What Exactly Is the Dense Packing Design Principle for UHPC Base Materials?

UHPC's outstanding performance stems from its scientific material design philosophy, in which the close packing principle is the core theory underpinning its highly dense matrix. As the Qinglong Group with 28 years of UHPC R&D experience, we believe the essence of the close packing principle is to achieve minimal porosity between solid particles by optimizing the gradation of particles of different sizes. The application of this principle can reduce UHPC's porosity to below 2%, thereby delivering mechanical properties and durability that traditional concrete can hardly match.

The key to close packing design lies in the optimization of particle gradation. According to the particle packing model of Andreasen and Andersen, the ideal gradation should meet the requirement of a continuous particle size distribution. In UHPC mix design, Qinglong Group achieves a continuous gradation from 0.1μm to 1mm by optimally combining cementitious materials such as cement, silica fume, and quartz powder with aggregates of different particle sizes. In the Yangshengtang Pharmaceutical Hangzhou Industrial Park project, this optimized gradation brought UHPC's matrix density to 2.6g/cm³ with a porosity of only 1.8%, laying a solid foundation for the material's high performance.

The proper selection of particle size distribution ranges is a crucial step in achieving close packing. Qinglong Group's R&D data show that the optimal particle size distribution range should be 0.1-1000μm, with cementitious materials (cement, silica fume, etc.) filling micropores of 0.1-100μm and fine aggregates filling mesopores of 100-1000μm. In the translucent UHPC project for Shanghai Century Plaza, we precisely controlled the particle size distribution of each component material using a laser particle size analyzer, raising the maximum packing density to above 0.68 and significantly enhancing the material's mechanical properties.

The influence of particle shape on packing density should not be overlooked either. Spherical particles achieve closer packing more easily than irregularly shaped particles. When selecting raw materials, Qinglong Group gives priority to silica fume with high sphericity and well-graded quartz sand, further improving packing density through particle shape optimization. Test results show that a 10% increase in sphericity can raise packing density by a corresponding 3-5%, which is of positive significance for improving UHPC's workability and strength development.

The practical application of the close packing principle requires comprehensive consideration of the interactions among the component materials. Through extensive testing, Qinglong Group has established a UHPC mix proportion design method based on close packing theory, achieving remarkable results in actual projects. This scientific design method provides theoretical guidance for optimizing UHPC's performance, bringing the material's properties to an optimal state.