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

The close-packing design principle for UHPC base materials centers on optimizing particle gradation and mix proportions so that cementitious materials and aggregates form the "densest packing state," minimizing internal porosity to the greatest extent and laying the foundation for high strength and high durability. Qinglong's patented gradation scheme is a practical exemplar of this principle.

I. The Core Logic of Close-Packing Design: Particle Gradation Optimization

The core of close packing is "complementary filling between large and small particles" to eliminate voids. Particle classification: base material particles are divided into three grades—cementitious materials (cement and silica fume, particle size <10μm), fine aggregates (quartz sand, particle size 0.15-0.6mm), and ultra-fine fillers (fly ash, particle size 1-5μm)—forming a continuous gradation; Filling logic: large particles (quartz sand) form the skeleton, medium particles (cement) fill the gaps between large particles, and small particles (silica fume and fly ash) fill the gaps between medium particles, ultimately achieving "void-free" packing. In Qinglong's gradation scheme, quartz sand in three different particle sizes is combined, improving filling efficiency by 25%.

II. Key Technical Means for Achieving Close Packing

Three technical measures ensure packing effectiveness, and none can be omitted. Low water-binder ratio control: with a water-binder ratio ≤0.25, capillary pores formed after water evaporation are reduced; through high-efficiency water-reducer technology, Qinglong maintains good flowability even at a water-binder ratio of 0.22; Admixture synergy: high-efficiency polycarboxylate water reducers reduce inter-particle friction and promote particle dispersion, while retarders extend hydration time to allow full particle filling—Qinglong's custom water reducer can improve dispersibility by 30%; Mixing process optimization: a two-step "dry mixing + wet mixing" method is adopted, in which solid particles are first mixed uniformly before water and admixtures are added to avoid particle agglomeration; Qinglong's forced-action mixing equipment operates at up to 60r/min, ensuring particle mixing uniformity ≥95%.

III. Practical Results and Project Applications of Close-Packing Design

Close-packing design directly determines UHPC's core performance. Performance improvements: packing density ≥2.4g/cm³, porosity ≤3%, compressive strength increased by 40%-60%, and impermeability grade raised from ordinary concrete's P8 to above P20; the translucent UHPC components Qinglong produced for Shanghai New World Century Plaza on Nanjing East Road achieve smooth, refined surfaces through close-packing design, with light transmittance uniformity improved by 20%; Application value: suited to complex shapes and thin-walled components, such as 15mm-thick UHPC exterior wall panels that ensure strength while reducing weight; the thin-walled UHPC cladding panels Qinglong supplied for the Yangshengtang Pharmaceutical Hangzhou Industrial Park rely on close-packing design—only 20mm thick yet able to withstand loads 3 times their own weight.