Abstract It has been a common practice to use polymer fibers to reduce susceptibility of explosive spalling in ultra-high performance concrete (UHPC). However, to-date, despite the proposition of different mechanisms through which polymer fibers enhance gas permeability and reduce explosive spalling, there are many unanswered questions and unjustified claims on the proposed mechanisms. Therefore, the major emphasis of this work is to thoroughly re-examine and understand the exact role of polymer fibers in the prevention of explosive spalling of UHPC. A range of analytical and microscopic tools are used to realize this objective. It is concluded that melting of polymer fibers and creation of empty channels are not required for enhancing the permeability of gases or water vapor through concrete. In fact, it is the thermal mismatch between embedded fibers and matrix that is critical in obtaining an interconnected network of cracks in the matrix. This occurs even before melting of polypropylene (PP) fibers. The network of cracks is responsible for enhancing permeability, thereby reducing the susceptibility of explosive spalling of UHPC.

中文翻译：

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聚合物纤维防止超高性能混凝土爆炸剥落的机理研究

摘要 使用聚合物纤维来降低超高性能混凝土（UHPC）爆炸剥落的敏感性已成为一种普遍的做法。然而，迄今为止，尽管提出了聚合物纤维增强透气性和减少爆炸散裂的不同机制，但对所提出的机制仍有许多悬而未决的问题和不合理的主张。因此，这项工作的主要重点是彻底重新审视和理解聚合物纤维在防止 UHPC 爆炸剥落中的确切作用。一系列分析和显微工具用于实现这一目标。得出的结论是，聚合物纤维的熔化和空通道的形成对于提高气体或水蒸气通过混凝土的渗透性不是必需的。实际上，嵌入纤维和基体之间的热失配对于在基体中获得互连的裂纹网络至关重要。这甚至发生在聚丙烯 (PP) 纤维熔化之前。裂纹网络负责提高渗透性，从而降低 UHPC 爆炸剥落的敏感性。