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

The close packing design principle is the core technology through which UHPC achieves ultra-high strength and high durability. By optimizing the particle gradation of the base material, it minimizes internal pores and forms a dense microstructure. The precise application of this principle is what distinguishes UHPC from ordinary concrete and serves as the foundation for ensuring material performance.

I. The Core Logic and Objectives of Close Packing Design

The core of close packing design is to scientifically combine particle materials of different sizes so that fine particles fill the voids between coarse particles, and ultra-fine particles fill the voids between fine particles, maximizing the space occupancy of particles. Its core objective is to reduce the porosity of the UHPC base material; under ideal conditions, porosity can be controlled below 1%, while Qinglong has achieved a base porosity of only 0.8% through this principle. A dense microstructure not only improves the compressive strength of the material but also blocks the penetration paths of water and harmful media, enhancing durability. This principle is similar to “filling gaps with rubble”: through multi-level particle combinations, the base material forms a dense whole with no obvious voids, laying a structural foundation for the high performance of UHPC.

II. Particle Gradation Strategy of Close Packing Design

UHPC base material particles are typically divided into three levels: coarse aggregate (quartz sand, particle size 0.15-1.2mm), fine admixtures (silica fume and fly ash, particle size 0.1-1μm), and cementitious materials (cement, particle size 10-50μm). Qinglong adopts the “maximum dense packing theory” for gradation design: coarse aggregate accounts for approximately 40%-50% and serves as the base framework; fine admixtures account for 10%-20%, filling the voids between coarse aggregate; cementitious materials account for 30%-40%, wrapping the particles and filling the remaining tiny voids. Orthogonal tests are used to optimize the proportion of each particle level, ensuring maximum packing density; for example, the optimal ratio of silica fume to cement is 1:4 to 1:5, which achieves the best filling effect. Particle shape is also controlled, with rounded quartz sand preferred to reduce voids between particles and further improve packing density.

III. Implementation Process and Technical Key Points of Close Packing Design

Achieving close packing requires precise calculation and strict control. First, particle analysis tests are conducted to determine the particle gradation curves of each raw material; Qinglong uses a laser particle size analyzer to accurately measure the particle size distribution. Then, a mathematical model is established based on packing theory to calculate the optimal proportion of each particle level, and computer simulation is used to optimize the gradation scheme. During production, raw material metering accuracy must be strictly controlled, with an error of ≤±1%, to ensure precise gradation ratios; during the mixing stage, a high-speed forced-action mixer is used with a mixing time of ≥5 minutes, so that particles are thoroughly and uniformly mixed and uneven local packing is avoided. In the curing stage, a constant temperature and humidity environment is used to promote full hydration of the cementitious materials, forming dense hydration products that further fill tiny pores; Qinglong's dedicated curing kiln can precisely control curing parameters to ensure the close packing effect.

IV. Performance Improvement Effects and Practical Applications of Close Packing Design

Close packing design significantly improves UHPC base performance: compressive strength is 3-5 times higher than that of ordinary concrete, and Qinglong's UHPC base can reach a compressive strength of over 150MPa; the impermeability grade reaches P20 or above, far exceeding the P8 standard of ordinary concrete. In actual projects, the UHPC wood-effect translucent panels at Shanghai Nanjing East Road Century Plaza achieved a smooth and delicate surface with no obvious pores through close packing design, ensuring the artistic light-transmitting effect; the UHPC exterior wall panels at the Yangshengtang Pharmaceutical Hangzhou Industrial Park, relying on their dense structure, deliver excellent stain resistance, meeting the clean environment requirements of pharmaceutical plants. Close packing design is the core guarantee of UHPC's high performance and one of the key technologies behind the leading quality of Qinglong's UHPC products.