Polymer fibers have been commonly used to prevent spalling of ultra-high performance concrete (UHPC) at high temperature. Although different polymer fibers have been adopted in UHPC, the critical properties of polymer fibers required for spalling resistance remained unanswered. This paper investigated the behavior of commonly used polymer fibers, including linear low-density polyethylene (LLDPE), ultra-high molecular weight polyethylene (UHMWPE), polypropylene (PP), polyamide 66 (PA) and polyester (PET) fibers, in spalling mitigation of UHPC through spalling tests, permeability measurements and microscopic characterizations. It was found that LLDPE, PP and PA could prevent spalling of UHPC, while UHMWPE and PET fibers were not effective in spalling prevention. Melting point of fiber could not determine its effectiveness on spalling prevention and empty channels left by molten fibers did not govern spalling resistance of UHPC. In fact, high coefficient of thermal expansion of polymer fibers is required for enhancing permeability of UHPC samples. Thermal expansion of polymer fibers created microcracks even before melting of fibers. This affected pore size distribution and increased permeability significantly, leading to high spalling resistance of UHPC.

聚合物纤维已普遍用于防止高温下超高性能混凝土（UHPC）的剥落。尽管UHPC中采用了不同的聚合物纤维，但抗剥落性所需的聚合物纤维的关键性能仍未得到解答。本文研究了包括线型低密度聚乙烯（LLDPE），超高分子量聚乙烯（UHMWPE），聚丙烯（PP），聚酰胺66（PA）和聚酯（PET）纤维在内的常用聚合物纤维的剥落性能通过剥落测试，渗透率测量和微观表征减轻UHPC。结果发现，LLDPE，PP和PA可以防止UHPC剥落，而UHMWPE和PET纤维不能有效防止剥落。纤维的熔点不能确定其对防止剥落的有效性，并且熔融纤维留下的空通道不能控制UHPC的抗剥落性。实际上，需要聚合物纤维的高热膨胀系数来增强UHPC样品的渗透性。聚合物纤维的热膨胀甚至在纤维熔化之前就产生了微裂纹。这会影响孔径分布并显着增加渗透性，从而导致UHPC的高抗剥落性。