle emissions than steel, concrete, and even some novel low-carbon cements.

Preparing the rings involved a preservation step borrowed from established bamboo engineering practice. The culms were immersed for seven days in an 8 percent aqueous solution of disodium octaborate tetrahedrate, a borate treatment that protects the lignocellulosic material against biological attack, then air-dried for another week. The natural circular cross-section of the culm was retained, producing rings about 30.5 millimeters in outer diameter with a mean wall thickness of 4.4 millimeters. That diameter was not arbitrary: earlier studies found 30-millimeter rings outperform both smaller 20-millimeter rings and larger 45-millimeter rings in flexural strength and stiffness, making them the sweet spot for sandwich cores.

The facings were commercial fiber cement boards with a bulk density of 1.28 grams per cubic centimeter, a flexural strength of 6.80 megapascals, and an elastic modulus of 2.44 gigapascals. Spectroscopic and mineralogical analysis using Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction revealed a carbonated cementitious matrix containing portlandite, calcite, quartz, and residual alite. The bonding agent was a two-component polyurethane adhesive derived from castor oil, a bio-based resin with a 24-hour cure time that has become a favorite in sustainable composites research because it replaces petroleum-derived alternatives.

The experimental design was a rigorous full-factorial program. The team built 32 panels across eight configurations, varying three factors at two levels each: core height of 20 or 30 millimeters, compact versus gapped hexagonal ring arrangement, and adhesive bond-line thickness of 0.75 or 1.00 millimeters. Compact cores packed 23 rings tightly, leaving about 61 percent of the panel plan area as void, while gapped cores used 19 rings and pushed the void fraction to 73 percent. Panels were assembled under a gentle cold pressure of 2.3 kilopascals and tested in three-point bending according to the ASTM C393 standard, alongside measurements of density, thermal conductivity, and sound pressure levels.

The results delivered a genuinely counterintuitive lesson in structural mechanics. Making the core taller, from 20 to 30 millimeters, cut the equivalent density by 16.2 percent and boosted flexural rigidity by 86 percent in compact panels and 109 percent in gapped ones, exactly as sandwich theory predicts when skins move further from the neutral axis. Yet the taller panels were weaker in apparent flexural strength, dropping by 22 percent in compact and a dramatic 48 percent in gapped configurations. The gapped 30-millimeter panels also suffered a 33 percent reduction in nominal core shear stress, a consequence of fewer rings, smaller contact area between core and facing, reduced core continuity, and differences in specimen geometry. Lighter, it turns out, is not automatically better.

The standout performer was the 20-millimeter gapped panel with the thinner 0.75-millimeter adhesive line, which achieved the highest specific strength of 8.80 megapascal-centimeters-cubed per gram and the highest specific modulus among all configurations. Its low density more than compensated for a modest loss in absolute strength. Notably, thinning the adhesive line cut resin consumption by about 25 percent without significantly affecting flexural strength, and the adhesive content of 5.9 to 9.3 percent of panel mass compared favorably with bamboo boards that typically demand 10 to 20 percent resin. Failure analysis through microscopy showed that most panels failed by tensile cracking of the lower fiber cement facing, a sign that the adhesive bonds held firm, while the bamboo rings themselves never crushed under the loading nose, thanks to their impressive 64-megapascal compressive strength and 6-gigapascal modulus.

The thermal and acoustic results add practical appeal. Estimated thermal conductivity came in at 0.276 watts per meter-kelvin for compact panels and 0.260 for gapped ones, an order of magnitude below the 1.6 to 3.2 range typical of normal-weight concrete, thanks to the insulating air cavities threaded through the core. Acoustic testing at 125, 500, 1000, and 2000 hertz showed frequency-dependent sound pressure reductions, with significant differences between compact and gapped panels at 125 and 1000 hertz, likely reflecting internal scattering and viscous dissipation within the bamboo’s porous cellular architecture. The authors caution that these were comparative laboratory estimates rather than standardized absorption or transmission-loss measurements.

The researchers are candid about the road ahead before bamboo-ring panels reach real buildings. Future work must address concentrated-load resistance, screw-holding capacity, impact behavior, long-term durability under moisture and weathering, fire response, and full-scale wall-system testing. Still, the study demonstrates that a material once destined for the compost heap can be engineered into a panel that is lighter than conventional cementitious alternatives, thermally insulating, acoustically functional, and mechanically competitive, all while locking away biogenic carbon. As the construction industry scrambles to decarbonize, the answer may lie in a field of bamboo, sliced into rings and glued together with castor oil.

Subject of Research: Lightweight bamboo-ring core sandwich panels with fiber cement facings for sustainable construction

Article Title: Lightweight sandwich panels with bamboo-ring cores and fiber cement facings

Article References: Emadifard, A., Azevedo, A., Fioroni, C., Gholizadeh, P., Batista, F., Panzera, T., & Savastano, H., Jr. (2026). Lightweight sandwich panels with bamboo-ring cores and fiber cement facings. Results in Engineering, 32, Article 113327. https://doi.org/10.1016/j.rineng.2026.113327

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113327

Keywords: bamboo, sandwich panels, fiber cement, polyurethane adhesive, flexural strength, thermal conductivity, acoustics, sustainable construction, Phyllostachys aurea, core geometry, carbon emissions, building materials

The central challenge the researchers set out to solve is a familiar one in composite design: no single reinforcement does everything well. Basalt fiber, made by melting and drawing out volcanic basalt rock, offers excellent stiffness, good chemical and thermal resistance, and a far smaller environmental footprint than glass fiber, since it requires no exotic chemical feedstocks. Ultra-high molecular weight polyethylene, or UHMWPE, brings extraordinary toughness, low density, and outstanding impact and abrasion resistance, but it is soft and contributes little to bending stiffness. When the team fabricated laminates reinforced exclusively with basalt fiber, they observed a decline in flexural strength; when they used only UHMWPE fiber, tensile strength dropped. Both problems were traced to fabrication difficulties at higher fiber contents, where the hand layup process struggles to wet out and consolidate dense fiber beds, leaving voids and weak interfaces that crack under load.

The solution was hybridization. Rather than betting on one fiber, the researchers built laminates that combined basalt fiber, UHMWPE fiber, and an epoxy matrix in varying weight proportions, systematically varying the UHMWPE content from 5 to 15 percent by weight. Hand layup, the simplest and most accessible composite manufacturing method, was used throughout, which matters because it means the process could be transferred to workshops without expensive autoclaves or automated fiber placement equipment. Each laminate was then cut and tested according to ASTM standards for tensile strength, flexural strength, interlaminar shear strength, hardness, and density, with dynamic mechanical analysis used to probe how stiffness and damping evolve with temperature.

The sweet spot emerged at a laminate the team designated LD, containing 45 percent basalt fiber, 10 percent UHMWPE fiber, and 45 percent epoxy. This composition showed significant enhancements in both tensile and flexural properties compared with the single-fiber laminates. The mechanics behind the improvement are instructive. The stiff basalt fibers carry the bulk of the tensile and bending loads, while the ductile UHMWPE fibers bridge cracks, absorb impact energy, and blunt stress concentrations at the fiber-matrix interface. Because neither fiber dominates the architecture, the wetting problems that plagued the high-fiber-content single-fiber laminates are avoided, and the load transfer between phases becomes more efficient. It is a textbook demonstration of the hybridization principle: combining reinforcements with complementary properties to escape the trade-offs that constrain each one alone.

But the team did not stop there. Interlaminar shear strength, the property that governs how well the layers of a laminate resist sliding apart, is often the Achilles heel of hand-laid composites, and delamination is the failure mode that most often ends a structural panel’s service life. To attack it, the researchers incorporated natural garnet powder as a particulate filler at loadings of 2 to 5 percent by weight into the LD laminate formulation. Garnet is a hard, dense silicate mineral, and when its fine particles disperse through the epoxy matrix they stiffen the resin between fiber layers, roughen the fracture surfaces so cracks must follow more tortuous paths, and improve the microstructure of the cured composite. The filler also plays a role in damping, dissipating vibrational energy through friction at particle-matrix interfaces.

The optimized laminate, designated LK2, contains 45 percent basalt fiber, 10 percent UHMWPE fiber, 3 percent garnet filler, and 42 percent epoxy. That modest 3 percent garnet loading proved optimal: enough to reinforce the matrix and interlock the layers, but not so much that the particles agglomerate and become defect sites. The measured performance is impressive for a hand-laid-up material. Tensile strength reached 406.4 megapascals, flexural strength 603.25 megapascals, and interlaminar shear strength 17.01 megapascals, alongside enhanced damping properties and an improved microstructure confirmed by microscopic examination of the fracture surfaces.

Perhaps the most consequential results come from the dynamic mechanical analysis, which evaluated the laminates across a temperature range of 25 to 140 degrees Celsius. In this window, the LK2 laminate maintained a balanced combination of strength, stiffness, and damping capability. That temperature span covers the operating conditions of most automotive and transportation interiors, where panels must remain stiff on a hot summer dashboard yet still absorb vibration and noise. Damping is a property that structural engineers often sacrifice for stiffness, since stiff, highly cross-linked systems tend to ring like bells. A laminate that offers both, in a low-density package, addresses a persistent tension in lightweight design, where adding damping layers usually means adding weight.

The choice of ingredients also carries a sustainability story. Basalt fiber is produced from abundant volcanic rock with a single-step melt-spinning process, avoiding the energy-intensive chemistry of glass fiber production and the cost of carbon fiber. Garnet is a natural mineral, and UHMWPE, while a synthetic polymer, is chemically inert and extremely durable. None of the constituents require rare or critical raw materials, and the hand layup process itself consumes little energy. For industries under pressure to lightweight vehicles and structures without multiplying their embodied carbon, a composite built from rock, plastic, and sand-grade mineral has obvious appeal, even if the study did not include a formal life-cycle assessment.

The authors are careful about scope. The work characterizes laboratory-scale laminates under quasi-static and dynamic mechanical loading; it does not report long-term fatigue data, impact testing, weathering, or flame performance, all of which would be needed before certification in transport applications. The researchers also note that no datasets were generated or analysed during the study beyond those in the paper, and that the research received no specific grant from funding agencies. Still, the property set they document, combining strength, stiffness, interlaminar toughness, and damping over a practical temperature range, maps directly onto the wish lists of designers of lightweight structural panels, vehicle interiors, machine housings, and protective covers.

What makes the study broadly interesting is its demonstration that sophisticated composite performance does not require exotic chemistry or billion-dollar manufacturing lines. By tuning the proportions of two very different fibers, a stiff mineral fiber and a tough polymer fiber, and then adding a few weight percent of a common natural mineral to glue the architecture together at the microscale, the team achieved a material whose numbers rival those of more expensive systems while remaining manufacturable in a basic workshop. As the search for affordable, lower-impact structural materials intensifies across the automotive and industrial sectors, hybrid laminates like LK2 suggest that sometimes the answer lies not in inventing new substances, but in recombining old ones in just the right proportions.

Subject of Research: Mechanical and dynamic characterization of hybrid UHMWPE/basalt epoxy composites reinforced with garnet filler

Article Title: Mechanical and dynamic behavior of UHMWPE/Basalt hybrid polymer-matrix composites with garnet filler reinforcement for structural applications

Article References: Raghavendra Rao, R., Sharath, B. N., Madhu, P., Pradeep, D. G., & Pradeep, S. (2026). Mechanical and dynamic behavior of UHMWPE/Basalt hybrid polymer-matrix composites with garnet filler reinforcement for structural applications. Polymer Bulletin, 83(12), Article 672. https://doi.org/10.1007/s00289-026-06734-6

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06734-6

Keywords: UHMWPE, basalt fiber, garnet filler, hybrid polymer composites, epoxy matrix, hand layup, tensile strength, flexural strength, interlaminar shear strength, damping, dynamic mechanical analysis, lightweight structures

The material at the center of the research is the thin spray-on liner, or TSL, a flexible support layer sprayed onto rock surfaces in layers typically 5 to 20 millimeters thick. Unlike rigid shotcrete, a well-designed TSL penetrates micro-fractures in the rock during application, binds fragmented rock into a continuous load-bearing composite, and forms a shallow load-bearing arch in partnership with the surrounding ground. Commercial TSLs fall into two families: latex-based products, which are highly ductile but prohibitively expensive, and polymer-modified cementitious liners, which are cost-effective but historically too stiff and brittle for the demands of deep tunnels with large deformation. The research team, led by Xing Gao and Jinlong Teng, set out to close that performance gap with fiber reinforcement.

The researchers formulated a two-component cementitious TSL from white cement, fine quartz sand, vinyl acetate-ethylene copolymer powder, and various admixtures, then added chopped glass fibers at four dosage levels: 0, 0.5, 1.0, and 1.5 percent of the powder mass. The fibers themselves were slender, 6-millimeter strands with a tensile strength of 555 megapascals and an aspect ratio of nearly 484. Specimens were cast, cured for seven days under controlled temperature and humidity, and then subjected to uniaxial compression and three-point bending tests, each group run with six parallel samples to ensure statistical reliability.

What distinguishes this study from earlier work is its insistence on measuring toughness across the entire loading-to-failure process, not just at the peak. Using an energy-based framework rooted in the first law of thermodynamics, the team partitioned the compressive response of each specimen into four stages: compaction, elastic deformation, stable crack expansion, and post-peak accelerated crack growth. By integrating the stress-strain curves, they separated the total input energy into stored elastic energy and dissipated energy, the latter consumed by crack closure, crack propagation, and frictional sliding on fracture surfaces. From this accounting they derived a pre-peak toughness index, a post-peak toughness index normalized against the unreinforced material, and a coupled comprehensive compressive toughness index formed by their product.

The results traced a clear arc of improvement followed by decline. Compressive strength rose from 12.64 megapascals in the unreinforced liner to a peak of 14.75 megapascals at 1 percent fiber content, then fell back to 12.85 megapascals at 1.5 percent. Energy absorption followed the same pattern, peaking at 317.9 kilojoules per cubic meter at the 1 percent dosage. Failure modes evolved in parallel: the unreinforced material split with two longitudinal tensile cracks and shed fragments, the 0.5 percent mix developed a combined tension-shear crack pattern, the 1 percent mix failed through a single diagonal shear band while remaining intact, and the 1.5 percent mix displayed a complex tri-directional shear crack network with pronounced ductile dilation. The comprehensive compressive toughness index nearly doubled, climbing from about 0.48 to 0.93 across the fiber range.

Flexural testing told an equally striking story. Flexural strength peaked at 8.47 megapascals at 1 percent fiber content, a 77.2 percent gain over the unreinforced matrix, while fracture energy surged more than fivefold, from 408.53 newtons per meter to 2189.69 newtons per meter at the highest fiber dosage. The flexural toughness ratio climbed steadily from 0.22 to nearly 0.68. Crack lengths in bending shrank progressively from 37.5 millimeters in the unreinforced beams to 27 millimeters in the most heavily reinforced ones, and the post-peak load response shifted from a cliff-like brittle drop to a gentle stress-tailing curve sustained by the dense fiber network bridging the main crack.

To unify these findings, the team constructed a comprehensive toughness index R that multiplies the pre-peak compressive index, the post-peak compressive index, and the flexural toughness ratio. The multiplicative, non-compensatory design ensures that weakness in any single dimension drags down the overall score. The index rose from roughly 0.10 to 0.63 as fiber content increased, and unlike the flexural-to-compressive strength ratio, which peaked at 1 percent and then declined, R kept rising because it captured the continuously improving post-peak energy dissipation. Independent validation against failure modes and crack patterns confirmed that R tracked actual toughness evolution more faithfully than strength-based measures alone.

Beneath the macroscopic numbers lies a more complicated microscopic story, one the authors describe as a competition between positive toughening and negative damage. Microscopy of fracture surfaces and helium pycnometry revealed that fibers hinder the migration and escape of air bubbles during mixing and compaction, a cofferdam effect that traps pores near fiber intersections and, at high dosages, produces fiber agglomeration and continuous defect zones. Porosity fluctuated in a rise-fall-rise pattern, reaching its lowest value of 10.54 percent at the 1 percent dosage, where the fiber network achieved its optimal spatial arrangement. This pore evolution explained the ladder-like drop in elastic modulus and the sharper strength penalty under bending, which is far more defect-sensitive than compression: flexural strength fell 25.9 percent at 1.5 percent fiber content, against only 13.2 percent for compressive strength.

Field-emission scanning electron microscopy exposed the three-stage energy dissipation mechanism that gives the material its resilience. First, hydration products, including calcium silicate hydrate gel, calcium hydroxide platelets, and polymer films, tightly encapsulate the fiber surface, forming a dense interfacial transition zone that debonds under load and converts mechanical energy into debonding work. Second, the debonded fiber slides against rough matrix pore walls, dissipating energy as frictional heat during crack opening. Third, when the stress on a bridging fiber exceeds its ultimate tensile strength, the fiber fractures in a flush, brittle break, completing the final stage of energy absorption. Crucially, the team found that this positive toughening mechanism dominates over the pore-related damage, which mainly erodes strength rather than toughness.

The practical upshot is a clear design recommendation: 1 percent glass fiber content delivers the best overall balance of strength, toughness, cost, and pumpability, since higher dosages raise the risk of pipe clogging during spraying. The authors caution that their results come from laboratory-cast specimens, and that fiber orientation, moisture migration, and substrate constraint in real sprayed layers may shift performance, so field validation on rock surfaces remains necessary. Even so, the study delivers something the field has lacked: a quantitative, multi-scale framework that links fiber dosage, pore structure, interfacial micromechanics, and full-process energy dissipation. For engineers contending with squeezing ground and violent rockbursts in ever-deeper tunnels, that framework turns a promising flexible liner into a rationally designed one.

Subject of Research: Multi-scale toughness evaluation and fiber toughening mechanisms in cementitious thin spray-on liners for deep tunnel support

Article Title: Study on multi-scale toughness evaluation and toughening mechanism of fiber-reinforced cementitious thin spray-on liner

Article References: Gao, X., Teng, J., Feng, J., Liu, Y., Ma, L., Bu, X., & Cheng, L. (2026). Study on multi-scale toughness evaluation and toughening mechanism of fiber-reinforced cementitious thin spray-on liner. Case Studies in Construction Materials, 25, Article e06593. https://doi.org/10.1016/j.cscm.2026.e06593

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06593

Keywords: thin spray-on liner, glass fiber reinforcement, cementitious composites, tunnel support, toughness evaluation, energy dissipation, fracture energy, porosity, fiber-matrix interface, deep underground engineering, polymer-modified cement, flexural strength