When Selecting Fibers for UHPC, How to Choose Between Metal Fibers and Non-Metal Fibers?

Fibers are the core component enabling UHPC to achieve high toughness and crack resistance. The choice between metallic and non-metallic fibers directly affects the material's mechanical properties, durability, and suitability for specific applications. As an enterprise with 28 years of experience in UHPC R&D and application, Qinglong Group has summarized scientific fiber selection principles based on practical data from thousands of projects, helping customers precisely match project requirements.

Metallic fibers: mechanical performance first, suited to high-toughness and load-bearing scenarios. Metallic fibers are represented by copper-plated micro steel fibers, whose core advantages are high strength, high elastic modulus, and excellent interfacial bonding, significantly improving the flexural strength, fracture energy, and impact resistance of UHPC. The copper-plated steel fibers selected by Qinglong Group have a diameter of 0.1-0.2mm, a length of 6-12mm, and an aspect ratio of 50-100; at a dosage of 3%-5% (by volume), they can raise the flexural strength of UHPC to 25-35MPa and the fracture energy to ≥20kJ/m², far exceeding non-metallic fibers. These fibers are suitable for scenarios with high demands on toughness and impact resistance, such as load-bearing components of large public buildings, bridge structures, and sculptures. In the Shanghai Astronomy Museum public art project, the use of steel fibers gave UHPC sculptures over 3 meters tall sufficient deformation resistance to withstand external impact during transportation and installation; in load-bearing curtain wall components of high-rise buildings, steel fibers improved the components' resistance to wind loads and seismic forces. However, metallic fibers have limitations: once the copper plating wears away, they are prone to rusting and are unsuitable for corrosive environments with high humidity or high salt spray; their high density (about 7.8g/cm³) increases the self-weight of components; and their cost is relatively high, about 3-5 times that of non-metallic fibers.

Non-metallic fibers: durability first, suited to corrosion-resistant and lightweight scenarios. Non-metallic fibers mainly include polypropylene fibers, polyethylene fibers, and glass fibers. Their core advantages are light weight, corrosion resistance, aging resistance, and relatively low cost. The polypropylene fibers commonly used by Qinglong Group have a diameter of 20-50μm and a length of 6-12mm; at a dosage of 2%-3%, although the flexural strength (15-20MPa) and fracture energy (5-10kJ/m²) are lower than those of metallic fibers, they can effectively suppress early shrinkage cracking of UHPC and improve impermeability and frost resistance. These fibers are suitable for scenarios such as outdoor highly corrosive environments (seaside, humid areas), weight-sensitive components, and non-load-bearing decorative components. In the exterior facade perforated panel project of the Ouargla Hotel in Algeria, the use of polypropylene fibers kept the components free of rust and cracking after years of use in a humid environment; in the white GRC cladding panel project of Qiangwei Garden in Zengcheng, Guangzhou, the lightweight nature of non-metallic fibers reduced building loads while providing good weathering resistance. Limitations of non-metallic fibers: limited improvement in mechanical performance, unable to meet high-toughness or load-bearing requirements; they soften easily at high temperatures (>100°C) and are unsuitable for high-temperature conditions.

Core decision dimensions for fiber selection: scenario fit and performance balance. Qinglong Group has summarized three major selection principles. First, decide by mechanical requirements: for projects with clear requirements on toughness, impact resistance, and load-bearing capacity (e.g., bridges, large sculptures, load-bearing curtain walls), metallic fibers are preferred; for those that only need shrinkage crack suppression and basic crack resistance (e.g., decorative components, outdoor landscaping), non-metallic fibers can be chosen. Second, decide by environmental conditions: in environments with high salt spray, high humidity, or corrosive gases (e.g., seaside buildings, chemical park projects), corrosion-resistant non-metallic fibers such as polypropylene are preferred; in dry, non-corrosive environments, metallic fibers can be selected according to mechanical requirements. Third, decide by cost and self-weight: where budgets are limited or self-weight is a concern (e.g., decorative components on high-rise buildings), non-metallic fibers offer greater advantages; where budgets are ample and ultimate mechanical performance is pursued, metallic fibers can be chosen. In addition, Qinglong also offers hybrid fiber solutions, such as steel fiber + polypropylene fiber (ratio 2:1), which achieved a balance between mechanical performance and corrosion resistance in a municipal bridge project.

Supporting technical guarantees for fiber selection: Qinglong's customization and quality control. Fiber performance depends on compatibility with other components. Qinglong Group's provincial-level R&D center optimizes cementitious material mix proportions and admixture selection according to fiber type—for example, adjusting superplasticizer dosage to improve fiber dispersion in metallic fiber applications, and optimizing particle grading to enhance interfacial bonding in non-metallic fiber applications. Meanwhile, automated mixing equipment ensures uniform fiber dispersion and prevents agglomeration. In the Century Plaza project on Nanjing East Road in Shanghai, the uniform distribution of steel fibers kept the toughness uniformity of light-transmitting concrete components within ≤±5%. In addition, Qinglong provides fiber performance test reports and project-specific recommendations to help customers make informed choices and avoid blind selection.

The essence of fiber selection for UHPC is balancing scenario requirements against performance and cost. Neither metallic nor non-metallic fibers are absolutely superior—the key lies in precise matching. With extensive project experience and professional R&D capabilities, Qinglong Group provides customers with customized fiber solutions to ensure that the performance advantages of UHPC are fully realized. Customers are advised to make scientific decisions based on mechanical requirements, environmental conditions, and budget, under the guidance of professional manufacturers.