Unravelling textile-reinforced cementitious composites by means of multimodal sensing techniques

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.