This paper examines the effect of heating rate on the microstructure of cement-based systems exposed to sustained elevated temperatures. Besides a conventional mortar designed to attain a compressive strength of 30 MPa at 28 d, a high-strength mortar was also designed to achieve a corresponding strength of 90 MPa. Samples were extracted for testing under three different heating rates, ranging from 1°C/min to 10°C/min, to a sustained elevated temperature up to 400°C. This study finds that the microstructure of high-strength mortar is more sensitive to the heating rate in comparison with that of the normal-strength mortar. The porosity of the mortar mixtures uniformly increases with an increase in the temperature of exposure. However, there was a decrease in the porosity, at any sustained elevated temperature, with an increase in the heating rate. It is seen that the fractal dimension of the pores increases with an increase in the sustained temperature. Additionally, this fractal dimension was seen to increase with an increase in the heating rate. However, this trend was more pronounced at lower temperatures of exposure, so that the rate of heating appears to become less conspicuous at higher temperatures of soaking.

中文翻译：

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加热速率对高温砂浆中空隙网络的影响

本文研究了加热速率对暴露在持续高温下的水泥基系统微观结构的影响。除了常规砂浆设计为在 28 d 时达到 30 MPa 的抗压强度外，还设计了一种高强度砂浆以达到相应的 90 MPa 强度。提取样品以在三种不同的加热速率下进行测试，范围从 1°C/min 到 10°C/min，持续升温至 400°C。本研究发现，与普通强度砂浆相比，高强度砂浆的微观结构对升温速率更为敏感。砂浆混合物的孔隙率随着暴露温度的升高而均匀增加。然而，在任何持续升高的温度下，孔隙率都会随着加热速率的增加而降低。可以看出，孔隙的分形维数随着持续温度的增加而增加。此外，该分形维数随着加热速率的增加而增加。然而，这种趋势在较低的暴露温度下更为明显，因此在较高的浸泡温度下，加热速率似乎变得不那么明显。