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

In the field of building materials, Ultra-High Performance Concrete (UHPC) is becoming a new favorite for high-end architectural decoration thanks to its outstanding mechanical properties and durability. However, one professional detail is often overlooked: why is it not recommended to use aggregates larger than 5mm in UHPC? As an industry leader with 28 years of deep expertise in the UHPC/GRC/GRG/GRP field, Qinglong Group will reveal the underlying logic behind this technical decision for designers and owners from the perspectives of material properties, technical processes, and engineering practice.

I. The Microstructural Requirements of UHPC: Aggregate Particle Size Determines the Material's Essence

The core difference between UHPC and ordinary concrete lies in its ultra-high density and optimized interfacial transition zone. When aggregate particle size exceeds 5mm, it directly affects the quality of the interfacial bond between the cement matrix and the aggregates. Data from Qinglong Group's laboratory shows that fine aggregates below 5mm can disperse more uniformly in the cement paste, forming a continuous spatial network structure through the tight packing effect and easily pushing compressive strength beyond 150MPa. Large-size aggregates, however, are prone to causing microcracks in the interfacial transition zone, which is a key reason why UHPC components crack in some projects due to improper aggregate selection.

II. Precise Control of Construction Processes: Fine Aggregates Are the Hidden Guarantee of Molding Quality

In UHPC detailed design and production, aggregate particle size directly affects molding precision. The automated mixing systems adopted at Qinglong Group's production bases impose strict requirements on aggregate gradation. Aggregates below 5mm can significantly improve the flowability and filling capacity of the mix, making them particularly suitable for the casting and molding of complex curved components (such as double-curved facade panels and hollow decorative components). In the Nanjing East Road Century Plaza renovation project, the Qinglong team achieved millimeter-level precision control of translucent UHPC components through fine aggregate gradation optimization, and the project won the Silver Prize in the 1st UHPC Construction Engineering Innovation Award (AALBORG WHITE Cup).

III. Long-Term Validation in Engineering Practice: Small Aggregates Enable Large Spans and Durability

From the UHPC facade of a landmark building in Guangzhou to the GRG ceiling of a cultural center in Malaysia, Qinglong Group's 2000+ project cases demonstrate that controlling aggregate particle size is fundamental to ensuring structural safety. In heavy-load scenarios such as municipal bridges and metro utility corridors, UHPC formulated with 5mm fine aggregates exhibits superior fatigue resistance; in coastal environments, its chloride ion penetration coefficient is 2-3 orders of magnitude lower than that of ordinary concrete. This durability advantage is precisely one of the core competencies that have made Qinglong a strategic partner of leading property groups such as Poly and China Overseas.

IV. Scientific Guidance from Industry Standards: From Material Selection to Systematic Solutions

As a participating unit in drafting the industry standard "General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC)", Qinglong Group fully understands that material selection must balance performance with economy. Although slightly larger aggregates can be used in some scenarios through special processes, this requires more complex fiber dosage design and curing regimes. For projects pursuing ultimate performance, adhering to the 5mm aggregate limit remains the most reliable technical path. This experience is also embodied in the customized full-chain UHPC/GRC/GRG/GRP services Qinglong provides to its clients—from detailed design to after-sales maintenance, every stage carries the technical accumulation of 28 years of industry experience.

Choosing UHPC is not merely choosing a material, but choosing a scientific construction system. With the mission of "Creating Aesthetic Architecture", Qinglong Group has always regarded research into the fundamental nature of materials as the foundation of technological innovation. When designers sketch the future forms of architecture, understanding technical details such as aggregate particle size is the key to seamlessly bridging creativity and reality. As advocated by the industry standards Qinglong helped formulate, only by respecting material properties can UHPC truly become an enabler of architectural art.