ABSTRACT
When increasing the temperature of the concrete, there are various chemical processes that cause mechanical and chemical changes of material. These changes have a significant impact on the physical and mechanical properties of concrete structures (modulus of elasticity, toughness, surface hardness), which are essential to meet the basic building requirements, especially mechanical strength, stability and fire safety. The paper presents the results from non-destructive testing of concrete specimens degraded by high temperatures. The test specimens were heated to 600°C. This temperature was then maintained for one, two and five hours. After heating, the samples were slowly cooled down to room temperature and then tested by acoustic non-destructive methods (Impact-echo method and one of the nonlinear acoustic spectroscopy methods). The objective was to verify whether the parameters obtained by these methods are able to describe material degradation due to high temperature and residence time at this temperature.
