Design of self-compacting ultra-high performance concrete (SCUHPC) towards to the cementitious materials packing optimization

UHPC is a cement-based material characterized by outstanding strength and durability, but its high viscosity poses challenges for field application. Herein, we built a Horsfield theory modified cementitious packing structure by utilizing fly ash microsphere (FAM), aiming to release water, thus, reduce viscosity. The wet packing density indicated that FAM could optimize the packing structure, and transform locked water into free water. Meanwhile, 1H NMR revealed the variation of adsorbed water to free water due to the surface characteristics of FAM. Consequently, more free water could be obtained, which thereby reduced the viscosity up to 75 %. The slump flow, t500, v-funnel flow time and J-ring tests were further conducted to assess the workability, where the results indicated the modified UHPC met the standards for self-compacting concrete. Besides, the synergistic water-reducing strategy attributed to cementitious materials packing optimization can maintain a low w/b (<0.2), which contributes to an ultrahigh strength of 120.5 MPa, realizing the feasibility of developing selfcompacting UHPC This study provides a new approach to enhance the workability of UHPC without sacrificing mechanical property and durability, expanding the field application of UHPC.