The research, conducted by Yaser Rashidi and Asghar Habibnejad Korayem, tackled a durability problem that has resisted conventional solutions for decades. When sulfate ions invade cementitious materials, two primary damaging products form. Ettringite arises when alumina-bearing hydrates such as monosulfate and calcium aluminate hydrates react with incoming sulfate in the presence of calcium hydroxide and water. Gypsum forms simultaneously through cation-exchange reactions between sulfates and calcium hydroxide. Both phases occupy greater solid volume than the phases they replace, so the matrix expands, cracks, and then admits even more sulfate in a self-accelerating feedback loop. Over time the cohesion of the hydration products collapses, and strength and mass drain away.

Engineers have traditionally fought back along three fronts: limiting the reactive tricalcium aluminate content of cement as in ASTM C150 Type II and Type V sulfate-resistant cements, blending in supplementary cementitious materials such as fly ash, slag, metakaolin, and silica fume to consume calcium hydroxide pozzolanically, and reducing permeability through lower water-to-binder ratios or fine mineral additives that tighten the pore network. Each strategy helps, but none fully solves the problem, because residual calcium hydroxide remains available for gypsum formation, and even well-refined matrices still transport ions. Nanoparticles promised a fourth front, yet materials such as nano-silica, carbon nanotubes, and graphene oxide carry significant production costs and environmental burdens, and their effectiveness depends critically on achieving good dispersion.

That is where halloysite nanotubes stand out. With outer diameters of roughly 30 to 70 nanometers and lengths of 1 to 3 micrometers, these natural tubes have enormous specific surface area, around 640,000 square centimeters per gram in this study, and an aluminosilicate composition of about 48 percent silica and 35 percent alumina. They act on cement through three complementary mechanisms: physical filling of the fine interstitial spaces between cement grains, heterogeneous nucleation that gives hydration products abundant surfaces on which to grow, and gradual pozzolanic reactions that consume calcium hydroxide and generate additional calcium silicate hydrate gel. Unlike carbon nanotubes or graphene oxide, they require no energy-intensive synthesis, chemical oxidation, or high-temperature functionalization; they are simply mined and processed.

A crucial subtlety the researchers confronted is that nanoparticles tend to clump in the brutal environment of cement pore solution. With a pH of 13.1 to 13.5 and a high concentration of dissolved ions, the synthetic pore solution used in the study compresses the electrical double layers around particles, collapsing the electrostatic repulsion that keeps them apart. Without help, ultrasonication only temporarily breaks agglomerates apart; they re-form within hours. The team’s answer was polycarboxylate ether, or PCE, the same high-range water-reducing admixture routinely used to fluidize concrete. PCE molecules adsorb onto halloysite surfaces through their anionic functional groups while their long polyethylene glycol side chains form a steric barrier, physically preventing neighboring tubes from touching.

The dispersion experiments were elegant in their design. Suspensions matching the dosages used in the mortars were mixed 1:1 with synthetic pore solution and tracked by visual sedimentation, ultraviolet-visible spectroscopy, and dynamic light scattering. The results were unambiguous. Without PCE, the suspension’s normalized UV-Vis absorbance collapsed from 1.0 to just 0.04 within six hours, and its average hydrodynamic particle diameter ballooned from 972 to 2,750 nanometers as particles aggregated and settled. With PCE, absorbance stayed high and particle growth was minimal, with the two lower-dose suspensions growing only from about 409 to 513 and 486 to 578 nanometers respectively. The highest-dose suspension, corresponding to 3 weight percent HNTs, showed slightly reduced stability, an early warning sign that would echo in the mortar performance.

The mortars themselves told the rest of the story. Replacing 1, 2, or 3 weight percent of ordinary Portland cement with PCE-stabilized HNTs, at a fixed water-to-binder ratio of 0.4 and identical workability, the researchers exposed mortar bars and cubes to a 5 percent sodium sulfate solution for 182 days following ASTM C1012. The plain reference mortar expanded by 0.084 percent over 26 weeks, above the 0.05 percent threshold that ASTM C1157 classifies as non-resistant to sulfate. The 1 percent HNT mixture fared little better at 0.080 percent. But the 2 and 3 percent mixtures stayed below the threshold at 0.032 and 0.043 percent respectively, a genuinely high level of sulfate resistance achieved purely by a clay additive.

The mechanical evidence was equally compelling. Before exposure, compressive strengths rose from 42.6 megapascals in the reference to 52.9 megapascals with 2 percent HNTs. After 182 days of sulfate immersion, the reference mortar had lost 18.8 percent of its compressive strength and a striking 29.9 percent of its flexural strength, while its ultrasonic pulse velocity, a proxy for internal integrity, dropped 9.6 percent. The 2 percent HNT mortar lost only 5.2 percent compressive and 13.1 percent flexural strength, and its pulse velocity actually increased by 3.3 percent, meaning sulfate products filling refined pores left it more acoustically dense than before. Scanning electron microscopy revealed denser, crack-poor microstructures before exposure and far fewer needle-like ettringite crystals afterward. X-ray diffraction showed progressively weaker ettringite and gypsum peaks with increasing HNT content, and Fourier-transform infrared spectra confirmed the pattern: weaker sulfate-related bands at 1110, 670, and 550 inverse centimeters, and a stronger calcium silicate hydrate band at 982.

Why does a humble clay tube outperform? The authors attribute it to synergy. Chemically, diluting the clinker reduces the reactive aluminate supply, while pozzolanic consumption of calcium hydroxide starves both the gypsum and ettringite reactions of raw material. Physically, the tubes pack into pores, nucleate hydration, and even act as internal water reservoirs whose hydrophilic bores release moisture gradually to sustain curing. The result is a matrix whose pore connectivity is so reduced that sulfate ions simply cannot reach their targets in damaging quantities. The one caveat is dosage discipline: at 3 weight percent, agglomeration created weak zones, and every measured property slipped slightly below the 2 percent optimum, a direct macroscopic echo of the dispersion tests.

Perhaps the most consequential finding is the sustainability comparison. Compiled literature data show halloysite carrying a global warming potential of roughly 5 to 6.6 kilograms of carbon dioxide equivalent per kilogram, versus 28.55 for carbon nanotubes produced by chemical vapor deposition and 8.55 for graphene oxide, and an embodied energy of about 21 megajoules per kilogram versus 480 for CNTs and 120 to 140 for graphene oxide. At around 0.7 dollars per kilogram, HNTs cost less than a tenth of nano-silica and a tiny fraction of carbon-based alternatives. For a construction industry desperately seeking durable, low-carbon materials, the message is remarkable: a naturally abundant clay mineral, stabilized by an admixture already in every ready-mix truck, can match the sulfate resistance of engineered nanomaterials while leaving a fraction of their environmental and economic footprint. The next generation of sulfate-proof infrastructure may literally be dug from the ground.

Subject of Research: Use of halloysite nanotubes to enhance the sulfate resistance and sustainability of cementitious composites

Article Title: Sustainable halloysite nanotubes for sulfate–resistant cementitious composites: Physicochemical mechanisms and environmental advantages

Article References: Rashidi, Y., & Korayem, A. H. (2026). Sustainable halloysite nanotubes for sulfate–resistant cementitious composites: Physicochemical mechanisms and environmental advantages. Case Studies in Construction Materials, 25, Article e06582. https://doi.org/10.1016/j.cscm.2026.e06582

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06582

Keywords: halloysite nanotubes, sulfate attack, cement mortar, durability, nanomaterials, ettringite, gypsum, pozzolanic reaction, polycarboxylate ether, sustainable construction, pore refinement, embodied energy

The threat itself operates through two intertwined mechanisms. The first is physical: sulfate solutions penetrate the porous network of cement through capillary action and osmosis, and as temperature and humidity fluctuate, dissolved sulfates reach supersaturation and crystallize inside capillary pores, voids, and micro-cracks. Growing crystals press relentlessly against pore walls, and once that pressure exceeds the internal cohesion of the matrix, pores expand and coalesce, the framework loosens, and surfaces begin to crack, peel, and powder. This damage opens fresh pathways for more sulfate ingress, creating a self-reinforcing cycle of erosion, deterioration, and accelerated erosion. The second mechanism is chemical and far more destructive. Sulfate ions react with calcium hydroxide to form gypsum and with calcium aluminates to generate ettringite—two expansive products that swell to roughly twice and one-and-a-half times their original volume, respectively. In the cramped interior of hardened cement, this expansion generates internal stresses that break chemical bonds between hydration products, raise porosity, propagate cracks, and ultimately strip away compressive strength, rupture strength, and interfacial bonding capacity.

Earlier work had already hinted that nanomaterials could help. Studies cited by the team showed that 1.5% nano-SiO₂ boosted the rupture strength of fly ash-cement mortar by 90%, while 0.5% raised compressive strength by 67.1% to 118.2%, and that 1% nano-CaCO₃ refined concrete’s microstructure enough to mitigate late-stage expansion damage. But nanomaterials carry a notorious drawback: their ultrafine particle size and enormous specific surface area make them prone to agglomeration during mixing, which raises water demand, degrades workability, and can undermine the very strength they are meant to enhance. The new research set out to resolve this tension by systematically comparing both nanoparticles across multiple dosages, combining macroscopic measurements of mass, compressive strength, and rupture strength with microscopic characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR).

The experimental design was rigorous and methodical. Seven mortar groups were prepared with a water-to-cement ratio of 0.55: an unmodified control, three groups with nano-SiO₂ at 1%, 3%, and 5% by mass of cement, and three groups with nano-CaCO₃ at the same dosage levels. The nano-SiO₂ particles measured about 20 nanometers with a specific surface area of 80 square meters per gram, while the nano-CaCO₃ particles were roughly 40 nanometers with 30 square meters per gram. After 28 days of standard curing and drying at 80 degrees Celsius, the 40 by 40 by 160 millimeter prisms were fully immersed in a 5% sodium sulfate solution at 20 degrees Celsius, with the solution renewed every 30 days to maintain stable concentration and pH. Specimens were retrieved at 30, 60, 90, 120, 150, and 180 days for testing, with three parallel specimens averaged for each measurement.

The mass evolution told a striking story. All groups first gained weight as invading sulfate reacted with hydration products to form pore-filling ettringite and gypsum, then lost weight as excessive expansion triggered micro-cracking, surface spalling, and detachment of erosion products. The nano-SiO₂ group at 3% dosage peaked at a 4.39% mass gain at 90 days and still retained a 3.70% mass change at 180 days, losing only 0.69% after its peak. By contrast, the 5% nano-CaCO₃ group reached a slightly higher peak of 4.55% but then shed a full 3.55% of its mass in the same window, ending at roughly 1%. After 180 days, the optimal nano-SiO₂ group’s mass change was 122.9% higher than that of the optimal nano-CaCO₃ group—a quantitative demonstration that the mass gained by nano-SiO₂ modification reflects a dense, penetration-resistant matrix, whereas the mass gained by heavily dosed nano-CaCO₃ stems from expansive ettringite that later causes severe spalling.

Compressive and rupture strength followed a three-stage trajectory of initial rise, mid-term plateau, and final decline, with peaks generally appearing between 30 and 90 days as ongoing hydration gave way to expansion damage. The 5% nano-SiO₂ group posted the highest peak compressive strength of 55.59 megapascals at just 30 days, while the 3% nano-SiO₂ group peaked at 51.47 megapascals. Crucially, strength retention revealed the deeper advantage of nano-SiO₂: at both the 1% and 3% dosage levels, nano-SiO₂-modified specimens retained more of their peak strength than their nano-CaCO₃ counterparts, with the 1% nano-SiO₂ group preserving 75% of its peak compressive strength after 180 days compared with 65.4% for the equivalent nano-CaCO₃ group. In rupture strength, the 3% nano-SiO₂ group held a retention rate of 44.4% versus 34.2% for 3% nano-CaCO₃, and its residual strength of 1.82 megapascals clearly exceeded the control group’s 1.65 megapascals. The team attributes this resilience to nano-SiO₂’s dual action: its pozzolanic reaction chemically consumes calcium hydroxide—the very ingredient sulfate ions need to form gypsum—while its micro-aggregate filling effect physically blocks ion transport channels.

The microscopic evidence sealed the argument. X-ray diffraction showed that in the unmodified control, ettringite and gypsum peaks surged between 90 and 120 days, reached maximum intensity by 150 to 180 days, and were joined by thaumasite, a notoriously destructive sulfate-bearing phase, marking the onset of accelerated deterioration. The 1% nano-SiO₂ group, by contrast, showed the lowest ettringite and gypsum peak intensities of all groups throughout the 90-to-180-day window and no obvious thaumasite signal at all, because the pozzolanic reaction had stripped the system of the calcium hydroxide needed to fuel attack reactions. Scanning electron microscopy at 10,000-fold magnification made the damage hierarchy visible: after 180 days, the control mortar displayed interconnected crack networks, spalling, and a failed hydration skeleton, while the 3% nano-SiO₂ specimen maintained a complete, continuous gel skeleton with only trace surface attack products. The overall degradation ranking ran from worst to best as control, 5% nano-CaCO₃, 3% nano-CaCO₃, 1% nano-CaCO₃, 1% nano-SiO₂, 5% nano-SiO₂, and 3% nano-SiO₂.

Nuclear magnetic resonance added a non-destructive, quantitative dimension by tracking pore size distribution through the relaxation behavior of hydrogen nuclei in pore water. At the outset, all nano-modified samples already showed lower initial porosity than the control’s 11.41%, thanks to nanoparticle filling. Porosity then fell during the first 90 days as expansive products temporarily plugged capillary channels—the 5% nano-SiO₂ group plummeting from 10.16% to a remarkable 3.97%—before rebounding after 120 days as expansion stress cracked the matrix. By 180 days, the control’s porosity had climbed back to 11.12%, nearly erasing its early densification, while the nano-modified specimens showed far smaller rebounds. Classifying pores by the widely used Wu Zhongwei system, the researchers found that the fractions of harmful pores (50 to 200 nanometers) and severely harmful pores (above 200 nanometers) grew most dramatically in the control group and most slowly in the 5% nano-SiO₂ group, whose T₂ spectra shifted least and whose harmless pore fraction remained the highest throughout.

The study’s practical verdict is nuanced: the optimal dosage depends on which performance indicator matters most. For nano-SiO₂, 3% proved best for mass stability while 5% excelled in compressive strength, rupture strength, and porosity, leading the team to recommend a 3% to 5% window. For nano-CaCO₃, 1% was optimal for mass and mechanical properties, and although 5% minimized porosity, SEM images showed clustered ettringite enrichment at that dose, with expansion stress initiating micro-cracks that no amount of physical filling could offset—so 1% stands as the overall recommendation. The fundamental difference lies in mechanism: nano-SiO₂ fights sulfate attack on two fronts, chemically through pozzolanic conversion of calcium hydroxide into dense calcium-silicate-hydrate gel and physically through pore refinement, while nano-CaCO₃ works mainly through nucleation and filling. For engineers designing structures destined for sulfate-laden coastlines, saline soils, or aggressive industrial environments, the message is clear: a few well-chosen nanometers of silica, added at just the right fraction, can mean the difference between a structure that crumbles within decades and one that endures for generations.

Subject of Research: Sulfate resistance of cement-based materials modified with nano-SiO₂ and nano-CaCO₃ nanoparticles

Article Title: Optimum dosage and long-term sulfate resistance of cement-based materials modified by nano-SiO₂ and nano-CaCO₃

Article References: Hao, E., Yuhang, L., Zhang, D., Wang, J., Ya, G., Wang, X., & Cao, Y. (2026). Optimum dosage and long-term sulfate resistance of cement-based materials modified by nano-SiO₂ and nano-CaCO₃. Case Studies in Construction Materials, 25, Article e06585. https://doi.org/10.1016/j.cscm.2026.e06585

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06585

Keywords: sulfate attack, nano-SiO2, nano-CaCO3, cement-based materials, concrete durability, ettringite, gypsum, pozzolanic reaction, pore structure, NMR, XRD, SEM

The study, carried out by Habtamu Admas and Tesfahun Kassahun of Injibara University and published in Environmental Earth Sciences, tested two complementary strategies for reclaiming salt-affected soils across two experimental sites in Asaita District, roughly 670 kilometers northeast of Addis Ababa. The first strategy was biological: growing salt-tolerant forage species, alone and in combination with filter-cake compost, a byproduct of sugar processing rich in organic matter and nutrients. The second was chemical-organic: applying gypsum, a calcium sulfate mineral, at rates of zero, five, and ten tonnes per hectare, factorially combined with the same compost rates. Both experiments were laid out in randomized complete block designs with three replications, producing 54 plots in total under genuine farmers’ field conditions rather than the more forgiving environment of a research station.

The chemistry behind the approach is elegantly simple. Salinity, measured as electrical conductivity, reflects the concentration of soluble salts, chiefly chlorides and sulfates of sodium, calcium, and magnesium, that raise the osmotic stress on plants and impair their ability to take up water. Sodicity is a different problem altogether: an excess of sodium ions clinging to the soil’s cation-exchange sites, where they cause clay particles to disperse, aggregates to collapse, and water infiltration to grind to a halt. Gypsum attacks the sodic half of the problem directly. When it dissolves, its calcium ions swap places with sodium on the exchange complex, releasing sodium into the soil solution, where a well-managed irrigation and drainage system can flush it below the root zone. Compost, meanwhile, works on the physical side, feeding microbes, building aggregates, improving porosity, and releasing its own basic cations that help displace sodium.

The results at the second experimental site, where baseline conditions were more severely degraded with an electrical conductivity of 7.1 decisiemens per meter and an exchangeable sodium percentage of 19.2 percent, delivered the study’s most striking numbers. The combined application of ten tonnes per hectare of gypsum and ten tonnes per hectare of filter-cake compost reduced electrical conductivity from 6.56 to 2.85 decisiemens per meter, a drop of 56.6 percent, and cut the exchangeable sodium percentage from 13.17 to 5.79 percent, a reduction of 56.0 percent. Soil pH fell by 0.60 units, from 8.25 to 7.65, pushing the soil out of strongly alkaline territory. Exchangeable sodium dropped from 9.64 to 4.61 centimoles of charge per kilogram, and bulk density, a key indicator of soil compaction, fell from 1.37 to 1.01 grams per cubic centimeter, signaling a soil that had reopened its pore spaces to water and roots.

Just as importantly, the integrated treatment improved the soil’s capacity to hold and exchange nutrients. Cation exchange capacity, a measure of the soil’s ability to retain positively charged nutrients, rose from 73.2 to 79.6 centimoles of charge per kilogram under the combined gypsum-compost treatment. Total nitrogen, organic carbon, available phosphorus, and available sulfur all increased relative to the untreated control, and extractable micronutrients including iron, manganese, zinc, copper, and boron rose in parallel, a critical finding in alkaline soils where these elements are often locked away from plant roots. The authors attribute these gains to the mineralization of nutrients from the compost by soil microbes and to the improved root environment created as sodium was displaced and leached.

At the first experimental site, where the biological approach was tested, Blue panic grass (Panicum antidotale) combined with ten tonnes per hectare of compost proved the standout performer, producing the lowest bulk density at 1.01 grams per cubic centimeter and the lowest pH at 7.77, compared with 1.31 grams per cubic centimeter and 8.32 in the untreated control. Plots planted with Sesbania sesban and the same compost rate recorded the lowest electrical conductivity among the forage treatments, at 3.17 decisiemens per meter against 9.5 in the control, alongside the lowest exchangeable sodium percentage at 6.29 percent. The mechanism is part extraction and part facilitation: deep-rooted, salt-tolerant plants absorb sodium and other salt ions through their tissues, while their roots and the decomposing compost open channels for water to move dissolved salts downward, out of the root zone.

The broader context makes these findings more than an academic curiosity. Soils developed from volcanic and lacustrine deposits in the Awash valley include substantial areas of Solonetz, Solonchaks, and other salt-affected units, and agriculture in Asaita depends almost entirely on irrigation because rainfall is too erratic to support reliable rain-fed cropping. Mean monthly evapotranspiration in the area ranges from 222 millimeters in November to 375 in July, a relentless evaporative pump that concentrates salts at the soil surface. In a region where roughly 90 percent of the Afar population depends on livestock and small-scale irrigated cropping along river basins, each hectare lost to salinity directly undermines household income and regional food security. The forage-based reclamation route carries a bonus: the grasses and legumes themselves become fodder for penned animals, turning a remediation cost into a source of income.

The study is also candid about its limits. The researchers calculated gypsum requirements using a standard formula based on cation exchange capacity, actual and target exchangeable sodium percentages, bulk density, and reclamation depth, applying rates appropriate to the upper 30 centimeters of soil. Adequate drainage was maintained throughout, which the authors stress is essential; without it, the sodium displaced by gypsum would simply accumulate again. They note that available phosphorus actually declined at the highest gypsum rates, likely because abundant calcium ions react with phosphate to form less-soluble calcium phosphate compounds, a trade-off that farmers and agronomists will need to manage. The irrigation water’s own electrical conductivity and sodium adsorption ratio were not recorded, and no combined statistical analysis across the two sites was possible because the experiments had different treatment structures.

Perhaps the most important caveat concerns scale. The authors explicitly warn that the findings should not be generalized to the entire Afar Region, since soil properties, irrigation conditions, and agro-ecological characteristics vary considerably from place to place. They also flag that the economic assessment in the study is qualitative rather than a formal cost-benefit analysis, and that the viability of hauling gypsum and compost to remote fields will depend on local prices, transport distances, and labor. Still, both raw materials have appealing characteristics: filter cake is an agro-industrial residue that would otherwise require disposal, it contains 1.5 to 2.0 percent nitrogen, 0.8 to 1.2 percent available phosphorus, and 1.2 to 1.8 percent potassium with a favorable carbon-to-nitrogen ratio, and its low electrical conductivity and near-neutral pH make it safe for use on already salt-stressed land.

For a world losing farmland to salt at an accelerating pace as irrigation expands and climates dry, the Asaita results offer a concrete, field-verified recipe: where salinity and sodicity co-occur, neither gypsum alone nor compost alone is enough, but ten tonnes per hectare of each, applied together under sound irrigation and drainage, can push a degraded saline-sodic soil back toward productivity within a single growing season. The recommendation carries a condition, not a promise. It works where water can be applied in the right amounts and drained away, carrying the displaced sodium with it. In the Lower Awash Basin, where the river supplies the water and the desert supplies the heat, that combination of chemistry, biology, and careful water management may be the most practical lifeline available to the farmers watching their fields turn white.

Subject of Research: Field evaluation of gypsum and compost amendments for reclaiming saline-sodic soils in Asaita District, Northeastern Ethiopia

Article Title: Application of compost and gypsum to improve physicochemical properties of saline-sodic soil conditions in Asaita District, Northeastern Ethiopia

Article References: Admas, H., & Kassahun, T. (2026). Application of compost and gypsum to improve physicochemical properties of saline-sodic soil conditions in Asaita District, Northeastern Ethiopia. Environmental Earth Sciences, 85(16), Article 408. https://doi.org/10.1007/s12665-026-13143-5

Image Credits: AI Generated

DOI: 10.1007/s12665-026-13143-5

Keywords: soil salinity, sodicity, gypsum, compost, saline-sodic soil, soil reclamation, phytoremediation, Lower Awash Basin, Ethiopia, soil physics, soil chemistry, irrigated agriculture