Why Aggregates Larger Than 5mm Are Not Recommended for UHPC: Analysis of Technical Principles and Performance Impact

The micro determines the macro: a fraction of a millimeter in aggregate particle size creates a world of difference in UHPC performance.

In the material world of ultra-high performance concrete (UHPC), the selection of every component is like the meshing of precision gears, and controlling the aggregate particle size is the key variable that determines its performance ceiling. As an industry player with 28 years of dedicated experience in the UHPC/GRC/GRG/GRP materials field, Qinglong Group has always strictly kept the aggregate particle size below 5mm when undertaking benchmark projects such as the light-transmitting concrete project at Century Plaza on Nanjing East Road and the special-shaped components for the Dongguan Women and Children's Activity Center. Behind this technical detail lies a deep integration of materials science and engineering practice.

1. The Underlying Technical Logic of UHPC Aggregate Particle Size Limits

The reason UHPC can achieve outstanding performance with compressive strength exceeding 150MPa and an elastic modulus of 40GPa lies in its “dense solid” microstructure. When the aggregate particle size exceeds 5mm, it directly damages the interfacial transition zone between the cementitious material and the fibers—this zone is like the “Achilles' heel” of concrete. Oversized aggregate particles lead to more interfacial defects, making it difficult for steel fibers to fully exert their bridging effect. Through electron microscope scanning, the Qinglong R&D Center found that the fiber-to-matrix bond strength of UHPC specimens using 3-5mm continuously graded aggregates was 37% higher than that of specimens with 8mm aggregates—this is precisely the scientific basis for strict particle size control.

2. The Chain Effects of Aggregates Over 5mm on Key UHPC Properties

In actual engineering, the impact of oversized aggregate particles is systematic. First is the deterioration of workability: large aggregate particles significantly increase the viscosity of the mix, causing insufficient flow and trapped air bubbles when casting intricately shaped GRC components. Second is reduced durability: comparative tests on a municipal project showed that the impermeability grade of UHPC using 6mm aggregates dropped from P20 to P12, and the carbonation depth increased 2.3-fold. Even more critical is the decline in mechanical performance: the General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC), which Qinglong participated in drafting, clearly stipulates that when the maximum aggregate particle size exceeds 5mm, the flexural toughness index will fail to meet the C120 class requirements.

3. Particle Size Control in Qinglong's Full-Chain Solutions

As a national high-tech enterprise, Qinglong has established a full-process quality control system running from mine aggregate screening to finished product testing. At its production base in Nanning, Guangxi, German-imported air classifier screening equipment is used to strictly control the aggregate grading, ensuring that 0-5mm particles account for more than 98%. Thanks to this refined control, Qinglong's UHPC products, applied in the double-curved curtain wall panels of a landmark building in Shenzhen, achieved the breakthrough of 3.8-meter-span components weighing only 85kg/m², a 60% weight reduction compared with traditional stone curtain walls. Meanwhile, nano-scale mineral admixture technology jointly developed with South China University of Technology compensates for the early-age strength loss caused by fine aggregates, enabling the products to reach 90% of the design strength at 7 days.

From the microscopic perspective of materials science to the macroscopic practice of engineering applications, the restriction on UHPC aggregate particle size is by no means a technical dogma, but the optimal solution balancing performance and cost. Qinglong Group's 28 years of accumulated industry experience prove that only by deeply coupling material properties with engineering requirements can UHPC reveal its unique value in high-end buildings such as grand theaters and commercial complexes. In the future, with the implementation of standards such as Ultra-High Performance Concrete (UHPC) Exterior Wall Panels, aggregate control technology will become a core indicator of a UHPC manufacturer's professionalism, and Qinglong will continue to push the technical boundaries of new architectural decoration materials with a meticulous and excellence-driven attitude.