Alkali–silica reaction in concrete structures due to simultaneous cyclic loading and external supply of alkali: Results of the DFG research group FOR 1498
Alkali–silica reaction in concrete structures due to simultaneous cyclic loading and external supply of alkali: Results of the DFG research group FOR 1498
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由于同时循环加载和外部供应碱而导致的混凝土结构中的碱硅反应：DFG 研究小组 FOR 1498 的结果
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发表时间：
2017
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通讯作者：
R. Breitenbücher
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作者：
R. Breitenbücher
混凝土结构中的碱-硅反应（ASR）已经研究了几十年。以前对ASR的研究主要集中在潜在反应性骨料和常规混凝土结构中ASR潜力的整体评估上。然而，对于混凝土路面等特殊条件下影响ASR的因素，目前还没有进行全面的研究。外部供应的碱（如除冰剂）可显著增强ASR。这些水溶液渗透到混凝土的微观结构中。特别是在德国近期混凝土路面高速公路的ASR损伤中，外源碱的供应起到了突出的作用。然而，混凝土路面（高速公路和机场）不仅以除冰溶液的形式受到外部碱的影响，而且经常受到超限交通的负荷。由此产生了微观结构的退化。同样，海上风力发电厂也面临着这样的不利处境。它们暴露在海水中的碱性中，同时由于其运行而承受巨大的循环载荷。因此，这种结构在循环载荷和外部碱供应的持续作用下，特别容易受到ASR的破坏。为了限制具有高度经济意义的损害，已经提出了指导方针。它们主要侧重于选择ASR潜力很小的聚集体。然而，这些准则中的极限值完全是凭经验确定的。虽然已经进行了几项研究，重点是混凝土路面中的ASR，但循环荷载下混凝土微观结构内降解过程的基本相互作用以及外部供应的碱对这种微观结构的渗透行为尚未得到系统的研究。为了从根本上评估相关影响和相互作用，德国研究基金会（DFG）于2011年10月成立了FOR 1498研究小组。五个不同的子项目侧重于混凝土微观结构中降解的开始和进展，外部碱进入微观结构的运输以及ASR凝胶的随后形成的相互作用。这些研究考虑了微观层面（骨料颗粒）、中观层面（混凝土基质）和宏观层面（结构，例如混凝土路面板）的过程。
Alkali–silica reaction (ASR) in concrete structures has been known for several decades. Previous investigations of ASR focused mainly on potentially reactive aggregates and the global assessment of the ASR potential in conventional concrete structures. However, comprehensive studies on the influences affecting ASR under special conditions, such as in concrete pavements, have not been performed yet. ASR can significantly be intensified by externally supplied alkalis such as de-icing agents. These aqueous solutions penetrate into the concrete microstructure. Especially in recent ASR damages on highways with concrete pavements in Germany, the external supply of alkalis played a prominent role. Concrete pavements (highways and airports), however, are not only subjected to external alkalis in the form of deicing solutions but are also frequently loaded by overrunning traffic. By those, a microstructural degradation is generated. In the same manner, offshore wind-energy plants are also exposed to such a disadvantageous situation. They are exposed to alkalis in the seawater and simultaneously experience massive cyclic loading due to their operation. Thus, such structures, continuously loaded with cyclic loads and an external alkali supply, are particularly susceptible to a damaging ASR. In an effort to limit the damages, which are of high economic relevance, guidelines have been introduced. They mainly focus on the selection of aggregates with only little ASR potential. However, the limit values in these guidelines had been defined solely empirically. Although, several studies had been performed focusing on ASR in concrete pavements, the fundamental interactions of degradation processes within the concrete’s microstructure under cyclic loadings and the penetration behavior of externally supplied alkalis into such a microstructure have not been investigated systematically. In an effort to assess the relevant effects and interactions fundamentally, the research group FOR 1498 was established in October 2011 by the German Research Foundation (DFG). Five different subprojects focus on the interactions of initiation and progress of degradation within the concrete’s microstructure, the transport of external alkalis into the microstructure as well as the subsequent formation of ASR gel. These studies consider the processes at the microlevel (aggregate grains), the mesolevel (concrete matrix), and finally at the macrolevel (structure, e.g., concrete pavement slabs).