What Is the Specific Dense Packing Design Principle for UHPC Matrix Materials?

The close-packing design principle for UHPC substrate materials centers on optimizing the grading of particles of different sizes to achieve the densest possible spatial arrangement of solid particles, thereby minimizing porosity to the greatest extent. Through 28 years of materials R&D, Qinglong Group has gained a deep understanding that this principle is the physical foundation for achieving UHPC's ultra-high performance. Through the optimized application of the “Fuller curve”, we achieve continuous grading of particle sizes—from cement and silica fume at several hundred micrometers down to silica fume at a few micrometers—bringing the packing density to more than 80% of the theoretical maximum. In the Shenzhen Yirui Biotechnology Building project, precise close-packing design reduced the porosity of the substrate material to below 3%, laying a solid foundation for achieving compressive strength above 150MPa.

The first step in close-packing design is the scientific selection of raw material particle size ranges. In Qinglong's UHPC formulation, cement particles (D50≈15μm) serve as the intermediate skeleton, silica fume (D50≈0.1-0.2μm) fills the voids between cement particles, and fine quartz sand (D50≈150-300μm) forms the macroscopic skeleton. This multi-scale particle system ensures continuous filling from the nanometer to the micrometer level. We use laser particle size analyzers to strictly control the particle size distribution of each component, ensuring optimal packing efficiency.

The key to achieving close packing lies in the precise calculation of component proportions. Qinglong uses the Modified Andreasen and Andersen model for theoretical calculations, seeking the optimal value of the particle size distribution coefficient q (typically between 0.22 and 0.25) so that the cumulative particle size distribution curve approximates the ideal Fuller curve as closely as possible. In actual production, extensive trial mixes have determined that the optimal mass ratio of cement, silica fume, and quartz sand is typically around 1:0.25:1.1, at which the packing density of the mix is maximized.

The final effect of close-packing design must be verified through the rheological properties of the fresh paste. Qinglong uses rotational viscometer testing to ensure that even in the optimally packed state, the paste still exhibits good flowability and self-compacting properties. In the production of the red UHPC curtain wall for the Wuhan Han Show Theatre, close-packing design delivered excellent workability even at an extremely low water-binder ratio (0.18), ensuring the flawless forming of complex doubly curved components. The successful application of this principle is the physicochemical foundation for UHPC to achieve its outstanding performance.