Publication Details
Nicolas Ospitia



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