Investigation on possible causes of expansion damages in concrete
Investigation on possible causes of expansion damages in concrete
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混凝土膨胀损伤可能原因的探讨
DOI：
10.18702/acf.2017.06.3.1.49
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发表时间：
2017
影响因子：
11.4
通讯作者：
S. Goto
中科院分区：
文献类型：
--
作者：
Anupam Awasthi;Koji Matsumoto;K. Nagai;S. Asamoto;S. Goto
印度铁路公司使用工厂制造的预张预应力混凝土轨枕。在印度铁路的许多地区，这些轨枕在制造6-9年后开始开裂。为了调查轨枕的过早开裂，从印度铁路的不同地点收集了不同类别的样本，即“严重损坏”、“中度损坏”和“未损坏”样本。在扫描电子显微镜（SEM）和能量色散谱（EDS）下分析这些样品。SEM图像显示，有大量的钙矾石沉积在骨料和糊状物的界面处的情况下，“严重损坏”和“中度损坏”的轨枕，这可能是有害的膨胀和随后的开裂的原因，而“未损坏”的轨枕的接口被发现是完整的。这些轨枕在工厂生产过程中以蒸汽养护的形式经历的高温可能导致延迟钙矾石形成（DEF）以及随后的膨胀和开裂。在轨枕蒸汽处理期间，混凝土轨枕厂记录的温度显示，混凝土内部温度超过80°C，这是将来由于DEF而发生损坏的临界温度。此外，印度铁路公司在旧混凝土轨枕厂使用的生产混凝土轨枕的应力台方法存在一些结构缺陷，对固化温度产生不利影响。因此，DEF可能是印度铁路轨枕过早开裂的原因。
Indian Railways uses factory made pre-tensioned pre-stressed concrete sleepers for its track. These sleepers start cracking after 6-9 years of their manufacturing in many areas of the Indian Railways. For the investigation of the premature cracking of sleepers, different categories of samples namely “Severely damaged”, “Moderately damaged”, and “Undamaged” are collected from different locations of Indian Railways. These samples are analyzed under Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS). SEM images reveal that there is large ettringite deposition at the interfaces of aggregate and paste in case of “Severely damaged” and “Moderately damaged” sleepers, which could be a cause of deleterious expansion and subsequent cracking, whereas the interfaces of “Undamaged” sleepers were found to be intact. High temperature experienced by these sleepers in form of steam curing during their production in factories may lead to Delayed Ettringite Formation (DEF) and subsequent expansion and cracking. Temperature recorded in the concrete sleeper plant during steaming of the sleepers reveals that the temperature inside concrete exceeds 80°C, which is a critical temperature for the occurrence of damage due to DEF in future. Also, stress bench method of production of concrete sleepers, used in Indian Railways for older concrete sleeper plant, poses some structural deficiency which adversely affects the temperature of curing. Thus, DEF could be the possible cause of premature cracking of sleepers in Indian Railways.