Post-fire assessment of mechanical properties of concrete with the use of the impact-echo method

• The impact-echo device was used to test concrete damage due to high temperature exposure.
• The resonance frequency of obtained signal decreases with higher thermal damage.
• The propagation velocity slows with higher level of thermal damage of concrete.
• The formulas for concrete mechanical properties evaluation by impact-echo method were established.

The paper presents the nature of elastic wave transition obtained in the time domain and the wave propagation velocity for the impact-echo method employed on the surface of concrete cubes 0.15 × 0.15 × 0.15 m3 subjected to heating in the temperature range of 200–1000 °C. The relations between the characteristics of the obtained impact-echo signal and the mechanical properties of concrete subjected to high temperature were presented as regression curves. The paper proposes certain formulas to be employed while assessing fire-damaged concrete element. The results obtained on fire damaged concrete slab 1.2 × 1.0 × 0.3 m3 indicate a strong relation between the impact-echo parameters and the mechanical properties of concrete.