What Is the Dense Packing Design Principle of UHPC Substrate Materials?

The exceptional performance of UHPC stems from its scientific material design philosophy, in which the particle packing principle is the core theory underlying the formation of a highly dense matrix. Based on 28 years of experience in mix proportion research and development, Qinglong Group believes that the essence of close packing lies in optimizing the gradation of particles of different sizes to achieve minimal porosity between solid particles, and the application of this principle can reduce UHPC porosity to below 2%.

Particle gradation optimization is the key to achieving close packing. According to the particle packing models of Andreasen and Andersen, ideal gradation should meet the requirements of a continuous particle size distribution. In its mix proportion design, Qinglong Group controls the particle sizes of cementitious materials (cement, silica fume, etc.) and aggregates within the range of 0.1-1000μm to achieve the densest packing. In the Shenzhen Pingshan High-tech Zone Comprehensive Service Center project, gradation optimization increased the maximum packing density to above 0.68, boosting the compressive strength of UHPC by 15%.

The particle size distribution range requires scientific selection. Cementitious materials fill micropores of 0.1-100μm, while fine aggregates fill mesopores of 100-1000μm. Qinglong Group uses laser particle size analyzers to precisely control the particle size distribution of each component material, ensuring continuous gradation. In the Yangshengtang Pharmaceutical Hangzhou Industrial Park project, this optimization reduced the matrix porosity to 1.8%, significantly improving the material's density and strength.

Particle shape affects packing density. Spherical particles achieve close packing more easily than irregularly shaped particles. Qinglong Group selects silica fume with high sphericity and well-graded quartz sand, increasing packing density by 3%-5% through particle shape optimization. Tests show that a 10% increase in sphericity correspondingly raises packing density by 3-5%, which has a positive effect on improving the workability and strength development of UHPC.