Engineers have uncovered the material combinations that help concrete resist cracking, corrosion, and structural fatigue.
Study: Tensile characterization of high-performance fibre-reinforced concrete: effect of steel or amorphous metallic fibres and of cement type. Achira22/Shutterstock.com
The new study in Materials and Structures explores how different fiber types and cement compositions influence the tensile behavior of high-performance fiber-reinforced concrete (HPFRC).
Using advanced modeling and mechanical testing, researchers evaluated three concrete mixes combining either straight steel or amorphous metallic fibers with CEM I or CEM III cement. Their goal was to design sustainable concrete capable of resisting cracking and degradation in aggressive environments.
HPFRC is a useful material due to its ability to control cracking under tension, extend service life, and reduce maintenance requirements.
By embedding fibers into the cementitious matrix, these high-performance materials increase ductility and enable stable microcrack propagation. This is especially important at the serviceability limit state (SLS), where concrete experiences sustained tensile stresses.
The combination of fine crack control and autogenous self-healing enhances durability even in harsh exposure conditions, such as those found in marine or geothermal environments.
A Comparison of High-Performance Cements
The research focused on three mixes: a reference mix using steel fibers and CEM I cement; a variant using amorphous metallic fibers instead of steel; and a third mix using CEM III cement with steel fibers. All contained 1.5% fiber by volume.
Specimens were cast as deep beams (100 × 100 × 500 mm3) and thin beams (100 × 25 × 500 mm3) to simulate structural applications like precast geothermal tanks.
After curing for 90 days, they were tested using four-point bending (4PBT), double-edge wedge splitting (DEWS), and inverse analysis to derive tensile behavior.
The inverse analysis method, validated for deep beams, was used to estimate stress-strain and stress-crack opening laws. Thin beam and DEWS results were compared to those derived from inverse modeling, though those comparisons were exploratory.
The team also used a hinge model to simulate bending behavior based on the tensile laws.
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Key Findings on Tensile Behavior
The mixes displayed similar tensile strengths, ranging from 8 to 9 MPa, but showed clear differences in ductility and post-cracking behavior:
- Steel fiber mixes achieved strain-at-localization values between 2.9 % and 3.5 %, exceeding the 2.1-2.5 % strain associated with steel reinforcement yield. This is critical for crack control when rebar yields at SLS.
- The amorphous fiber mix, by contrast, localized at just 1.4 %, revealing greater brittle behavior.
In deep beam tests, the reference mix reached a peak bending stress of 16.78 MPa, the amorphous fiber mix 19.04 MPa, and the CEM III-based mix 20.19 MPa.
Thin beams, which benefited from improved fiber alignment due to the casting direction, exhibited higher strengths between 21 and 25 MPa. This alignment effect was especially pronounced in the steel fiber mixes.
The steel-reinforced concretes also developed denser crack patterns with smaller spacing, and under cyclic loading, they retained stiffness.
Conversely, the amorphous fiber mix showed wider crack spacing and a noticeable decline in stiffness with increased deflection.
The reduced ductility in this mix was attributed to a stiffer bond-slip interface, a hydrophobic fiber surface, as well as a higher likelihood of fiber rupture at the crack plane.
Durability Despite Harsh Conditions
To assess long-term performance, thin beams were submerged for six months in either geothermal or tap water.
The amorphous fiber mix demonstrated impressive corrosion resistance, increasing by 9 % in flexural strength after immersion in geothermal water.
The steel fiber mixes, however, lost 11 to 23 % in strength under the same conditions, possibly due to degradation of the fiber-matrix bond from surface corrosion.
Despite the reduction in strength, the steel fiber mixes retained their pre-exposure advantages in strain capacity and crack control.
This makes them well-suited to structural applications where ductility and crack limitation are critical to long-term performance.
Design Implications and Future Directions
The study highlights the importance of selecting a fiber type and cement composition that match the structural and environmental demands.
CEM III was the most sustainable alternative to CEM I, but this sustainability didn't sacrifice mechanical performance (when combined with steel fibers).
The inverse analysis and hinge model simulations proved to be effective tools for characterizing and predicting tensile performance.
These findings will also support the next phase of the ReSHEALience project, which involves validating the materials in full-scale demonstrators such as geothermal water tanks.
Journal Reference
Lo Monte, F., et al. (2025). Tensile characterization of high-performance fibre-reinforced concrete: effect of steel or amorphous metallic fibres and of cement type. Mater Struct 58, 331. DOI: 10.1617/s11527-025-02825-4
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