A new study proves that waste from nickel production isn’t just scrap - it can strengthen concrete, cut emissions, and reshape how we build the world’s next generation of infrastructure.
Study: Performance and statistical characteristics of ferronickel slag geopolymer concrete. Image Credit: Evgeny_V/Shutterstock.com
In a recent study published in the journal Scientific Reports, researchers investigated the performance of ferronickel slag geopolymer concrete (FNS-GC) as a sustainable alternative to conventional concrete. By using ferronickel slag (FNS), an industrial by-product, as a replacement for natural sand, they evaluated its mechanical properties, workability, and overall performance.
The findings highlight FNS-GC’s potential to reduce the environmental impact of construction materials and support the development of more sustainable building practices.
Advancements in Geopolymer Materials
Geopolymer technology represents a new generation of sustainable construction materials. Synthesizing inorganic polymers from aluminosilicate precursors, it provides a greener alternative to Ordinary Portland Cement (OPC) - a major source of carbon emissions, responsible for roughly 5 % of global CO2 output.
Unlike OPC, geopolymers utilize industrial by-products such as fly ash, ground granulated blast furnace slag, and ferronickel slag, significantly cutting waste and emissions. FNS, a by-product of nickel production, offers an additional advantage: it reduces reliance on natural sand, helping conserve depleting natural resources.
Building on this foundation, the study assessed how substituting natural sand with FNS in geopolymer concrete could deliver both structural and environmental benefits.
Designing Ferronickel Slag Geopolymer Concrete: Experimental Framework
Researchers developed FNS-GC by replacing natural sand with FNS at varying rates to evaluate its mechanical and workability characteristics. The experimental setup included 16 mix proportions, varying the aggregate-to-binder (A/B) and water-to-binder (W/B) ratios, along with FNS replacement levels of 0 %, 33 %, 66 %, and 100 %.
The raw materials included S95-grade ground granulated blast furnace slag (GBFS), Class F fly ash (FA), sodium hydroxide (NaOH), sodium silicate (SS), natural coarse aggregate (NCA), and FNS. The alkaline activator was prepared by mixing NaOH with SS to achieve an alkali modulus of 1.20 and allowed to mature before blending.
Standard slump and mechanical strength tests were conducted at curing ages of 3, 14, and 28 days. Additional statistical modeling using normal, log-normal, and Weibull distributions was performed to evaluate compressive strength variability and reliability. Statistical analyses examined the relationship between mix parameters and strength variability, providing insights into the optimal composition for high performance.
Mechanical Strength, Workability, and Microstructural Insights
The incorporation of FNS significantly affected the mechanical and workability properties of geopolymer concrete. Workability tests showed a decline in slump with increasing FNS content, decreasing by 11.58 %, 15.38 %, and 23.08 % at 33 %, 66 %, and 100 % replacement levels, respectively.
This reduction depended on the coarser and angular nature of FNS particles compared to natural sand. At a water-to-binder ratio of 0.45 and an aggregate-to-binder ratio of 3, full replacement resulted in a 23.08 % slump loss relative to the control mix.
Compressive strength demonstrated a nonlinear relationship with FNS content, peaking at a 33 % replacement level with a 28-day strength of 56.36 MPa, about 2.7 % higher than that of the reference mix. Beyond this level, compressive strength declined as excessive FNS reduced matrix compactness and weakened interfacial bonding, indicating that higher replacement rates (>66 %) negatively affected performance.
Splitting tensile strength followed a similar pattern, reaching a maximum of about 4.4 MPa at 33 % FNS. Early-age compressive strength achieved roughly 72 % and 94 % of the 28-day strength at 3 and 14 days, respectively, while tensile strength reached approximately 84 % and 95 % of its 28-day value at the same curing ages.
Microstructural observations using scanning electron microscopy (SEM) revealed that the rough surface of FNS particles promoted stronger mechanical interlocking and improved bonding at the interface between the aggregate and binder, supporting the observed strength trends.
Statistical analysis indicated moderate variability in compressive strength, with coefficients of variation ranging from 0.07 to 0.17, highlighting the importance of precise mix proportioning and quality control.
Among the tested models, the Weibull distribution provided the best fit for compressive strength data, suggesting predictable and reliable performance under varied mix conditions. Overall, partial replacement of natural sand with around 33 % FNS enhanced the performance of geopolymer concrete while maintaining acceptable workability.
Real-World Impact: Sustainable Applications in Construction
This research has significant implications for the construction industry, particularly in advancing sustainable building practices. The use of FNS as a fine aggregate reduces dependence on natural sand while maintaining or slightly enhancing compressive strength at moderate replacement levels. With its high early-age strength, FNS-GC is well-suited for applications that require rapid strength development, such as precast elements and infrastructure projects.
The use of FNS supports circular economy principles by repurposing industrial by-products and minimizing waste. Its improved durability and strength make FNS-GC a viable alternative to conventional concrete for pavements and structural components.
Overall, FNS-based geopolymer concrete offers a practical approach to achieving resource efficiency, waste reduction, and lower carbon emissions. As the construction industry shifts toward greener solutions, geopolymer technology incorporating FNS provides a feasible pathway to long-term sustainability without compromising performance.
Conclusions and the Road Ahead for FNS-Based Geopolymers
In summary, this study evaluates FNS-GC, highlighting its potential as an alternative to conventional materials. The results confirm that partial replacement of natural sand with FNS, primarily at approximately 33 %, enhances the performance of geopolymer concrete while supporting waste utilization and reducing environmental impact.
Future work should focus on assessing the long-term durability of FNS-GC under various environmental conditions, including resistance to sulfate and chloride attack, freeze–thaw cycles, and shrinkage behavior. Optimizing mix designs and predictive modeling of compressive strength will also be crucial to ensure consistent performance.
This research advances the understanding of geopolymer concrete and highlights the role of FNS as a sustainable construction material. By integrating industrial by-products into concrete formulations, FNS-GC offers a practical pathway toward reducing the carbon footprint of construction and promoting environmentally responsible building practices.
Journal Reference
Wang, S., Huang, Q. & Xu, Z. (2025). Performance and statistical characteristics of ferronickel slag geopolymer concrete. Sci Rep 15, 37639. DOI: 10.1038/s41598-025-21614-1, https://www.nature.com/articles/s41598-025-21614-1
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