A carefully optimized dose of basalt fibers could make steel slag-based foamed concrete stronger and far more resistant to freeze–thaw damage, according to new research.
Study: Experimental and microstructural investigation on the strength and frost resistance of basalt fiber reinforced steel slag foamed concrete. Image Credit: Dmitry Markov152/Shutterstock.com
A paper recently published in Scientific Reports presents an experimental and microstructural investigation into the frost resistance and strength of basalt fiber-reinforced steel slag foamed concrete (BFSFC), examining four distinct basalt fiber dosages.
Steel Slag Sustainable Utilization
Steel slag, a by-product of steel production, poses an ongoing environmental challenge due to its continuous accumulation. As a result, substantial research has focused on recycling strategies to enable its effective reuse. One promising pathway is incorporating steel slag into concrete.
Recent studies indicate that integrating solid waste into cement-based composites can help conserve natural aggregates while reducing the environmental footprint of concrete production. In particular, processed steel slag has proven suitable as both a supplementary cementitious material and an aggregate in concrete.
However, balancing environmental sustainability with high material performance remains a key challenge in advanced concrete development.
Steel slag-based foamed concrete has emerged as a potential solution, with early studies confirming the feasibility of using treated steel slag in its production. Despite this promise, the material still faces limitations, including reduced toughness, lower mechanical strength, and increased vulnerability to damage and erosion under freeze–thaw conditions.
Basalt Fiber-Reinforced Foamed Concrete
To address these limitations, researchers have explored fiber reinforcement as a means of improving long-term performance and structural strength. At the same time, the construction industry is increasingly shifting toward sustainable materials, driving interest in natural fibers as alternatives to synthetic options.
Basalt fibers, in particular, stand out due to their high tensile strength and excellent thermal resistance. Previous research suggests that incorporating basalt fibers into steel slag foamed concrete can enhance both durability and mechanical properties. Yet the underlying mechanisms (especially how fiber content influences pore structure, freeze–thaw resistance, and strength) are not yet fully understood.
The Study
In this study, researchers synthesized BFSFC samples with basalt fiber volume fractions of 0 %, 0.15 %, 0.30 %, and 0.45 %. They evaluated compressive and flexural strength, along with resistance to repeated freeze–thaw cycles, to assess the impact of fiber content.
To better understand the material at a microscopic level, scanning electron microscopy (SEM) and X-ray computed tomography (X-CT) were used to analyze internal structures. Micro-void distributions were reconstructed using X-CT and validated with SEM imaging. In addition, grey relational analysis (GRA) was applied to quantitatively link pore characteristics with strength degradation under freezing conditions. This approach helped clarify how fiber content influences microstructure and, in turn, governs mechanical performance and durability.
The materials used included Portland cement (Conch P•O•42.5), finely ground steel slag powder (200-mesh), a plant-based foaming agent, and 12 mm basalt fibers.
Specimens were prepared following JGJ/T 341-2014 standards. The process involved dry-mixing cement and slag, adding water to form a uniform paste, dispersing fibers, and then introducing the foaming agent to create a stable slurry. After casting and a 24-hour setting period, samples were cured at ~95 % humidity and 20 ± 2 °C for 28 days before testing.
Findings
The results indicate that a 0.30 % basalt fiber volume fraction (BFSFC2) delivers the best overall performance. At this level, compressive strength increased by 12.03 % compared to the control, while flexural strength improved by approximately 64 %.
Microstructural analysis revealed that BFSFC2 exhibited a denser and more uniform internal structure. SEM observations showed improved C-S-H gel integration, reduced flaky Ca(OH)2 crystals, and more complete crystallization. The pore system also became more refined, with fewer large pores and a higher proportion of smaller, well-distributed pores.
However, higher fiber dosages led to fiber agglomeration, which introduced defects, increased pore connectivity, and ultimately reduced structural integrity, effectively reversing the benefits.
Freeze–thaw testing further highlighted BFSFC2’s advantages. Strength loss was limited to 8.69 %, compared to 31.14 % in the control sample, while mass loss remained below 5 %, meeting standard requirements. Grey relational analysis showed that fiber content strongly influenced pore network complexity, with a high correlation coefficient of 0.991. This indicates that fractal characteristics of the pore system play a dominant role in governing durability, more so than pore size or shape alone.
Overall, freeze–thaw degradation was primarily driven by pore connectivity and complexity, which affect water movement, saturation, ice formation, and microcrack propagation. The improved performance of BFSFC2 is attributed to its ability to suppress large pore formation and reduce overall pore network complexity, thereby mitigating damage during freeze–thaw cycles.
Conclusion
The study demonstrates that an optimal basalt fiber dosage (specifically 0.30 %) can significantly enhance both mechanical strength and freeze–thaw resistance in steel slag foamed concrete. These findings support a microstructure-driven optimization approach, offering a viable pathway for producing durable, sustainable lightweight concrete suitable for cold-region infrastructure.
Journal Reference
Jiang, J., Chen, M., Yu, X., Jin, Y., & Jiang, W. (2026). Experimental and microstructural investigation on the strength and frost resistance of basalt fiber reinforced steel slag foamed concrete. Scientific Reports. DOI: 10.1038/s41598-026-42606-9, https://www.nature.com/articles/s41598-026-42606-9
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