Diagnosing delayed ettringite formation in concrete structures
Diagnosing delayed ettringite formation in concrete structures
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DOI：
10.1016/j.cemconres.2008.01.003
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发表时间：
2008-06-01
影响因子：
11.4
通讯作者：
Ramlochan, Terry
中科院分区：
文献类型：
--
作者：
Thomas, Michael;Folliard, Kevin;Ramlochan, Terry
在北美，已经有许多涉及混凝土结构劣化的案例，其中围绕碱-硅反应（ASR）和延迟钙矾石形成（DEF）对所观察到的损坏的各自贡献存在相当大的争议。出现的问题，因为宏观症状的困扰是不明确的和显微镜检查的现场样品往往揭示了这两个过程的证据，使其难以分开的个人贡献。本文介绍了一些混凝土柱进行了提高高速公路在北美的调查结果，以前的研究都涉及DEF和ASR恶化的可能原因。虽然这些柱子没有被故意加热固化，但据估计，内部温度峰值将超过70摄氏度，在某些情况下甚至可能超过80摄氏度。法医调查包括扫描电子显微镜和能量分散X射线分析，以及对从建筑物中提取的岩芯进行膨胀测试。储存在石灰水中的小直径芯材显著膨胀（0.3%至1.3%），根据对实验室生产的混凝土试样进行的补充试验得出结论，在这种条件下的膨胀是由DEF引起的，因为试验条件不会维持ASR。在至少一列中，DEF被诊断为损坏的唯一原因，没有证据表明ASR或任何其他恶化过程有任何贡献。在其他情况下，观察到ASR和DEF都导致了明显的损伤。在检查的柱子中，只有含有粉煤灰的混凝土似乎没有损坏。本研究的结果证实，在某些条件下，DEF的过程（在其他过程中的隔离作用）可以导致显着恶化的现浇钢筋混凝土结构。(C)2008爱思唯尔有限公司保留所有权利。
There has been a number of cases involving deteriorated concrete structures in North America where there has been considerable controversy surrounding the respective contributions of alkali-silica reaction (ASR) and delayed ettringite formation (DEF) to the observed damage. The problem arises because the macroscopic symptoms of distress are not unequivocal and microscopical examinations of field samples often reveal evidence of both processes making it difficult to separate the individual contributions. This paper presents the results of an investigation of a number of concrete columns carrying a raised expressway in North America; prior studies had implicated both DEF and ASR as possible causes of deterioration. Although the columns were not deliberately heat-cured, it is estimated that the peak internal temperature would have exceeded 70 degrees C and perhaps even 80 degrees C, in some cases. The forensic investigation included scanning electron microscopy with energy-dispersive X-ray analysis and expansion testing of cores extracted from the structure. Small-diameter cores stored in limewater expanded significantly (0.3 to 1.3%) and on the basis of supplementary tests on laboratory-produced concrete specimens it was concluded that expansion under such conditions is caused by DEF as the conditions of the test will not sustain ASR. In at least one column, DEF was diagnosed as the sole contributory cause of damage with no evidence of any contribution from ASR or any other deterioration process. In other cases, both ASR and DEF were observed to have contributed to the apparent damage. Of the columns examined, only concrete containing fly ash appeared to be undamaged. The results of this study confirm that, under certain conditions, the process of DEF (acting in isolation of other processes) can result in significant deterioration of cast-in-place reinforced concrete structures. (C) 2008 Elsevier Ltd. All rights reserved.