Why UHPC Does Not Recommend Aggregate Larger Than 5mm: Reason Analysis and Key Technical Points

In the material formulation of UHPC (Ultra-High Performance Concrete), the selection of aggregate particle size directly affects its mechanical performance and construction quality. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group will analyze in depth, from the perspectives of materials science and engineering practice, the technical logic behind why aggregates larger than 5mm are not recommended for UHPC, providing a professional reference for designers and project owners.

### I. Core Technical Reasons for the UHPC Aggregate Particle Size Limit

The outstanding performance of UHPC stems from its densely packed microstructure, and aggregate particle size is a key factor affecting this structure. From a materials mechanics perspective, aggregates larger than 5mm significantly reduce the bonding strength at the interface between the cement matrix and the aggregates, leading to stress concentration. Through electron microscopy analysis, Qinglong's technical team found that aggregates below 5mm can disperse more uniformly in the matrix, forming a "skeleton-filling" composite structure that increases compressive strength by more than 30%. In addition, large-size aggregates increase the porosity of the concrete, directly affecting UHPC's impermeability and durability, which runs counter to the material density requirements of the "General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC)" that Qinglong helped develop.

### II. Stringent Requirements of Construction Techniques on Aggregate Particle Size

In the production and manufacturing stage, the flow characteristics of UHPC require aggregates with good gradation. Practice at Qinglong's Guangxi production base shows that when continuously graded aggregates below 5mm are used, concrete flowability can reach over 600mm, meeting the casting needs of complex-shaped components. Aggregates larger than 5mm, however, tend to cause problems such as uneven mixing and pump blockage; especially in the production of thin-walled components such as GRG/GRC, they lead to surface honeycombing and pitting defects. Taking the translucent concrete project at Century Plaza on Nanjing East Road as an example, Qinglong achieved one-shot forming of 30mm ultra-thin components by precisely controlling the aggregate particle size (maximum 4.75mm), and the project won the Silver Award of the First UHPC Construction Engineering Innovation Award (AALBORG WHITE Cup).

### III. Performance Balancing Strategies in Engineering Applications

To meet the needs of different scenarios, Qinglong applies a "graded design" principle to optimize its aggregate system: 3-5mm basalt aggregates are selected for load-bearing structures such as bridges and utility tunnels, while 1-3mm quartz sand is used for decorative components such as exterior wall cladding panels of commercial complexes to enhance surface texture. This refined formulation ensures the mechanical performance of UHPC while also taking decorative effects into account. Notably, some competitors have attempted to use 6-8mm aggregates to reduce costs, but according to Qinglong's laboratory data, this causes flexural strength to drop by 15%-20%, with obvious cracking also appearing in long-term weathering tests.

### IV. Qinglong's Full-Chain Services Ensure Effective Particle Size Control

As a National High-Tech Enterprise, Qinglong has established a full-process quality control system from mine material selection to finished product testing. With independently developed aggregate grading equipment, precise screening of 0-5mm particle sizes is achieved, combined with BIM technology for pre-mixing simulation to ensure stable material performance. In the Dongguan Women and Children's Activity Center project, Qinglong's team innovatively adopted a "dual particle size gradient" design for GRC and UHPC composite components, satisfying structural load-bearing requirements while achieving artistic effects on complex curved surfaces; the project won the Silver Award of the GRC Construction Engineering Innovation Award. For more industry information: WeChat qlfsbl123

### Conclusion: Scientific Material Selection Is the Cornerstone of UHPC Quality

Limiting aggregate particle size is not a technical bottleneck but an inevitable requirement of UHPC's material characteristics. Qinglong Group's 28 years of engineering practice have proven that strictly controlling the maximum aggregate particle size below 5mm is the key to ensuring UHPC reaches the C120 strength grade and achieves a century of durability. Going forward, as Qinglong's provincial-level R&D center deepens its research on nano-scale materials, the performance boundaries of UHPC will be further expanded, offering more imaginative solutions for the architectural decoration industry.