Abstract Polymeric composites absorb measurable amounts of moisture from their environment in almost all operating conditions. This absorbed moisture exists either in the “free” state, without any interactions, or in the “bound” state—interacting with the polymer matrix via secondary bonding mechanisms. The ratio and distribution of these water states within a moisture‐contaminated polymer composite are sensitive to physical damage. However, the water state distribution is also affected by variations in total water content resulting from humidity or precipitation‐driven fluctuations in the ambient environment, which could confound the ability to detect damage within the polymer matrix using this technique. To understand the effect of moisture content variations on water state distribution, low levels of barely visible impact damage were induced in epoxy/glass fiber composites. Spatial variations in polymer–water interactions were identified by their characteristic dielectric properties, measured using a split post dielectric resonator operating at 5 GHz. Gravimetric moisture uptake and relative permittivity were monitored during the absorption and desorption processes. Results indicate moisture absorption/desorption history has a significant effect on the sensitivity of damage detection using water state variations. Damage‐dependent hysteresis was observed in relative permittivity, highlighting an avenue by which the confounding effects of moisture absorption/desorption history may be mitigated.
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Microwave materials characterization of geopolymer precursor powders
Geopolymers are structural materials that can be used as a viable alternative to ordinary portland cement concrete. However, their widespread adoption has been limited by the lack of understanding in their fundamental reaction mechanisms. Microwave characterization methods have shown promise at understanding these reaction mechanisms. However, the complex dielectric properties of geopolymer precursor powders and the effect of void content must first be understood. Therefore, in this work, the dielectric properties of two geopolymer precursor powders (blast furnace slag and fly ash) are measured. Then, the effect of void content and particle size distribution (PSD) is considered on the measured dielectric properties. By characterizing the inherent void content of these powder materials, this effect can be removed and therefore the true dielectric properties of the materials can be determined. The results show that the void content has a significant effect on the measured dielectric properties.
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- Award ID(s):
- 1663646
- PAR ID:
- 10099995
- Date Published:
- Journal Name:
- 2018 IEEE International Instrumentation and Measurement Technology Conference (I2MTC)
- Page Range / eLocation ID:
- 1 to 5
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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