The ultrasonic pulse velocity, obtained by ultrasonic non-destructive testing, has been applied to evaluate the concrete integrity. The attenuation parameters have shown more sensitivity to damage detection in the microstructure of concrete since they consider the entire ultrasonic waveform. However, it is still necessary to evaluate the sensitivity of those parameters to thermally damaged concrete. This work aims to assess the behavior and the sensitivity of the following ultrasonic parameters: pulse and group velocities, maximum amplitude, total energy, accumulated energy, and time instants corresponding to 25%, 50%, and 75% of the energy, in detecting changes due to thermal degradation of the concrete. A sample of 39 cylindrical concrete specimens with 100 mm in diameter and 300 mm in length and C25 strength class was used. The sample was distributed into 5 groups heated between 20 and 400 ºC until the internal temperature of the specimens became homogeneous. The groups were cooled inside a muffle furnace until reaching 150 ºC. Subsequently, they were exposed to the ambient temperature and humidity of the laboratory environment for, at least, 24 hours prior to the tests of mass loss, ultrasound, and compressive strength. The results show that the ultrasonic parameters are sensitive to the thermal degradation of the concrete. The pulse velocity, the accumulated energy, and the time instants corresponding to percentages of the energy decrease monotonically as the temperature increases. The group velocity shows significant dispersions, while the maximum amplitude and the total energy increase at 200 ºC. The results led to the conclusion that the pulse velocity is the least sensitive parameter, while the time instants corresponding to 25%, 50%, and 75% of the energy are the most sensitive parameters in detecting changes due to thermal degradation of the concrete.

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<p>Neste trabalho são apresentadas as características e a resistência ao cisalhamento das interfaces soldadas por fricção rotativa (SFR) de cavilhas de madeira de itaúba em substratos de madeira de pinus. Os corpos de prova são compostos por cavilhas de itaúba e substratos de pinus, nos quais foram usinados pré-furos usando duas relações de diâmetro cavilha/pré-furo: 1,25 e 1,11. Após a SFR, as uniões soldadas foram submetidas a ensaios mecânicos de extração das cavilhas, a fim de se determinar a tensão de cisalhamento na ruptura. A macro e a microestrutura da interface soldada foram avaliadas visualmente e por microscopia eletrônica de varredura (MEV). Os resultados mostram que: a tensão de cisalhamento média na ruptura, para as relações diâmetro cavilha/pré-furo de 1,25 e 1,11, são de 2,41 e 1,77 MPa, respectivamente, indicando que, para as madeiras estudadas, a relação diâmetro cavilha/pré-furo de 1,25 apresenta ligações soldadas mais resistentes; a SFR ocasiona o escurecimento da interface de soldagem; o pré-furo e a cavilha, originalmente cilíndricos, assumem um formato cônico, durante o processo de SFR; a interface entre as madeiras de pinus e de itaúba é homogênea e bem soldada.</p>

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