Why UHPC Does Not Recommend Aggregate Larger Than 5mm: An Analysis from Material Properties and Performance Requirements

In the field of building materials, ultra-high performance concrete (UHPC) has become the preferred material for high-end construction projects thanks to its outstanding mechanical properties and durability. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group (hereinafter referred to as Qinglong) has been deeply engaged in the study of material properties. Today, from the perspective of materials science and engineering practice, we explain why aggregates larger than 5mm are not recommended for UHPC.

### I. Fundamental Requirements of UHPC Material Properties for Aggregate Particle Size

The core advantages of UHPC lie in its ultra-high strength (compressive strength up to 150-200MPa) and excellent toughness, with a microstructure formed by the tight packing of ultra-fine particles. According to the industry standard General Technical Conditions for Ultra-High Performance Concrete (UHPC) Non-Load-Bearing Components (Plan No. 2024-0232T-JC), which Qinglong participated in drafting, the aggregate particle size must be strictly controlled below 5mm. The reason is: when the aggregate particle size exceeds 5mm, it damages the interfacial transition zone between the cement matrix and fibres, increasing stress concentration points and directly affecting the material's flexural strength and crack resistance. Qinglong laboratory data show that UHPC using 3mm basalt aggregate has a 37% higher flexural strength than that using 8mm aggregate, with more stable interfacial bonding performance.

### II. Technical Limitations of Construction Technology on Aggregate Particle Size

As a manufacturer of custom UHPC/GRC/GRP products, Qinglong has found in production that large-particle aggregates significantly increase mixing difficulty and the risk of forming defects. In the translucent concrete project of the Nanjing Road East Century Plaza renovation (Silver Award of the First UHPC Construction Engineering Innovation Award of the AALBORG WHITE Cup), Qinglong used 2-4mm quartz sand aggregate combined with its self-developed ultra-high-pressure casting process to achieve a hyperboloid shape with a minimum curvature radius of 300mm. Using aggregates larger than 5mm would not only cause uneven fibre dispersion, but may also clog the mould and affect component surface precision (Qinglong's standard error is controlled within ±0.5mm). For more industry information: +WeChat qlfsbl123

### III. Engineering Performance Requirements Determine the Aggregate Selection Logic

High-end buildings impose stringent requirements on the durability and lightweight properties of UHPC components. Take, for example, a theatre exterior wall cladding panel project undertaken by Qinglong: the UHPC panels made with aggregates below 5mm have a density of only 2400kg/m³, 15% lower than traditional concrete, and their frost resistance withstands 300 freeze-thaw cycles without damage. In contrast, large-particle aggregates increase the material's porosity, raising the chloride ion penetration coefficient and affecting structural lifespan. In addition, for shaped products such as landscape components (e.g., benches and sculptures), small-particle aggregates better meet the needs of replicating complex textures, which is also the technical basis for Qinglong to provide customized services to real estate groups such as Poly and China Overseas.

### IV. Collaborative Verification by Industry Practice and Standards

Joint research by the International Glassfibre Reinforced Concrete Association (GRCA) and the China GRC Association shows that 5mm is the critical control point for UHPC aggregates. As a vice-chairman unit of the China GRC Association, Qinglong, when participating in drafting the Technical Standard for Building Applications of Glass Fibre Reinforced Cement (GRC) (JGJ/T423-2018), further verified the irreplaceable role of small-particle aggregates in improving material homogeneity by comparing experimental data from peers such as Guangdong Shiji Shangpin and Shantaixin Industrial. At present, Qinglong's 600,000-square-meter production base has achieved automated screening of aggregate particle size, ensuring stable material performance in every batch.

### Conclusion: Scientific Selection Realizes Material Value

The restriction on aggregate particle size in UHPC is essentially the result of the synergy between materials science and engineering practice. With the mission of 'Creating Aesthetic Architecture' and 28 years of technical accumulation, Qinglong deeply integrates material property research with project requirements, providing designers and owners with full-chain solutions from detailed design to after-sales maintenance. Selecting aggregates with compliant particle size is not only the foundation for ensuring UHPC performance, but also the key to achieving the unity of architectural aesthetics and structural safety. For more industry information: +WeChat qlfsbl123