Experimental Investigation of RCC Beams Using a Layer of Ultra-High-Performance Reinforced Concrete with different Types of Steel Fibers for Beam Strengthening Applications

Abstract

Concrete, one of the most widely used construction materials globally, offers versatility, strength, and cost-effectiveness. However, conventional concrete is inherently brittle, possesses low tensile strength, and is prone to cracking and environmental deterioration, which limits its long-term durability. To overcome these shortcomings, Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) has emerged as an advanced cementitious composite that exhibits superior mechanical performance, enhanced ductility, and exceptional durability. UHPFRC is characterized by its ultra-high compressive strength, typically exceeding 120 MPa. Its exceptional performance is achieved through optimized particle packing, a very low water-to-binder ratio (0.18–0.22), and the incorporation of high-strength steel or synthetic fibers (1–3% by volume). The design of UHPFRC eliminates coarse aggregates and relies on fine materials such as cement, silica fume, quartz sand, and high-range water-reducing admixtures to produce a dense, homogeneous microstructure. The inclusion of fibers imparts crack-bridging capability and pseudo-ductile behavior to UHPFRC, allowing it to sustain significant tensile deformation after cracking. This leads to remarkable improvements in impact resistance, fatigue performance, and energy absorption capacity. Consequently, UHPFRC is ideal for structures subjected to dynamic loads, blast effects, or severe exposure environments. Its modulus of elasticity typically ranges from 45 to 55 GPa, and its fracture energy is several times greater than that of conventional or high-performance concrete. Applications of UHPFRC extend across various sectors including bridges, high-rise buildings, tunnels, and precast components. It is also widely used for strengthening and rehabilitation of existing structures, offering enhanced bond strength and durability without adding significant weight. Although UHPFRC involves higher initial costs and stringent mixing and curing requirements, its superior strength, durability, and low maintenance needs make it a sustainable solution. Representing a significant advancement in concrete technology, UHPFRC provides an integrated solution to strength, ductility, and durability challenges—ushering in a new era of resilient and long-lasting infrastructure.

Introduction

Concrete has long been a fundamental construction material due to its strength, versatility, and affordability. However, conventional concrete suffers from low tensile strength, brittleness, and poor durability, leading to cracking and high maintenance costs. To overcome these limitations, Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) has emerged as a next-generation material offering exceptional strength, ductility, and durability.

UHPFRC achieves compressive strengths above 120 MPa through a refined mix design that eliminates coarse aggregates and incorporates fine materials like silica fume, quartz sand, and GGBS, resulting in a dense, low-permeability matrix. The addition of 1–3% steel or synthetic fibers provides crack-bridging capacity, transforming the material from brittle to pseudo-ductile. Despite higher initial costs, UHPFRC’s longevity and reduced maintenance make it a sustainable solution for bridges, high-rise buildings, marine structures, and retrofitting applications.

Aim

To evaluate the mechanical and structural performance of UHPFRC incorporating silica fume and Ground Granulated Blast Furnace Slag (GGBS) with varying types and volume fractions of steel fibers, and to assess its effectiveness as a strengthening layer for reinforced concrete (RC) beams.

Objectives

• Compare UHPFRC mixes with silica fume and GGBS using 1.0% and 1.5% steel fiber volumes.

• Conduct compression, flexural, and impact tests to assess strength, toughness, and crack resistance.

• Evaluate the performance of UHPFRC as a bottom strengthening layer in RC beams to improve flexural capacity, stiffness, and energy absorption.

Literature Review

Previous research confirms UHPFRC’s superior mechanical strength, ductility, and durability:

• Studies by Li, Chun, Xing, Abu Bakar, Ma, Zhou, Yoo, Ahn, and Yu demonstrated that UHPFRC enhances flexural capacity, impact resistance, ductility, and corrosion resistance compared to normal and high-performance concrete.

• Applications include beam strengthening, column jacketing, hybrid reinforcement systems (CFRP + steel), and bridge construction, all showing significant structural improvement.

Methodology

The experimental program used OPC (53 grade) with silica fume, GGBS, quartz sand, and steel fibers (straight, hooked, twisted) in varying proportions (0.5–2%).
Specimens included cubes, cylinders, and RC beams for compressive, tensile, flexural, and impact testing.
All mixes maintained a low water-to-binder ratio (0.18–0.22) and were cured for 28 days.
Results were compared with control M40 concrete to evaluate performance gains and optimal fiber content.

Results and Discussion

• Workability: Maintained high flowability (slump 124–130 mm) due to superplasticizer use, ensuring uniform fiber distribution.

• Compressive Strength: Increased over 200%, with maximum value 159.8 MPa (1% long twisted fibers). Beyond 1%, strength decreased slightly due to fiber clustering.

• Split Tensile Strength: Improved from 3.72 MPa (control) to 8.21 MPa with 1.5% long twisted fibers—a 120% increase.

• Flexural Strength: RC beams strengthened with a 40 mm UHPFRC layer showed dramatic improvement—from 6.2 MPa (control) to 37.4 MPa (LT1), a six-fold rise. Long-twisted fibers produced the best ductility and post-crack toughness.

• Impact Resistance: Peak load increased from 310.8 kN (control) to 332.4 kN (LT1.5), showing greater energy absorption and crack resistance without loss of ductility.

Conclusion

The experimental study evaluated the mechanical behavior of reinforced concrete beams strengthened with a 40 mm UHPFRC layer incorporating different steel fiber types (short straight, long straight, and long twisted) and volume fractions (1% and 1.5%). Tests on compressive, split tensile, flexural strength, and impact performance revealed that the inclusion of steel fibers significantly enhanced strength, ductility, and post-cracking behavior.The long twisted fibers (LT) achieved the best overall performance due to superior anchorage and crack-bridging ability. Optimum results were obtained at 1% fiber content, as higher volumes slightly reduced workability and caused fiber clustering. The LT1.5 mix recorded the highest peak load (332.4 kN) with stable deflection, confirming improved load capacity without loss of ductility. Overall, the UHPFRC layer effectively improved the flexural and impact resistance of RC beams, demonstrating its suitability for structural strengthening and retrofitting applications.

References

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Copyright

Copyright © 2025 Dr. S. S. Angalekar, Mr. S. N. Ramteke, Miss. Rutuja S. Kanherkar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.