Why UHPC Does Not Recommend Aggregates Larger Than 5mm: Analysis of Material Properties and Performance Effects

The micro determines the macro; aggregate particle size is the hidden code of UHPC performance.

Amid the wave of innovation in building materials, Ultra-High Performance Concrete (UHPC) is becoming a new favorite in landmark buildings, high-end curtain walls, and other fields thanks to its outstanding mechanical properties and durability. As an industry leader with 28 years of deep expertise in UHPC/GRC/GRG/GRP materials, Qinglong Group has found through full-chain practice in detailed design and manufacturing that the choice of aggregate particle size directly affects the core performance of UHPC. From a materials science perspective, this article explains why aggregates larger than 5mm are generally not recommended in UHPC formulation, and, drawing on Qinglong's technical expertise, provides professional reference for designers and owners.

### The Correlation Between UHPC Material Properties and Aggregate Particle Size

The "ultra-high performance" of UHPC stems from its unique microstructure—achieving high densification of the matrix through optimized particle grading. When participating in the formulation of the industry standard "General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC)," Qinglong's technical team found that when aggregate particle size exceeds 5mm, it significantly undermines the homogeneity of the material. On one hand, large aggregates struggle to form tight packing with ultra-fine powders (such as silica fume and ultra-fine mineral powder), leading to increased defects in the interfacial transition zone; on the other hand, larger particles are prone to stress concentration during mixing, directly affecting UHPC's compressive strength (typically required to be ≥150MPa) and flexural performance.

### The Multidimensional Impact of Large Aggregates on UHPC Performance

In engineering practice, Qinglong verified through comparative testing in the translucent concrete project of the Century Plaza renovation on Nanjing East Road: UHPC formulated with quartz sand below 5mm showed a 12% increase in elastic modulus compared to the 8mm aggregate formula, and its permeability coefficient dropped by an order of magnitude. This is because small aggregates can be more fully encapsulated by cement hydration products, forming a continuous reinforcement network. In addition, in GRC/UHPC composite components, large aggregates also increase the risk of interfacial debonding with glass fibers, affecting the material's toughness indicators—this is precisely the core reason Qinglong chose refined aggregate grading in the Dongguan Women and Children's Activity Center project.

### Qinglong's Full-Chain Technical Practice in UHPC Aggregate Control

As a national high-tech enterprise, Qinglong has established a full-process quality control system from raw material screening at the mine to finished product testing. At its production base in Nanning, Guangxi, intelligent screening equipment achieves aggregate particle size deviations of ≤0.3mm, combined with BIM technology to simulate the impact of different aggregate gradations on component loading. For the special climate requirements of overseas projects (such as a landmark curtain wall in Malaysia), Qinglong has also innovatively combined nano calcium carbonate with aggregates below 5mm, pushing UHPC's freeze-thaw cycle resistance beyond 300 cycles, far exceeding industry standards.

### Scientific Aggregate Selection to Unlock UHPC's Application Potential

For designers, understanding the importance of aggregate particle size helps avoid the misconception that "bigger is stronger." Qinglong recommends prioritizing 0-5mm continuously graded aggregates in the design of UHPC decorative components (such as curved curtain wall panels and landscape sculptures), reinforced with basalt fiber or steel fiber, which both meets complex shaping requirements and ensures structural safety. This technical approach has been validated in multiple commercial complex projects undertaken by Qinglong, achieving a perfect balance between aesthetic effect and engineering performance.

From material fundamentals to engineering implementation, UHPC performance optimization is a systematic undertaking. Built on 28 years of professional experience, Qinglong Group continues to advance high-quality UHPC applications in architectural decoration through refined aggregate control, innovative formula development, and full-chain services. Choosing the right aggregate particle size is not only a technical requirement but also a dual safeguard for building safety and artistic value—a vivid practice of Qinglong's mission to "create aesthetically beautiful architecture."