The addition of polypropylene (PP) fibres has been shown to reduce the fire spalling propensity of concrete. When including this type of fibres in the concrete, the concrete mix becomes less robust, and small deviations in the constitutes change the workability and properties of the concrete. So, from a manufacturing perspective as small dosages as possible of PP fibres are desirable. Very few large-scale fire resistance tests of concrete loaded in compression exist showing the function of PP fibres at low dosages on concrete mixes sensitive to spalling if no fibres are added. In this paper, results from 26 fire tests are presented and analysed. The test results are from four different experimental campaigns, but all the mixes have in common that the water-to-cement ratio is 0.40. The results show that an amount of only 0.6 kg/m³ PP fibres has a significant effect on the spalling propensity and that even lower amounts reduce the spalling although they do not eliminate it entirely. During one of the fire tests on large slabs loaded in compression, unloaded small cubes of the same mixes were also included in the furnace. None of the small specimens spalled, whereas some of the corresponding large slabs spalled beyond the layer of reinforcement. This illustrates that tests on small, unloaded specimens are not relevant when assessing fire spalling of larger cross-sections loaded in compression.

中文翻译：

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使用小剂量聚丙烯纤维减少混凝土的火灾剥落

添加聚丙烯 (PP) 纤维已被证明可以降低混凝土的火灾剥落倾向。当在混凝土中加入这种类型的纤维时，混凝土混合物变得不那么坚固，并且组成中的小偏差会改变混凝土的可加工性和性能。因此，从制造的角度来看，PP 纤维的剂量尽可能小是可取的。很少有大规模的压缩荷载混凝土耐火试验表明，如果不添加纤维，低剂量的 PP 纤维对易剥落的混凝土混合物的作用。本文介绍并分析了 26 次火灾试验的结果。测试结果来自四个不同的实验活动，但所有混合物的共同点是水灰比为 0.40。结果表明，用量仅为 0.6 kg/m³ PP 纤维对剥落倾向有显着影响，即使较低的用量也不会完全消除剥落现象。在对压缩加载的大板进行的一项防火测试中，炉中还包括相同混合物的未加载小立方体。没有一个小试件剥落，而一些相应的大板剥落超出了钢筋层。这说明在评估受压加载的较大横截面的火剥落时，对小型未加载试样进行的测试是不相关的。