Understanding the microstructure evolution during the cyclic freezing-thawing process is crucial to studying the deterioration mechanisms of concrete under cyclic freezing-thawing. In this study, air voids were entrained into cement mortar and paste by AEA and polymeric microspheres. Mercury intrusion porosimetry (MIP) and micro-CT techniques were integrated to investigate the microstructure of the specimens with various freezing-thawing cycles. After subjecting the Ref. and AEA mixed mortar to 100 and 200 freezing-thaw cycles, an increase in porosity and pore entrapment was observed from the MIP results, suggesting the occurrence of damage induced by cyclic freezing-thawing. Conversely, in the microspheres mixed mortar, the presence of surface adsorbed moisture led to an initial increase in porosity and pore entrapment after 100 freezing-thaw cycles, followed by a decrease after 200 cycles, indicating a healing effect. Micro-CT analysis revealed that while the AEA mixed specimens exhibited higher air content than the microspheres mixed specimens, the latter showed a greater number of voids, which ultimately enhanced their resistance to freezing-thawing. The micro-CT results unveiled that air bubbles tended to merge in AEA mixed specimens, adversely affecting their resistance to freezing-thawing. Conversely, the microsphere-incorporated specimens displayed smooth void distribution curves, indicating a well-distributed air void system that enhances their freezing-thawing resistance. This work suggests that microspheres can be a great candidate for air-entraining materials. Combining the MIP and micro-CT analysis can better understand the microstructure change of concrete with cyclic freezing-thawing.

中文翻译：

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揭示加气砂浆和浆料的微观结构演变：来自 MIP 和微型 CT 断层扫描在循环冻融损伤中的见解


了解循环冻融过程中的微观结构演化对于研究循环冻融下混凝土的劣化机制至关重要。在这项研究中，AEA 和聚合物微球将空气夹带到水泥砂浆和浆体中。结合压汞孔隙率测定法 (MIP) 和显微 CT 技术，研究不同冻融循环下标本的微观结构。接受参考号后。将AEA和AEA混合砂浆进行100和200次冻融循环后，从MIP结果观察到孔隙率和孔隙截留增加，表明发生了循环冻融引起的损伤。相反，在微球混合砂浆中，表面吸附水分的存在导致孔隙率和孔隙截留在100次冻融循环后最初增加，随后在200次循环后下降，表明有愈合作用。 Micro-CT分析显示，虽然AEA混合样本的空气含量高于微球混合样本，但后者显示出更多的空隙，这最终增强了其抗冻融能力。显微 CT 结果表明，AEA 混合标本中的气泡往往会合并，从而对其抗冻融能力产生不利影响。相反，掺有微球的样本显示出平滑的空隙分布曲线，表明分布均匀的空气空隙系统增强了其抗冻融性。这项工作表明微球可以成为引气材料的绝佳候选者。结合MIP和显微CT分析可以更好地了解循环冻融混凝土微观结构的变化。