Comparative optimization of densified system of ultra-fine particles (DSP) and Horsfield filling toward UHPC fabrication

Using small size particle as secondary filler to fill in the gap between cement particles according to either DSP or Horsfield filling theory will optimize the packing structure, thereby enhancing the properties of UHPC. However, there are key differences between the two theories regarding to the ratio between the particle size of cement and secondary filler, making it questionable to improve the performance of UHPC. Herein, we developed DSP guided UHPC and Horsfield inspired UHPC via the use of silica fume and fly ash microsphere, respectively, we compared and evaluated the packing structure and corresponding performance. We found that less well-known method Horsfield filling theory contributed to the overall best performers of UHPC compared with that of DSP inspired UHPC. 1H NMR spectra and wet packing density calculation results demonstrated that Horsfield packing contributed to a more homogeneous and denser microstructure, and significantly reduced autogenous shrinkage, cost, and energy burden compared with that of DSP-modified UHPC. We also found that typical DSP fell far short of its theoretical state due to SF agglomeration. This study explores the potential of Horsfield packing in optimizing the packing structure of UHPC, providing an economical option for enhancing the performance of concrete.