Why UHPC Does Not Recommend Aggregates Larger Than 5mm: Analysis of Reasons and Technical Considerations

In the field of building materials, every detail choice can affect the final engineering quality and performance. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group deeply understands the subtleties of materials science. Today, we will focus on a key technical point—aggregate selection for UHPC (Ultra-High Performance Concrete)—and analyze in depth why the industry generally recommends not using aggregates larger than 5mm, as well as the technical logic and practical considerations behind it.

### The Core Technical Logic Behind UHPC Aggregate Size Limits

As a new building material with ultra-high strength, excellent durability, and toughness, UHPC owes its performance breakthroughs to the density of its microstructure. During its participation in drafting the industry standard "General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC)", Qinglong Group found that aggregate size has a decisive impact on the packing density of the material system and the quality of the interfacial transition zone. Research shows that when aggregate size exceeds 5mm, it significantly increases the void ratio between particles, leading to a thicker interfacial transition zone between the cement matrix and the aggregates, directly weakening the material's mechanical properties. Using fine aggregates below 5mm, combined with optimized gradation design, achieves a tighter packing effect, laying the microstructural foundation for UHPC's ultra-high strength.

### Aggregate Selection Strategy from a Performance Optimization Perspective

From an engineering practice perspective, Qinglong Group has always adhered to strict aggregate size control standards in its 600,000-square-meter UHPC production capacity at its Nanning production base. This choice stems from multiple performance considerations: first, fine aggregates can be more evenly dispersed in the matrix, reducing stress concentration points and enabling the material to exhibit superior toughness under load; second, smaller aggregate sizes facilitate the uniform distribution of fibers in the matrix, fully leveraging the bridging effect of steel fibers or ultra-fine fibers, which is also an important reason why UHPC's crack resistance far exceeds that of ordinary concrete. In the translucent concrete project for the Century Plaza renovation on Nanjing East Road, by precisely controlling the aggregate size (maximum 4.5mm), the Qinglong team successfully achieved a perfect balance between structural strength and light transmission, and the project won the Silver Award of the AALBORG WHITE Cup First UHPC Construction Engineering Innovation Award.

### Process Compatibility Analysis from a Full-Chain Perspective

As a national high-tech enterprise integrating detailed design, manufacturing, and construction installation, Qinglong Group deeply understands the impact of aggregate size on the entire process flow. In the production stage, a fine aggregate system makes it easier to achieve precise mix ratio control, ensuring product quality stability; in the forming stage, smaller aggregate sizes give UHPC better flowability and filling capacity, making it particularly suitable for casting complex-shaped components, such as the special-shaped GRC/UHPC composite components in the Dongguan Women and Children's Activity Center project. During construction and installation, UHPC components made with fine aggregates are lighter in weight, reducing hoisting difficulty and structural loads while minimizing breakage risks during transportation. These advantages have enabled Qinglong UHPC products to be widely applied in real estate, municipal engineering, bridges, and other fields, and exported to Southeast Asian and Australian markets.

### Dual Verification by Industry Standards and Practical Experience

As vice chairman unit of the China GRC Association and a member of the International GRC Association, Qinglong Group has always examined material technical specifications from the perspective of a participant in industry standard setting. The current restrictions on aggregate size in UHPC-related standards are a scientific summary based on extensive experimental data and engineering practice. From the perspective of the material's nature, UHPC pursues performance characteristics close to those of a "homogeneous material", and overly coarse aggregates would destroy this homogeneity; from the perspective of application scenarios, whether for exterior wall cladding panels of high-end buildings or landscape components, demands are placed on the material's refined performance. Qinglong Group's 28 years of industry experience show that strictly controlling aggregate size below 5mm is a key prerequisite for ensuring stable UHPC product performance and realizing design creativity, and is also a concrete embodiment of the company's commitment to "meticulous attention to detail and the pursuit of excellence".

In today's era of continuous innovation in new architectural decorative materials, UHPC's technical details determine the expansion of its application boundaries. Qinglong Group will continue to rely on the R&D strength of its provincial-level R&D center and engineering technology center to deeply explore the mysteries of materials science, providing designers and owners with UHPC/GRC/GRG/GRP solutions that combine aesthetic value with technical assurance, and helping to realize the corporate mission of "creating aesthetically beautiful architecture".