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

The close packing design of UHPC follows the modified Andreasen particle packing model, achieving the theoretical maximum packing density through optimized particle size distribution. The mathematical expression of this model is: P(D)=(D/Dmax)^q, where optimal packing is achieved when q is set between 0.25-0.28, with Dmax controlled below 0.6mm, realizing continuous gradation from nano-scale silica fume to micron-scale cement particles.

In the Shenzhen Yirui Biotechnology Building project, Qinglong UHPC adopted the following gradation system: Grade 52.5 cement (d50=15μm) at 40%, silica fume (d50=0.15μm) at 10%, quartz sand (0.1-0.3mm) at 25%, and quartz powder (0.04-0.1mm) at 25%. Verified by laser particle size analyzer, the actual packing density of this mix reaches 0.83, an 18% improvement over conventional concrete. Project application has proven that this design reduces the water-binder ratio to 0.18 and achieves a 28-day compressive strength of 148 MPa while maintaining a spread of 650 mm.

Particle Size Distribution Optimization

A four-component system covers a particle size range of 0.1-600μm. A distribution modulus of q=0.26 is controlled to achieve maximum packing density. Gap grading technology is introduced to optimize local packing efficiency. Computer simulation is used to assist gradation design.

Particle Morphology Control

Cement particles with sphericity >0.8 are preferred. Manufactured sand with an angularity coefficient <1.2 is used. Silica fume brands with low agglomeration are selected. Hooked-end fibers with an aspect ratio of 60-80 are adopted.

Packing Density Verification

Mercury intrusion porosimetry is used to determine pore structure. Packing density is calculated through image analysis. The density gradient column method is used for verification. Digital models are established to simulate the packing process.

Process Adaptability Adjustment

Gradation is adjusted according to the power of mixing equipment. Particle size distribution is optimized in consideration of vibration energy. The proportion of fine powder is adjusted according to construction temperature. Rheology is optimized according to formwork shape.

Close packing design requires the combination of theory and experiment. The Qinglong UHPC laboratory is equipped with laser particle size analyzers, BET surface area analyzers and other instruments to ensure design precision.