What Is the Close Packing Design Principle of UHPC Substrate Materials? Particle Gradation Optimization and Qinglong Group's Densification Technology

The close packing design principle of UHPC substrate materials is based on the maximum density theory in particle science. By optimizing the grading curves of particles of different sizes, it achieves the maximum packing density of the aggregate-cementitious material-mineral admixture system, thereby significantly reducing porosity and improving mechanical properties. Over 28 years of UHPC research and development, Qinglong Group has adopted the modified Andreasen equation to control particle distribution, achieving continuous grading across a particle size range from nano-scale silica fume (0.1-1μm) to fine aggregate (0.1-1mm), bringing packing density above 0.85 and reducing porosity to within 5%. In the Wuhan Hanxiu Theater project, the UHPC matrix produced with this technology achieved a compressive strength of 150MPa, far exceeding the density level of traditional concrete.

The core of close packing lies in the scientific combination of particle size ranges. We adopt a 'three-level grading' system: micron-scale active admixtures (silica fume, fly ash) fill the gaps between cement particles, sub-millimeter quartz sand forms the skeleton, and nano-scale materials further fill micropores. Through laser particle size analysis to optimize the mix ratio, the particle distribution curve approaches the ideal Fuller curve, achieving optimal spatial arrangement between particles. This design allows the water-binder ratio of Qinglong UHPC to be reduced to 0.18-0.22, greatly enhancing material density.

Production processes ensure packing effectiveness. Qinglong Group has introduced the German BHS high-speed mixing system to ensure uniform particle dispersion; vacuum dewatering technology expels entrapped air bubbles; and steam curing promotes continued filling by unhydrated particles. At our Nanning production base, digital control systems keep packing density fluctuation within ±0.02, ensuring product consistency.

Close packing design not only improves strength but also significantly enhances durability. Qinglong UHPC has a chloride ion diffusion coefficient as low as 2.0×10⁻¹²m²/s and an impermeability grade of P20 or above, providing long-lasting protection for buildings. The application of this principle is the foundation for UHPC to achieve ultra-high performance.