Investigation of Physical and Microstructural Changes in the Surface of Mortar Samples Exposed to Sulphuric Acid

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Title: Investigation of Physical and Microstructural Changes in the Surface of Mortar Samples Exposed to Sulphuric Acid

Author(s): T. Schmidt, J. Neuenschwander, M. Romer, and T. Luthi

Publication: Special Publication

Volume: 234

Issue:

Appears on pages(s): 561-570

Keywords: degradation; leaky Rayleigh wave; mortar; sulfate attack; ultrasonics

Date: 3/22/2006

Abstract:
Deterioration processes on concrete structures are a result of an interaction between the concrete and its environment. In this project the mechanisms of deterioration due to chemical interaction of sulfate containing aqueous solutions are being investigated by a non destructive test method. It uses ultrasonic surface waves to investigate the topmost layer of mortar samples. A pitch and catch arrangement in immersion technique is used to generate the so-called leaky Rayleigh wave. A reduction of the measured sound velocity is proposed to be an indicator of the degradation of the surface region of the mortar sample. First measurements have been performed for reference mortar and for mortar samples exposed to aggressive conditions. A reduction of the velocity of the leaky Rayleigh wave of more than 5% could be detected. This physical alteration was compared and correlated with microscopical findings of the surface layer.