Abstract
Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.
Highlights
IntroductionThe B- and C-scans operated in time domain are unable to study the frequency features of the time-varying Ground penetrating radar (GPR) signals, which are largely affected by the spatial or temporal changes of the concrete properties
The study was experimented by measuring the changes of Ground penetrating radar (GPR) A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone
The bar reflections were ill defined in time domain from the fresh state to day 4 because high water content caused more attenuation suffered by the high-frequency GPR antennae
Summary
The B- and C-scans operated in time domain are unable to study the frequency features of the time-varying GPR signals, which are largely affected by the spatial or temporal changes of the concrete properties. In other words, when the interpretation of GPR signals is extended from object’s location and spatial characterization to the study of material properties, the time domain method may not be adequate because the characteristic of the time-varying frequency is not taken into account. The A-scans were processed and transformed to 2D time-frequency plots to observe the lateral frequency changes for both direct wave and an embedded steel bar reflector These signals were further characterized and quantified by determination of the peak frequency, and justified by the dielectric relaxation and OPC hydration theories
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
