• Ospitia Patino, Nicolas

Abstract

Textile Reinforced Cementitious (TRC) sandwich composites<br/>are innovative construction materials composed of two slender<br/>TRC facings, and a thick thermal and acoustic insulating core.<br/>Their non-corrosive nature allows for slender structures,<br/>resulting in a reduction of the cement used, and therefore a<br/>decrease of the negative impact on the environment. The<br/>sandwich technology brings superior bending resistance while<br/>enforcing the lightweight nature of the composite. Despite the<br/>numerous advantages of TRC sandwich composites, they present<br/>a complex and possibly unpredictable fracture behavior, and<br/>manufacturing issues such as a weak interlaminar bond and<br/>therefore, there is a need for status verification in the different<br/>stages of their service life: at the manufacturing stage (curing),<br/>final product quality (manufacturing defects), deterioration<br/>during use (damage accumulation). There is currently no reliable<br/>non-invasive inspection protocol that assesses the curing of the<br/>cementitious facings, and provides for quality control and<br/>damage monitoring.<br/>Along this study, a combination of Non-Destructive Testing<br/>(NDT) techniques is employed to provide a protocol that allows<br/>monitoring the composite from the hardening of the cementitious<br/>facings, enables quality control, and finally, supports damage<br/>characterization. Electromagnetic millimeter wave (MMW)<br/>spectrometry is employed for the first time in this kind of<br/>material to monitor the hydration of cementitious media, to carry<br/>our quality control, and to characterize damage. Additionally,<br/>passive, and active elastic wave-based NDT techniques, like<br/>Acoustic Emission (AE) and Ultrasound inspection, respectively,<br/>are also used in combination with Digital Image Correlation<br/>(DIC) to characterize the material along its lifetime, and to serve<br/>as a benchmark for MMW spectrometry. This thesis summarizes<br/>the results of an extensive experimental campaign and<br/>highlights the innovative contributions. Previously unknown<br/>relations between electromagnetic properties measured by<br/>MMW and mechanical properties obtained with ultrasound<br/>inspection are revealed due to the hydration reactions that<br/>dictates the permittivity and stiffness development. AE during<br/>proof-loading reveals the effect of manufacturing defects due to<br/>the local stress field variations that they impose under<br/>mechanical tests. In addition, cracking and debonding leave a<br/>strong fingerprint on the electromagnetic transmission, enabling<br/>a multi-spectral methodology for structural health monitoring<br/>(SHM) of such innovative components during their lifetime.

Topics

• impedance spectroscopy
• composite
• cement
• defect
• acoustic emission
• fracture behavior
• spectrometry
• curing