Externer Alkalieintrag in mechanisch/thermisch vorgeschädigtes Betongefüge

在主要以实验为导向的子项目TP 1中，循环荷载引起的降解及其对外部供应的碱进入混凝土微观结构的运输机制的影响是调查的重点。考虑到由于混凝土内的实际循环交通和约束应力导致的退化，将在各种应力水平和各种荷载循环次数下对大型混凝土梁进行测试。通过测量梁表面的超声波运行时间来描述混凝土微观结构内部的变化。循环加载后，在显微切片上确定了相关的裂纹参数，如长度、宽度和裂纹数。因此，可以量化预损伤的程度。这些参数表征了降解并验证了数值模型（来自TP 3）。通常，微观组织退化不会导致疲劳失效。然而，它在很大程度上影响了外部供应的碱进入混凝土的传输机制。子项目TP 1中的预损坏试样中的液体渗透行为将通过评估压力下的吸水率以及毛细作用来确定。因此，根据预损伤的程度，可以评估对液体/碱渗透的影响，以验证数值模型。此外，还将在改进的迁移池中评估ASR相关Na离子的渗透行为。在子项目TP 1中，还将通过实验评估超滚轮胎对外部供应的碱的渗透行为的影响。因此，未受损伤以及预损坏的混凝土梁将用加载轮胎覆盖;同时在表面上施加NaCl溶液。在达到所需的过卷次数后，将评估碱的渗透深度。因此，可以定义预损伤程度与穿透深度之间的直接相关性。总之，将采集的标本样本储存在ASR激发环境中，并评估取决于降解和外部碱供应的ASR菌株潜力。在第一个供资期，重点是关于循环载荷引起的降解和液体渗透行为的调查。在第二个供资期内，将特别评估外部供应的碱通过过滚轮胎的渗透，并最终评估由此产生的ASR。通过对子项目TP 4（3D-CT、LIBS）、TP 5（KWL）和TP 6（三维机械参数）中的其他参数进行评估，将对TP 1中获得的结果进行补充。此外，子项目TP 3和TP 6的相应数值模型将通过TP 1的实验获得的结果进行验证。

Within the predominantly experimentally orientated sub-project TP1 the degradation induced by cyclic loading as well as its effects on the transport mechanisms of externally supplied alkalis into the con-crete microstructure are in the focus of the investigations. Regarding degradation due to realistic su-perposed cyclic traffic and restraint stresses within the concrete, large concrete beams will be tested under various stress levels and various numbers of load cycles. The changes within the concrete mi-crostructure will be described by measurement of the ultrasonic runtimes on the surface of the beam. After the cyclic loadings the relevant crack parameters as length, width, and crack numbers are de-termined on microsections. Thus, the degree of pre-damaging can be quantified. These parameters characterize the degradation and validate the numerical models (from TP3). Generally, the microstruc-tural degradation does not lead to fatigue failure. Nevertheless, it affects the transport mechanisms of i.e. externally supplied alkalis into the concrete largely. The penetration behavior of liquids in pre-damaged specimen in sub-project TP1, will be determined through the evaluation of the water uptake under pressure as well as capillary suiction. Thus, in dependence of the degree of pre-damaging, the effect on the penetration of liquids/alkalis can be assessed for validation the numerical models. Fur-ther, the penetration behavior of ASRrelevant Na-ions will be evaluated in a modified migration cell. The effect of an overrolling tire on the penetration behavior of externally supplied alkalis will be also experimentally assessed in sub-project TP1. Therefore, unoffended as well as pre-damaged concrete beams will be overrolled with a loaded tire; simultaneously a NaCl-solution is applied on the surface. After the desired number of overrollings the penetration depth of alkalis will be evaluated. Thus, a direct correlation between the degree of pre-damaging and the penetration depth can be defined. Conclusively, the acquired specimen samples will be stored in an ASR-provoking environment and the ASR-strain-potential depending on the degradation and the external alkali supply will be assessed. In the first funding period the focus lay on the investigations regarding the degradation caused by cyclic loading and the penetration behavior of liquids. In the second funding period especially the penetration of externally supplied alkalis by an overrolling tire and ultimately the resulting ASR will be assessed. Through the assessment of further parameters in the sub-projects TP4 (3D-CT, LIBS), TP5 (KWL) and TP6 (fracture-mechanical parameters) the results acquired in TP1 will be complemented beneficiary. Furthermore, corresponding numerical model from the sub-projects TP3 and TP6 will be validated through the experimentally acquired results from TP1.