Accurate modelling of transient creep strain (TRC) is crucial for reliable fire performance assessments of concrete structures, since it is the largest strain component for structural concrete subjected to thermal exposure. Nonetheless, the mechanism underlying TRC is still not fully understood and most of the available models were established based on ordinary Portland cement concrete. As the most widely used supplemental cementitious material, the effect of fly ash on the development of TRC still requires further study. For this paper, steady state tests and transient state tests were carried out on ordinary Portland cement concrete (CEM I 52.5 as per BS EN 197-1, water/cement = 0.5) and fly ash concrete (class F fly ash as per BS EN 450-1, 25% replacement percentage), respectively. It was found that replacing 25% ordinary Portland cement with class F fly ash in concrete can mitigate the development of TRC above 400°C. Based on the experimental results, one assumption of the influence mechanism of class F fly ash on TRC is made and a TRC model for fly ash concrete (class F, 25% replacement percentage) at elevated temperatures is proposed.

中文翻译：

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高温下粉煤灰混凝土的瞬态蠕变应变

瞬态蠕变应变 (TRC) 的准确建模对于混凝土结构的可靠防火性能评估至关重要，因为它是受热暴露的结构混凝土的最大应变分量。尽管如此，TRC 的潜在机制仍未完全了解，大多数可用模型都是基于普通硅酸盐水泥混凝土建立的。作为应用最广泛的补充胶凝材料，粉煤灰对TRC发展的影响仍需进一步研究。在本文中，对普通硅酸盐水泥混凝土（根据 BS EN 197-1 的 CEM I 52.5，水/水泥 = 0.5）和粉煤灰混凝土（根据 BS EN 的 F 级粉煤灰）进行了稳态测试和瞬态测试450-1, 25% 的替换率），分别。研究发现，在混凝土中用 F 级粉煤灰替代 25% 的普通硅酸盐水泥可以减缓 400°C 以上 TRC 的发展。根据试验结果，假设F级粉煤灰对TRC的影响机理，提出了高温粉煤灰混凝土（F级，25%替代率）的TRC模型。