A full-scale laboratory study conducted by the Norwegian University of Science and Technology (NTNU) confirms that ReforceTech MiniBars™ work effectively as shear reinforcement in concrete beams — and that existing design standards can be applied directly.
Background: Why shear matters
When concrete structures fail in shear, they often do so suddenly. Unlike bending failure, which typically gives visible warning through gradual deflection, shear failure can be rapid and brittle. This makes shear capacity a critical design parameter — particularly for beams without traditional stirrup reinforcement.
Conventional shear reinforcement relies on steel stirrups, which add complexity to the reinforcement process, require corrosion protection, and contribute to the overall material footprint of a structure. Fiber reinforcement has long been explored as an alternative, but documentation has primarily existed for steel fibers. The question for basalt fiber-based products like MiniBars™ has been: does the documentation hold up under rigorous structural testing?
The NTNU study, published in September 2024, provides a clear answer.
The study: 15 full-scale beams, two universities
The research program was carried out jointly by NTNU’s Department of Structural Engineering in Trondheim and the Department of Manufacturing and Civil Engineering in Gjøvik. Fifteen full-scale concrete beams were cast and tested to shear failure under four-point bending.
The test program included two beam geometries: nine regular beams (150 × 250 mm cross section) and six shallow beams (360 × 180 mm cross section), all with a length of 2850 mm. Beams were produced with three different MiniBars™ dosages: 0, 10, and 20 kg/m³. All beams were designed without traditional shear reinforcement in the test zone, making MiniBars™ the sole source of shear capacity in the fiber-reinforced series.
Concrete quality was B35, and the MiniBars™ used were generation 3, type 43mm length — the standard commercial product from ReforceTech.
Results: Significant capacity increase at low dosage
The test results were clear and consistent across all three beams in each series.
For regular beams, adding 10 kg/m³ of MiniBars™ increased average shear capacity from 92.4 kN to 156.3 kN — a 70% increase. Increasing the dosage further to 20 kg/m³ gave only a marginal additional improvement (167.7 kN), indicating that 10 kg/m³ represents an efficient and practical dosage for structural shear applications.
For shallow beams, a 17% increase in shear capacity was documented with 10 kg/m³ MiniBars™. The lower relative improvement is consistent with findings in the literature for wide, shallow beam geometries, which are inherently less susceptible to shear failure due to their geometry.
Beyond peak load, the results revealed something equally important for structural performance: fundamentally different failure behavior.
A different kind of failure — and why it matters
In the reference beams without MiniBars™, the first diagonal crack led rapidly to final shear failure. The structure had no mechanism to redistribute load once cracking initiated.
In the beams with MiniBars™, the behavior was markedly different. When the first diagonal crack developed, multiple parallel cracks formed in the shear zone. Load continued to increase significantly before final failure occurred. This behavior — documented through Digital Image Correlation (DIC) photography — demonstrates that MiniBars™ do not simply add strength. They change the way the structure behaves: slowing crack propagation, redistributing internal forces, and substantially increasing energy absorption.
This transition from brittle to more ductile behavior has practical significance beyond the numbers. It means that structures reinforced with MiniBars™ give more warning before failure and have greater capacity to absorb unexpected loads.
Design verification: NB38 and new Eurocode 2
A central objective of the study was to verify whether existing design standards for steel fiber concrete — NB38 (Norwegian Concrete Association Publication No. 38) and Annex L of the forthcoming Eurocode 2 revision (FprEC2:2022) — can be used to calculate shear capacity when MiniBars™ are used instead of steel fibers.
The answer is yes.
Calculated shear capacities using characteristic material values and a material factor of 1.0 were compared against experimental results across all beam types. In every case, the experimental values exceeded the calculated values, confirming that the design formulas provide results on the conservative side.
Safety margins ranged from 1.33 for regular beams with 10 kg/m³ to 1.93 for shallow beams — all well above 1.0. NB38 has already been updated to align with the FprEC2:2022 formulas, and the Norwegian Concrete Association’s publication explicitly opens for the use of other fiber types when performance can be documented. This study provides that documentation.
In practical terms: engineers and designers working with NB38 or the new Eurocode 2 can apply the same calculation methodology for MiniBars™ that they already use for steel fiber concrete.
A peer-reviewed study published in Composite Structures (Lin et al., 2025) further validates these findings against four international design codes, including ACI 318-19, confirming conservative safety margins across all frameworks.
What this means for design and specification
The study confirms three things that are directly relevant for structural engineers considering MiniBars™:
MiniBars™ can replace traditional stirrups as shear reinforcement in concrete beams and slabs. The performance has been verified at full scale under standardized test conditions.
The 10 kg/m³ dosage delivers the majority of the available shear improvement. Going to 20 kg/m³ adds marginal benefit and may introduce workability challenges due to fiber balling at higher dosages with coarse aggregate.
Existing design methods apply. No new calculation framework is required. Engineers can work within the established NB38 and Eurocode 2 methodology.
About MiniBars™
MiniBars™ are high-performance composite macrofibers made from basalt fiber reinforced polymer wires. They are non-corrosive, have a specific gravity close to that of concrete for uniform dispersion, and offer high tensile strength exceeding 1400 MPa. They are manufactured under ISO 9001 quality management and are designed for use in structural concrete applications including beams, slabs, wall panels, tunnel segments, and marine structures.
Download the full report
The complete NTNU report — Shear Capacity of Concrete Beams Reinforced with High Performance Composite Fibers (Minibars) from ReforceTech AS — is available for download below.
The findings have also been published in the international journal Composite Structures (Lin et al., 2025).
For technical inquiries, contact ReforceTech directly.