A study to assess oxidative ageing of asphalt concrete using non-collinear wave mixing of two dilatational waves is presented. Criteria were used to assure that the detected scattered wave originated via wave interaction in the asphalt concrete and not from non-linearities in the testing equipment. These criteria included the frequency and propagating direction of the resultant scattered wave and the time-of-flight separation between the two primary waves and the resulting scattered wave. It was observed that asphalt concrete exhibits non-linear behaviour. It was also observed that the non-linear response decreases with increased ageing until approximately 24 h of ageing, after which the non-linear response exponentially increases. This observation is consistent with previous studies, including the acoustic emission response to thermal loading, and with changes in the dynamic modulus and fracture energy with increasing ageing.

/pdf/characterisation-of-oxidative-ageing-in-asphalt-concrete-3bf9e3vv8t.pdf

Characterisation of oxidative ageing in asphalt concrete using a non-collinear ultrasonic wave mixing approach

A study using non-collinear ultrasonic wave mixing of subsurface longitudinal waves for the assessment of oxidative ageing in asphalt concrete samples with increasing levels of oven ageing is presented. The use of subsurface waves allows for non-destructive interrogation of bituminous structures when only one side of the test specimen is available for testing, such as asphalt concrete pavements. The following criteria were used to verify that the non-linear wave originated within the test specimen due to the non-collinear wave mixing, and not from non-linearities inherent to the testing instrumentation: (1) frequency; (2) amplitude; (3) propagation direction; and (4) time-of-flight separation. It was observed that the non-linear response of the asphalt concrete mixtures decreases with ageing until about 24 h of oven ageing, after which it increases exponentially with ageing. These results correlated well with the results from previous studies, demonstrating the effectiveness of this technique. Potential applications of the technique for the health monitoring of asphalt pavement surfaces are presented. M E McGovern, W G Buttlar and H Reis

Estimation of oxidative ageing in asphalt concrete pavements using non-collinear wave mixing of critically-refracted longitudinal waves

While much nonlinear ultrasonics research has been conducted on higher harmonic generation, wave mixing provides the potential for sensitive measurements of incipient damage unencumbered by instrumentation nonlinearity. Studies of nonlinear ultrasonic wave mixing, both collinear and noncollinear, for bulk waves have shown the robust capability of wave mixing for early damage detection. One merit of bulk wave mixing lies in their non-dispersive nature, but guided waves enable inspection of otherwise inaccessible material and a variety of mixing options. Co-directional guided wave mixing was studied previously, but arbitrary direction guided wave mixing has not been addressed until recently. Wave vector analysis is applied to study variable mixing angles to find wave mode triplets (two primary waves and a secondary wave) resulting in the phase matching condition. As a case study, counter-propagating Shear Horizontal (SH) guided wave mixing is analyzed. SH wave interactions generate a secondary Lamb wave mode that is readily receivable. Reception of the secondary Lamb wave mode is compared for an angle beam transducer, an air coupled transducer, and a laser Doppler vibrometer (LDV). Results from the angle beam and air coupled transducers are quite consistent, while the LDV measurement is plagued by variability issues.

Directional nonlinear guided wave mixing: Case study of counter-propagating shear horizontal waves

A method capable of characterizing artificial weathering damage in dimension stone cladding using access to one side only is presented. Dolomitic limestone test samples with increasing levels of damage were created artificially by exposing undamaged samples to increasing temperature levels of 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, and 700°C for a 90 min period of time. Using access to one side only, these test samples were nondestructively evaluated using a nonlinear approach based upon noncollinear wave mixing, which involves mixing two critically refracted dilatational ultrasonic waves. Criteria were used to assure that the detected scattered wave originated via wave interaction in the limestone and not from nonlinearities in the testing equipment. Bending tests were used to evaluate the flexure strength of beam samples extracted from the artificially weathered samples. It was observed that the percentage of strength reduction is linearly correlated ( R 2 = 98 ) with the temperature to which the specimens were exposed; it was noted that samples exposed to 400°C and 600°C had a strength reduction of 60% and 90%, respectively. It was also observed that results from the noncollinear wave mixing approach correlated well ( R 2 = 0.98 ) with the destructively obtained percentage of strength reduction.

Damage characterization in dimension limestone cladding using noncollinear ultrasonic wave mixing

Steering the propagation direction of a non-linear acoustic wave in a solid material.

Characterization of dolomitic limestone rock is presented using linear and nonlinear ultrasonic approaches. The
linear approach is based upon the concept of complex moduli, which is estimated using ultrasonic dilatational and
shear phase velocity measurements and the corresponding attenuations. The nonlinear approach is based upon noncollinear
wave mixing, involving mixing of two dilatational waves. Criteria were used to assure that the detected
scattered wave originated via wave interaction in the limestone and not from nonlinearities in the testing equipment.
These criteria included frequency and propagating direction of the resultant scattered wave, and the time-of-flight
separation between the two primary waves and the resulting scattered wave. Three cases of non-collinear interaction
of two longitudinal waves are presented and discussed including one that requires only access to a plane surface of
the stone test sample.

Henrique L. Reis

Papers

Damage characterization in dimension limestone cladding using noncollinear ultrasonic wave mixing

Linear and nonlinear characterization of limestone rock using a non-collinear ultrasonic wave mixing