Environmentally/mechanically caused changes in microstructure and their effect on coda signals

尾波干涉法（CWI）特别适用于钢筋混凝土（RC）结构的长期评估。该项目的目标是开发和理解Coda技术作为评估RC结构完整性和耐久性的工具。通过可控的一维实验，本子项目旨在确定机械载荷和环境影响对Coda信号的影响。一方面，建立由直接撞击引起的尾线扰动的标定曲线。另一方面，典型的混凝土现象，如长期过程碳化或霜冻，将在时域上表征。在项目结束时，将提供一整套校准曲线和具体特征，以便在实际工程结构中进行校准和信号补偿。为了验证信号扰动的来源，使用传统和创新技术表征混凝土微观结构的变化。冲击与微观结构变化之间的关系，以及对Coda信号的相应分析和解释，为模拟波传播、材料特性和结构变化提供了重要的输入参数，因为它们是在本研究单元的其他个别项目范围内开发的。在该项目的第二阶段，通过试样几何形状、表面状况和加固的影响，系统地扩展了第一阶段一维测试的关系，所有这些都与尾轴的相应变化有关。此外，实际相关的湿度和温度梯度将在均匀状态表征后进行研究。通过验证方法计算机断层扫描，声发射和薄片显微镜，将特别关注微观结构水平上可逆和不可逆变化的扰动之间的分离。此外，研究组还计划在连接乌尔姆和新乌尔姆的Gänstorbrücke和慕尼黑的Scheidplatz地铁站两个工程结构上进行CWI监测基准试验。TUM1将负责协调Scheidplatz的仪器，以及准备和维护有关公共数据库的数据采集。通过该项目，将为CWI方法在现代建筑技术和我们的建筑环境中的许多应用提供基础。

Coda Wave Interferometry (CWI) is particularly suitable for the long-term assessment of reinforced concrete (RC) structures.The objective of this project is to develop and understand the Coda technique as a tool for assessing the structural integrity and durability of RC structures. Using well-controllable one-dimensional experiments, this subproject aims to determine the effect of mechanical load and environmental impacts on the Coda signal. On the one hand, calibration curves for the perturbation of the Coda because of direct impacts will be established. On the other hand, typical concrete phenomena, e.g. the long-term processes carbonation or frost attack, will be characterized in the time domain. At the end of the project, an entire spectrum of calibration curves and concrete-specific features will be provided to enable calibration and signal compensation at real engineering structures.In order to validate the origin of signal perturbations, changes in concrete microstructure are characterized using conventional and innovative techniques. The relationships between impacts and microstructural changes, together with the corresponding analysis and interpretation of the Coda signals, provide important input parameters for modelling wave propagation, material properties and structural changes as they are developed within the scope of other individual projects within this research unit.During the second phase of this project, relationships from one-dimensional tests from the first phase are extended systematically by the effect of specimen geometry, surface condition, and reinforcement, all related to the corresponding changes in the Coda. In addition, practically relevant moisture and temperature gradients will be investigated following the characterization of homogeneous states. Special focus will be put into the separation between perturbations from reversible compared to irreversible changes on the micro structural level by means of the validating methods computed tomography, acoustic emission, and thin section microscopy.Furthermore, the research unit intends to conduct benchmark tests for CWI monitoring at two engineering structures, the Gänstorbrücke, which connects Ulm and Neu-Ulm, and the underground station Scheidplatz in Munich. TUM1 will take responsibility for the coordination of the instrumentation of the Scheidplatz as well as the preparation and maintenance regarding data acquisition to a common database.With this project, the basis for many applications of the CWI method in modern construction technology and our built environment will be provided.