A new study shows that reinforced concrete beams built with U-shaped engineered cementitious composite (ECC) and hybrid steel–GFRP reinforcement offer significantly better ductility and deflection performance than conventional designs.
Study: Serviceability and ductility behaviour of hybrid reinforced concrete beams partially composed of engineered cementitious composite (ECC). Image Credit: Evgenii Bakhchev/Shutterstock.com
Published in Scientific Reports, the research explores how different ECC configurations and reinforcement types affect the structural behavior of RC beams. It compares these hybrid systems to traditional concrete beams and focuses on two key ECC setups: a tension layer of varying thickness and a U-shaped formwork.
Background
Corrosion of steel reinforcement remains one of the most persistent durability challenges for reinforced concrete—particularly in aggressive environments like underground tunnels, coastal regions, and bridge foundations. One widely studied solution is replacing steel bars with glass-fiber-reinforced polymer (GFRP) bars, which are non-corrosive, chemically resistant, and require less concrete cover.
GFRP bars offer several long-term advantages: they extend maintenance intervals, reduce environmental impact, and are non-toxic. However, their lack of ductility compared to steel makes them less ideal on their own. To address this, researchers have been investigating hybrid reinforcement systems that combine steel and GFRP with advanced materials like ECC, which is known for its strain-hardening behavior and tight crack control.
Despite growing interest, there’s still limited research on combining steel–GFRP reinforcement with ECC in concrete beams, especially when using U-shaped ECC configurations. This study takes a closer look at how these combinations impact serviceability and ductility.
Methods
Seven RC beams were cast with partial ECC and hybrid reinforcement, each with the same cross-section of 200 × 300 mm. The beams were divided into two groups:
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Group 1: GFRP-RC beams where part of the GFRP was replaced with steel bars.
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Group 2: Beams featuring ECC in the tension zone—either as a flat bottom layer of varying thickness (50, 100, and 150 mm) or as a U-shaped formwork with the same ECC volume.
The beams were cast using wooden molds fitted with U-shaped reinforcement cages. Four-point bending tests were carried out to evaluate deflection and ductility under load. Strain gauges were attached to both steel and GFRP bars to monitor tensile strain, with an additional gauge at midspan for compressive strain. Deflection was tracked using LVDTs placed at key positions, and all load and displacement data were logged through an automated data acquisition system.
Results and Discussion
Beams reinforced solely with GFRP showed brittle failure once the concrete reached its maximum strength. In contrast, hybrid-reinforced beams exhibited ductile behavior beyond the concrete’s ultimate limit, absorbing more energy and maintaining structural integrity longer.
Among the ECC configurations, the U-shaped formwork delivered the best overall performance. Compared to an equally volumed flat layer, it improved post-cracking stiffness, ultimate load capacity, shear transfer across the interface, and ductility index. The U-shape also helped maintain bond strength at the interface, allowing the beam to act as a more unified structural element through failure.
Increasing the thickness of the ECC tension layer reduced initial stiffness but led to more vertical cracks, higher deflections, and improved energy absorption in both elastic and post-yield phases. Thicker ECC also allowed for better yielding behavior under load.
When experimental deflection results were compared with predictions from structural design codes, both ACI 318-19 and CSA S806-12 aligned well with observed data. However, ACI 440.1R-15 significantly underestimated deflections. Yoon’s model, based on Bischoff’s method, proved more reliable in capturing deflection behavior after yielding, especially in hybrid-reinforced beams.
Conclusion
This study provides clear evidence that integrating ECC and hybrid reinforcement into RC beams improves both ductility and serviceability, especially when ECC is applied in a U-shaped configuration. Key performance indicators like crack distribution, load-strain behavior, and moment-curvature response all point to stronger, more durable structural behavior.
Beyond performance gains, the findings offer practical insights for construction. U-shaped ECC elements could be precast and filled on-site with standard concrete or grout, streamlining construction in corrosive or hard-to-access environments. Alternatively, ECC tension layers of optimal thickness could serve as permanent formwork, eliminating the need for full-length bottom shuttering and reducing construction time and cost.
Overall, this research supports the use of hybrid ECC systems in infrastructure projects where long-term durability and reduced maintenance are critical, such as coastal bridges, marine structures, or chemically exposed foundations.
Journal Reference
Radwan, A. A., Ghallab, A., & Maree, A. M. F. (2025). Serviceability and ductility behaviour of hybrid reinforced concrete beams partially composed of engineered cementitious composite (ECC). Scientific Reports, 15(1). DOI: 10.1038/s41598-025-15779-y. https://www.nature.com/articles/s41598-025-15779-y
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