Water-induced damage mechanisms of cyclic loaded high-performance concretes

循环荷载高性能混凝土的水致损伤机制

• 批准号: 353757395
• 负责人: Professor Dr.-Ing. Michael Haist
• 金额: --
• 依托单位: Institut für Baumechanik und Numerische Mechanik (IBNM)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/353757395?language=en
• 关键词: Water; induced; damage; mechanisms; cyclic

The expansion of offshore wind energy systems is causing the number of concrete structures which experience loading cycles in excess of several 10^8 while constantly interacting with water to increase. During the first funding period (FP I) a water-induced “saturation damage” (occurring during load decrease) was unmistakeably distinguished from an atmospheric fatigue damage mechanism (above average load) by acoustic emission measurements (Lohaus). Additionally, it was demonstrated by way of NMR-investigations that damage effects correlate with water relocations within the nano-porous system of the hardened cement paste (Haist). Own numerical developments also clearly demonstrated the difference in the degradation behaviour between dry and saturated concrete in the meantime (Wriggers/Aldakheel).In spite of these advancements a detailed understanding of the underlying mechanisms is still lacking. The effects to be described occur at such minute scales that further investigations in the experimental and numerical portions are being more strongly oriented towards measurement of nanoscopic effects. The modelling of failure mechanisms must be further refined in order to account for the complex properties of the microstructure, such as the creation, the growth and the coalescence of pores.The objective of FP II is to quantify, better comprehend, describe and model the mechanism of “saturation damaging” during fatigue failure of concrete, building on the modelling approaches developed during FP I. For this purpose, the different types of fatigue damage in “dry” and “moist” conditions must first be differentiated from one another using the analysis of acoustic emission occurrences. Further the influencing parameters such as loading frequency or damage existing prior to loading must be quantified. In order to better understand the mechanisms at work, water redistribution processes within the pore system on the nanoscopic and microscopic scales will be investigated and resulting microstructural damages and changes in the mechanical properties of the hardened cement paste and mortar will be detected, which may then be translated into a simplified analytical engineering model. Finally, damage processes occurring at nanoscopic scale are to be modelled at the microstructural level by way of adequate homogenisation techniques. This model is intended also to portray the damage evolution with help of cycle-jump-techniques, so that finally the water-induced fatigue damage of concrete may be completely numerically depicted and predicted.With the developed methods the description of the degradation behaviour of fatigue loaded high-performance concrete under water on the basis of microstructural parameters will become possible for the first time in the Experimental-Virtual-Lab.

海上风能系统的扩展导致混凝土结构的数量增加，这些结构在不断与水相互作用的同时经历超过几十个10^8的荷载循环。在第一个资助期间（FP I），通过声发射测量（Lohaus）将水引起的“饱和损伤”（在载荷降低期间发生）与大气疲劳损伤机制（高于平均载荷）明确区分开来。此外，它被证明通过核磁共振研究的方式，损害效应与硬化水泥浆（Haist）的纳米多孔系统内的水迁移。自己的数值发展也清楚地表明了干燥和饱和混凝土之间的退化行为的差异，同时（Wriggers/Aldakheel）。尽管有这些进步，但仍然缺乏对潜在机制的详细了解。要描述的效果发生在这样的微小尺度，在实验和数值部分的进一步调查正在更强烈地面向纳米效应的测量。破坏机制的建模必须进一步完善，以解释微观结构的复杂特性，如孔隙的产生、生长和合并。FP II的目标是量化、更好地理解、描述和建模混凝土疲劳破坏过程中的“饱和破坏”机制，建立在FP I期间开发的建模方法基础上。为此，必须首先使用声发射事件的分析来区分“干燥”和“潮湿”条件下的不同类型的疲劳损伤。此外，必须量化影响参数，如加载频率或加载前存在的损伤。为了更好地理解工作机制，将研究纳米和微观尺度上孔隙系统内的水再分布过程，并检测硬化水泥浆和砂浆的微观结构损伤和机械性能变化，然后将其转化为简化的分析工程模型。最后，在纳米尺度上发生的损伤过程将在微观结构水平上通过适当的均匀化技术进行建模。该模型还打算描绘的损伤演化的帮助下，循环跳跃技术，使最终的混凝土的水致疲劳损伤可以完全数值描述和predicted.With开发的方法的疲劳加载的高性能混凝土在水中的微观结构参数的基础上的退化行为的描述将成为可能的第一次在实验虚拟实验室。