Impact echo and low frequency ultrasonic testing for assessment of damage to concrete blocks exposed to sodium fire

Abstract

This study aims to establish nondestructive methodologies for assessment of damage to concrete after exposure to a sodium fire. Impact/echo and through-transmission low frequency ultrasonic (500 kHz) measurements have been carried out on concrete blocks and extracted core specimens before and after exposure to sodium fire. A decrease in ultrasonic velocity and an increase in ultrasonic attenuation are observed after exposure to sodium fire. The ultrasonic and the compressive strength measurements on the specimens extracted from different depths in the concrete blocks indicate that the damage is confined to within about a 70 mm depth from the concrete surface exposed to the sodium fire. It is inferred from this that the thickness of the sacrificial layer of sodium resistant concrete should be at least 70 mm. It is demonstrated that in situ impact/echo testing can be used to detect damage to the concrete, even in the cases where the concrete surface can be accessed from one side alone.