Ospitia Nicolas, Pourkazemi Ali, Tsangouri Eleni, Tayeh Thaer, Stiens Johan H, Aggelis Dimitrios G
Department of Mechanics of Materials and Constructions, Faculty of Engineering, Vrije Universiteit Brussel, B-1050 Brussels, Belgium.
Magnel-Vandepitte Laboratory, Department of Structural Engineering and Building Materials, Faculty of Engineering and Architecture, Ghent University, B-9052 Gent, Belgium.
Materials (Basel). 2024 Dec 20;17(24):6232. doi: 10.3390/ma17246232.
Cementitious materials are susceptible to damage not only from mechanical loading, but also from environmental (physical, chemical, and biological) factors. For Textile-Reinforced Cementitious (TRC) composites, durability poses a significant challenge, and a reliable method to assess long-term performance is still lacking. Among various durability attacks, freeze-thaw can induce internal cracking within the cementitious matrix, and weaken the textile-matrix bond. Such cracks result from hydraulic, osmotic, and crystallization pressure arising from the thermal cycles, leading to a reduction in the stiffness in the TRC composites. Early detection of freeze-thaw deterioration can significantly reduce the cost of repair, which is only possible through periodic, full-field monitoring of the composite. Full-field monitoring provides a comprehensive view of the damage distribution, offering valuable insights into the causes and progression of damage. The crack location, size, and pattern give more information than that offered by single-point measurement. While visual inspections are commonly employed for crack assessment, they are often time-consuming. Technological advances now enable crack pattern classification based on high-quality surface images; however, these methods only provide information limited to the surface. Elastic wave-based non-destructive testing (NDT) methods are highly sensitive to the material's mechanical properties, and therefore are widely used for damage monitoring. On the other hand, electromagnetic wave-based NDTs offer the advantage of fast, non-contact measurements. Micro- and millimeter wave frequencies offer a balance of high resolution and wave penetration, although they have not yet been sufficiently explored for detecting damage in cementitious composites. In this study, TRC specimens were subjected to up to 150 freeze-thaw cycles and monitored using a combination of active elastic and electromagnetic wave-based NDT mapping methods. For this purpose, transmission measurements were conducted at multiple points, with ultrasonic pulse velocity (UPV) employed as a benchmark and, for the first time, millimeter wave (MMW) spectrometry applied. This multi-modal mapping approach enabled the tracking of damage progression, and the identification of degraded zones.
胶凝材料不仅容易受到机械载荷的破坏，还容易受到环境（物理、化学和生物）因素的影响。对于纺织增强胶凝（TRC）复合材料来说，耐久性是一个重大挑战，目前仍缺乏一种可靠的方法来评估其长期性能。在各种耐久性破坏中，冻融循环会导致胶凝基体内部产生裂缝，并削弱织物与基体之间的粘结力。这些裂缝是由热循环产生的水力、渗透和结晶压力引起的，导致TRC复合材料的刚度降低。早期检测冻融破坏可以显著降低修复成本，而这只有通过对复合材料进行定期的全场监测才能实现。全场监测可以全面了解损伤分布情况，为损伤的原因和发展提供有价值的见解。裂缝的位置、大小和形态提供的信息比单点测量更多。虽然目视检查通常用于裂缝评估，但往往耗时较长。现在的技术进步使得基于高质量表面图像的裂缝模式分类成为可能；然而，这些方法只提供限于表面的信息。基于弹性波的无损检测（NDT）方法对材料的机械性能高度敏感，因此被广泛用于损伤监测。另一方面，基于电磁波的无损检测具有快速、非接触测量的优势。微波和毫米波频率在高分辨率和波穿透性之间取得了平衡，尽管它们在检测胶凝复合材料损伤方面尚未得到充分探索。在本研究中，TRC试件经受了多达150次冻融循环，并使用基于主动弹性和电磁波的无损检测映射方法相结合进行监测。为此，在多个点进行了透射测量，以超声波脉冲速度（UPV）作为基准，并首次应用毫米波（MMW）光谱法。这种多模态映射方法能够跟踪损伤的发展，并识别退化区域。
