Airborne ultrasounds for damaged cementitious characterization

Abstract

[EN] The scope of this paper is to demonstrate the capability of airborne non-contact ultrasound (ANC-US) to assess thermal damage on normalized Portland cement mortar specimens. For this purpose, contact ultrasound (C-US) and ANC-US are compared. A normalized dosage mortar was carried out to obtain standardized mortar specimens of 4 x 4 x 16 cm. Then, they were measured by ANC-US and C-US. Afterwards, they were thermal damaged (400º C) and measured again. Ultrasound velocity and frequency attenuation were estimated. As expected, damaged samples show lower velocities and higher attenuations than sound samples. It is remarkable how the attenuation keeps constant for frequencies below 100 kHz and increases due to the sensitivity of higher frequencies to the size of thermal microcracking. Although ANC-US does not require any coupling media as C-US does, it requires additional calibration to compensate propagation through the air and material boundaries. Considering these terms, both techniques offer consistent results and the capability of ANC-US technique for damage characterization in cementitious systems is proved.