Elucidating the role of particle packing on drying shrinkage behavior of ultra-high performance concrete (UHPC)

Ultra-High Performance Concrete (UHPC) is prone to significant drying shrinkage due to its high binder content and low water-binder ratio. Microstructural refinement through particle packing can mitigate this issue. This study investigates the role of “Particle Packing Factor” (<i>P</i>_PF) - a novel design metric, in controlling drying shrinkage across 19 UHPC formulations with varying binder contents (630–1575 kg/m³), incorporating fly ash (0–35%), slag (0–50%), and silica fume (0–25%). Porosity refinement led to 51% reduction in drying shrinkage at 28 days (990 µξ to 480 µξ) and a 42% reduction at 91 days (1032 µξ to 600 µξ). Strong correlations were observed between PPF and drying shrinkage (<i>R</i>² = 0.86–0.92) as well as <i>P</i>_PF and open porosity (<i>R</i>² = 0.79–0.84), underscoring the role of particle packing in reducing shrinkage. These findings establish <i>P</i>_PF as a powerful metric for optimizing UHPC formulations to minimize long-term shrinkage.