Abstract Polypropylene (PP) fibers are commonly used for the prevention of thermal spalling of ultra-high performance concrete (UHPC). In this work, the effect of fiber distribution on permeability and spalling resistance is investigated and an analytical model for permeability at 150 °C is proposed. This model, considering the parameters like fiber dimensions, dosage, and percolation, is based on Kozeny-Carman equation. It was found that the percolation of the interconnecting fiber network resulted in a significant increase in permeability of UHPC. X-ray tomography data on the three-dimensional spatial distribution of fibers reiterated that fiber aspect ratio and dosage (and fiber number density) were critical in increasing the fiber connectivity (percolation). It was also found that a vapor permeability of larger than 0.6 × 10−16 m2 at 150 °C could eliminate spalling. Further, based on a semi-empirical approach, aspect ratio between 300 and 600 was recommended for spalling prevention with a fiber dosage of 0.3–0.4 vol%.

中文翻译：

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聚合物纤维空间分布对防止UHPC高温剥落的影响

摘要 聚丙烯 (PP) 纤维通常用于防止超高性能混凝土 (UHPC) 的热剥落。在这项工作中，研究了纤维分布对渗透率和抗剥落性的影响，并提出了 150 °C 时渗透率的分析模型。该模型考虑了纤维尺寸、剂量和渗透等参数，基于 Kozeny-Carman 方程。发现互连纤维网络的渗透导致 UHPC 渗透性显着增加。纤维三维空间分布的 X 射线断层扫描数据重申，纤维纵横比和剂量（和纤维数密度）对于增加纤维连通性（渗透）至关重要。还发现蒸汽渗透率大于 0。6 × 10−16 m2 在 150 °C 可以消除剥落。此外，基于半经验方法，建议使用 300 到 600 之间的纵横比以 0.3-0.4 vol% 的纤维剂量防止剥落。