The research, led by Atchaya Sowmiyan under the supervision of Parukutty Sanker Ambily, with Senthil Kumar Kaliyavaradhan as corresponding author, tackles one of the most demanding corners of modern construction technology. Three-dimensional printable concrete, often abbreviated 3DPC, is not ordinary concrete. It must flow smoothly through a nozzle, hold its shape the instant it emerges, and support the weight of successive layers without slumping or deforming. Balancing these competing demands is difficult even with conventional materials, and introducing an industrial by-product as a full replacement for sand risks upsetting the delicate rheological equilibrium that makes extrusion-based printing possible.

To test whether copper slag could meet the challenge, the team formulated three mixes. The reference mix, designated RS-BM, used river sand as the fine aggregate. Two further mixes replaced the sand completely with copper slag, one on a volume-for-volume basis, designated CS-VR, and the other on a weight-for-weight basis, designated CS-WR. Because copper slag is denser than river sand, the distinction between volume and weight replacement matters considerably: it changes the total volume of paste available to coat and lubricate the particles, which in turn alters flow, cohesion and the ability of the fresh material to bond layer upon layer.

The researchers evaluated the fresh, or unhardened, properties of each mix across the full suite of criteria that govern printability. These included rheology, the science of how the material flows under stress; flowability, a measure of how readily the mix spreads; extrudability, its ability to pass continuously through the printing nozzle; open time, the window during which the mix remains printable after mixing; and buildability, its capacity to sustain stacked layers without collapse. Each of these properties must fall within a narrow band. A mix that flows too easily will produce weak, slumping layers, while one that is too stiff will clog the printer and leave gaps between filaments.

The results were encouraging for the volume-replacement mix in particular. CS-VR maintained desirable flow and slump characteristics, and its printability and stability were consistent with those of the river sand reference. Most strikingly, the copper slag mix printed by volume replacement exhibited the longest open time of the three formulations and superior buildability, with minimal shape deformation as layers accumulated. In practical terms, a longer open time gives operators a wider safety margin between batching and printing, reducing waste and allowing larger or slower prints, while high buildability permits taller structures before the material at the base becomes overloaded.

The rheological analysis added a quantitative layer to these observations. The team fitted their flow measurements to mathematical models describing how stress relates to shear rate in the fresh material, and found that the Modified Bingham model best represented the dynamic yield stress, the threshold stress that must be exceeded before the concrete begins to flow. Dynamic yield stress is a central parameter in 3D printing: it must be low enough for smooth extrusion yet high enough for the extruded filament to retain its shape. The CS-WR mix, in which copper slag replaced sand by weight, consistently showed the highest dynamic yield stress values of the three mixes, indicating robust printability and strong structural integrity in the fresh state.

Viscosity measurements across a range of shear rates revealed another important characteristic: all three mixes displayed shear-thinning behaviour, meaning their viscosity decreased as the rate of shear increased. This is precisely the property a printable concrete needs. Inside the nozzle and pump, where shear rates are high, the material flows readily; once deposited on the print bed and left at rest, it thickens and holds its form. Interestingly, the river sand reference mix exhibited higher initial viscosity than either copper slag formulation, suggesting that the glassy, smooth-textured slag particles may reduce internal friction in the fresh paste, easing the material’s journey through the printing system.

Beyond the laboratory performance figures, the environmental logic of the substitution is compelling. Copper slag accumulates as a waste stream in smelting regions, occupying land and posing potential leaching concerns, while river sand extraction has become a global sustainability crisis, with construction demand depleting waterways and coastlines. A concrete that consumes slag instead of sand addresses both burdens simultaneously. The authors conclude that copper slag-based mixes, in both their volume-replacement and weight-replacement forms, offer potential benefits over river sand mixes for 3D printable concrete in terms of material performance as well as environmental impact, positioning the by-product not as a compromise but as an upgrade.

The study also fits into a broader movement within digital fabrication research, in which groups worldwide have explored recycled brick powder, waste glass, construction and demolition debris and other secondary streams as aggregates for printed concrete. What distinguishes the present work is the achievement of full replacement, rather than partial substitution, while preserving the fresh-state properties that printing demands. The work was carried out at the CSIR-Structural Engineering Research Centre in Chennai and funded by the Council of Scientific and Industrial Research, New Delhi, with the first author completing the investigation as an M.Tech thesis project.

For the construction industry, the findings arrive at a moment when 3D printing is moving from experimental pavilions to housing projects, and when regulators in sand-stressed countries are tightening restrictions on riverbed mining. If copper slag can reliably replace river sand in printable mixes, printers could draw on an abundant industrial residue to build walls, homes and infrastructure with a smaller ecological footprint. The Chennai team’s results, demonstrating stable extrusion, extended open time, high buildability and favourable rheology with minimal deformation, provide the fresh-property evidence base that engineers need before such mixes can advance to structural trials and, ultimately, to printed buildings that turn smelter waste into shelter.

Subject of Research: Use of copper slag as a fine aggregate replacement for river sand in 3D printable concrete

Article Title: Effect of copper slag as fine aggregate on the fresh properties of 3D printable concrete

Article References: Sowmiyan, A., Ambily, P. S., Kaliyavaradhan, S. K., Ayyanarsamy, V., & Shekar, D. (2026). Effect of copper slag as fine aggregate on the fresh properties of 3D printable concrete. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38239-0

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38239-0

Keywords: 3D printable concrete, copper slag, river sand, rheology, buildability, extrudability, open time, dynamic yield stress, shear-thinning, sustainable construction, fine aggregate, industrial by-products

Water-based drilling fluids are the workhorses of well construction. They carry rock cuttings out of the borehole, stabilize the wellbore against collapse, control formation pressures, lubricate the drill string, and minimize damage to the productive formations encountered along the way. The performance of these fluids depends heavily on bentonite, a clay dominated by sodium montmorillonite, whose remarkable swelling capacity, thixotropic behavior, and ability to form thin, low-permeability filter cakes make it the industry’s standard viscosifying and filtration-control agent. Yet despite Nigeria’s extensive clay deposits spread across several geological formations, most local clays perform poorly compared with commercial bentonite, forcing operators to rely on imports whose prices and availability fluctuate with global supply conditions.

Previous attempts to replace imported bentonite entirely with local clays have demanded extensive chemical beneficiation or high dosages of synthetic additives to meet API specifications, strategies that introduce operational risks and drive up treatment costs. The research team, led by Lawrence Ifeanyi Igbonekwu, took a different and more pragmatic path: partial replacement. Building on an earlier study in which several beneficiation routes were tested on Nteje clay from Anambra State, the researchers selected the Na₂EDTA/NaCl sodium-saturation treatment, designated NC3, as the most effective upgrade of the raw material. The new study set out to answer an entirely different engineering question: how far can this beneficiated clay go as a bentonite extender before drilling-fluid performance begins to fail?

To find out, the team formulated mud samples at a constant total clay concentration of 22 grams per laboratory barrel, dispersing the clay blends in 350 milliliters of distilled water and mixing them with a five-spindle multimixer before allowing 24 hours of hydration. Imported bentonite was progressively substituted by NC3 in eleven formulations ranging from 0 to 100 percent replacement. All rheological and filtration measurements followed the recommended procedures of API RP 13B-1, using a Fann Model 35A rotational viscometer for dial readings at standard speeds and a Fann Model 300 low-temperature low-pressure filter press operated at 100 psi for 30 minutes. This rigorous standardization allowed the researchers to judge every blend against well-established API screening criteria.

The rheological results revealed a clear and systematic pattern. The 600 rpm viscometer reading, a key indicator of high-shear viscosity, declined steadily from 53 centipoise for the pure bentonite mud to 31 centipoise at 60 percent NC3 substitution, still above the API minimum requirement of 30 centipoise, before collapsing to just 13 centipoise in the fully local system. Plastic viscosity, which reflects internal friction from solid particles, remained in the stable range of 8 to 10 centipoise for blends containing up to 50 percent NC3, indicating that moderate substitution does not upset the mechanical structure of the fluid. Yield point, the minimum stress needed to initiate flow, fell from 33 to 13 pounds per 100 square feet over the same span, while the yield point to plastic viscosity ratio, an important measure of cuttings-carrying capacity, stayed within the recommended screening range of 0.75 to 3.0 at the 50 and 60 percent substitution levels.

Shear-thinning behavior, the hallmark of a well-designed drilling fluid, persisted across the blended formulations. The flow behavior index derived from viscometer data remained low for bentonite-rich systems, signaling strong pseudoplasticity, and rose only gradually as NC3 content increased. This matters because shear-thinning fluids suspend cuttings effectively at low shear when circulation stops, yet flow readily and impose lower frictional pressure losses at high shear during pumping. Gel strength measurements told a similar story: moderate NC3 additions produced sufficient structural buildup to hold cuttings and weighting materials in suspension without creating the punishing pump pressures that accompany circulation restarts, while NC3-rich systems showed weakened gels that raised the risk of solids settling and barite sag under static conditions.

Filtration performance proved to be another decisive screening criterion. API fluid loss climbed steadily with NC3 content, from 8 milliliters for the base mud to 14 milliliters at 60 percent substitution, remaining under the API maximum of 15 milliliters. Beyond that threshold the losses escalated rapidly, reaching 18.3 milliliters in the fully local formulation, a 22 percent breach of the specification. Filter cake thickness followed the same trajectory, staying below 2 millimeters up to the 60 percent level but ballooning to 3.2 millimeters at full replacement. Thick, permeable cakes increase the danger of differential sticking and elevate torque and drag on the drill string, so the team photographed the cakes from the recommended blends and confirmed that they were thin and compact, measuring just 1.7 and 1.9 millimeters at the 50 and 60 percent levels respectively.

Material characterization helped explain why the clays behave so differently. X-ray fluorescence showed that both materials are dominated by silica and alumina, confirming their aluminosilicate framework, with NC3 containing 61.70 percent SiO₂ and 17.80 percent Al₂O₃ compared with 59.95 and 19.20 percent for the imported bentonite. However, X-ray diffraction revealed that NC3 is dominated by quartz with calcite, cristobalite, zeolitic phases, and iron-bearing minerals, whereas the imported bentonite displayed the characteristic montmorillonite peaks that underpin its swelling and viscosifying power. Scanning electron microscopy reinforced the contrast: the foreign bentonite exhibited the layered platelet morphology that facilitates water adsorption, interlayer expansion, and viscosity development, while NC3 showed a denser, less ordered surface. The researchers also noted that pH increased with NC3 content and that only the fully local blend met the API minimum pH of 9.5, suggesting that modest alkalinity control may be needed at lower substitution levels.

The economic analysis may prove to be the study’s most persuasive element. Using a weighted-average clay cost model scaled from the laboratory barrel to estimated well-level clay consumption, the researchers calculated that the base formulation would cost about USD 10,875 per well in clay materials alone. Blending at 50 percent NC3 reduced that figure to USD 7,312, a 33 percent saving, and at 60 percent substitution the cost fell to USD 6,600, roughly 39 percent below the import-dependent baseline. Higher substitution levels promised even deeper savings, up to 65 percent, but those gains came hand in hand with fluid losses, weak gels, and near-Newtonian flow behavior that would jeopardize drilling operations. The sweet spot, the study concludes, is the 50 to 60 percent replacement range, where API-compliant rheology and filtration coexist with substantial cost reductions.

The authors are careful to frame their findings within the limits of laboratory screening under standard test conditions; high-pressure high-temperature environments and field-scale validation remain open questions. Even so, the work delivers a practical framework for turning indigenous clay resources into industrial assets: beneficiate the local material, screen it against API performance criteria in hybrid blends, and quantify the raw material economics before committing to field trials. For a developing oil-producing nation spending scarce foreign exchange on imported bentonite, the message is striking. The mud that drills the wells of tomorrow may not need to cross an ocean first; it may be sitting, quietly, in the red earth of Anambra State, waiting to be blended in the right proportion.

Subject of Research: Experimental evaluation of beneficiated Nteje clay as a partial replacement for imported bentonite in water-based drilling fluid formulations.

Article Title: Experimental screening of beneficiated Nteje clay–bentonite blends for water-based drilling fluid formulations

Article References: Igbonekwu, L. I., Nwabanne, J. T., Abonyi, M. N., & Ezechukwu, M.-J. C. (2026). Experimental screening of beneficiated Nteje clay–bentonite blends for water-based drilling fluid formulations. Discover Geoscience, 4(1), Article 370. https://doi.org/10.1007/s44288-026-00738-5

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00738-5

Keywords: water-based drilling fluid, bentonite replacement, Nteje clay, rheology, filtration, drilling mud, Nigeria, clay beneficiation, shear-thinning, raw material cost analysis, API standards, oil and gas drilling