Ilker Boz

The Effect of Aspect Ratio on the Frequency Response of Asphalt Concrete in Impact Resonance Testing

A comprehensive study was conducted to investigate the influence of aspect ratio (height/diameter) of laboratory specimens on the frequency response of asphalt concrete when tested with impact resonance (IR). Testing was conducted over a range of air voids and temperatures. The IR test, performed in longitudinal mode over 100 cylindrical asphalt concrete specimens, demonstrated that the test is repeatable and reproducible. It was observed that the test response was greatly dependent on the specimen length regardless of the aspect ratio, but the dependency was not noted for specimens with the same diameter of larger aspect ratios. Specimens with the same aspect ratio but different size delivered different resonant frequencies. The test results indicated that the frequency response increased as the aspect ratio increased approximately up to 0.7, and then it decreased with a nonlinear trend as the aspect ratio increased beyond 0.7, indicating the tendency of the frequency response reaching a plateau as the aspect ratio increased. It was inferred from test results that there was a threshold aspect ratio at which the fundamental longitudinal frequency mode was not the dominant frequency mode. Velocity calculations from measured resonant frequencies indicated that the true material properties could be attained at an aspect ratio of as low as 1. Based on the results of this study, testing specimens with a diameter of 150 mm and a height of 170 mm commonly used for producing dynamic modulus test specimens, provided proper size and aspect ratio for testing with IR.

Investigating the effect of rejuvenators on low-temperature properties of recycled asphalt using impact resonance test

ABSTRACT Use of recycled asphalt pavement (RAP) in highway construction is highly promoted due to recent awareness in sustainable construction practices. The concerns with material brittleness in utilising higher content of RAP are alleviated through addition of rejuvenators to some extent. Inclusion of rejuvenator to the aged binder improves its flexibility and lessens its cracking potential. A study was undertaken to investigate the effectiveness of the impact resonance (IR) testing in determining low-temperature binder properties through mixture testing. To this effect, the presented study consisted of two stages. In stage I, the IR test was conducted on mixes made with different low-temperature grade binders. Stage II consisted of testing pure RAP mixes treated with a rejuvenating agent at different levels using the IR as well as testing blends of recovered RAP binder and rejuvenator and virgin binder using bending beam rheometer (BBR). The IR test was performed at a range of temperatures between and . The results indicate that the IR test can successfully capture the low-temperature properties of binders in virgin mixes as well as RAP mixes incorporating rejuvenator. A very high linear correlation was observed between stiffness from IR testing of the RAP mix and stiffness from BBR testing of the blend of recovered binder and virgin binder and rejuvenator. A good correlation was also observed between phase angle of RAP mixes obtained from IR with the m-value, a relaxation index, from BBR at a range of temperatures for a given rejuvenator content. The results clearly demonstrate the potential of IR to be used for grading and optimisation for the asphalt binder of RAP and rejuvenator content in lieu of the binder recovery method.

Evaluation of Nondestructiveness of Resonant Column Testing for Characterization of Asphalt Concrete Properties

The resonant column (RC) test has been used as a nondestructive test (NDT) to study dynamic properties of soils for the past few decades. With some modifications, this test can also be employed to characterize properties of asphalt concrete, especially because these properties are strongly dependent on the loading frequency. A conventional RC apparatus was retrofitted to characterize asphalt concrete properties at a range of temperatures from 10°C to 45°C. The RC test is believed to be nondestructive for most soils; however, this must be verified in case of testing asphalt concrete, especially at elevated temperatures. For this purpose, the impact resonance (IR) test, as a purely NDT tool, was used to check the integrity of asphalt concrete specimens before and after RC testing. The modulus values measured before and after RC tests, at each of the testing temperatures, were compared to evaluate the nondestructiveness of RC testing. Strain levels were also monitored to ensure that the material remained within the linear elastic range through the tests. The results show that the specimens exhibited the same modulus before and after RC testing over the full range of temperature and frequency sweep tests.