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- Bekele, Abiy, 1983-
(författare)
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Application of Automated Non-contact Resonance Testing for Low Temperature Behavior of Asphalt Concrete
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Impact resonance testing is a well-documented non-destructive testing method and its applications on asphalt concrete have also been implemented successfully. The test is carried out manually by inducing an impact in order to excite the test specimen and taking measurements of the vibrational response. In an effort to improve the manual procedure of impact resonance testing, an automated non-contact methodology is developed and its applicability with regards to low temperature behaviors of asphalt concrete is investigated. Results from this work show that repeatable fundamental resonance frequency measurements can be performed on a disc shaped specimen in an automated manner without the need to open the thermal chamber. The measurements obtained from the new method have been verified by taking similar resonance frequency measurements using an instrumented impact hammer. It has also been shown in this work that the proposed method is suitable to investigate the lone effects of cyclic thermal conditioning on asphalt concrete without any other possible biasing effects associated with contact in the conventional testing. A hysteretic behavior of stiffness modulus is obtained on three different asphalt concrete specimens subjected to repeated low temperature cyclic conditioning. Reduced modulus values at each temperature are obtained in all the tested specimens after a low temperature stepwise conditioning at temperatures from 0oC to -40 oC. This observed behavior shows that the dynamic modulus of the tested specimens is affected by low temperature conditioning. The norm of the complex modulus decreases and the phase angle or damping ratio increases after low temperature conditioning. Hence, valuable and practical low temperature characteristics of different asphalt concrete mixtures can possibly be obtained by using the proposed methodology.
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| 2. |
- Bekele, Abiy, 1983-
(författare)
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Automated Non-contact Resonance Excitation Method for Low Temperature Behavior of Asphalt Concrete
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper studies the applicability of an automated non-destructivetesting method to monitor the stiffness of asphalt concrete at lowtemperatures. A loudspeaker is used as a source of non-contact excitation ofthe axially symmetric fundamental resonance frequencies of a disc-shapedasphalt concrete specimen positioned inside an environmental chamber. Measuredresonance frequencies are used to calculate the dynamic moduli of the specimenat different temperatures. The repeatability of the method as well as theeffect of loudspeaker height above the sample are studied. Results show thatthe main advantage of the non-contact excitation method, compared to manuallyapplied impact hammer excitation, is that repeatable automated measurements canbe performed while the specimen is placed inside an environmental temperaturechamber. This methodology enables to study the effect of only low temperatureconditioning on the dynamic modulus of asphalt concrete without interferencefrom mechanical loading.
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| 3. |
- Bekele, Abiy, 1983-
(författare)
-
Effect of Cyclic low temperature conditioning on Stiffness Modulus of Asphalt Concrete based on Non-contact Resonance testing method
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The stiffness modulus behaviors of three different asphalt concrete specimens that are subjected to cyclic cooling and heating are monitored. In an attempt to identify the sole effect of temperature cycles and to avoid any other biasing effects such as thermal contamination that can possibly corrupt measurements, resonance frequency measurements of the specimens are taken using an automated non-contact resonance method. The resonance frequency measurements are based on the fundamental axially symmetric mode of vibration. A hysteretic effect is observed on the measured resonance frequencies of the specimens with an application of cyclic cooling and heating. Lower stiffness moduli are obtained during the heating phase of a complete cooling and heating cycle. The stiffness moduli are calculated from measured resonance frequencies of the specimens in order to show their relative reductions due to the hysteretic effect. This finding is particularly important since it enables us to observe and understand the effect of the thermal history of asphalt concrete with regards to the reversibility behavior of its stiffness modulus. The damping of the specimens is also calculated from the measured resonance frequencies at the temperatures within the applied cyclic cooling and heating. Their observed behavior is also discussed with respect to a presence of potential micro damage.
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