Master thesis introduces evaluation of the mechanical properties of limestone concrete after exposure to various high temperatures, i.e. 200 °C, 400 °C, 600 °C or 800 °C, using nondestructive and destructive tests. Experimental study was carried out on two concrete mixtures M1 and M2. The only difference between them was in water to cement (w/c) ratio. With each mixture we prepared 15 cubic samples dimension 10 × 10 × 10 cm3 and 15 prismatic samples dimension 4 × 4 × 16 cm3, for each temperature level three cubic and three prismatic samples. The basic mechanical properties of concrete samples were investigated in the research, i.e. compressive strength, flexural strength, surface strength, dynamic elastic, and shear modulus. Initial or reference values at room temperature 20 °C were measured on concrete samples after standard curing time proposed by standard SIST EN 12390-2:2009. Each group of samples was then placed in an electric furnace and exposed to a certain high temperature level. The development of the temperature inside the samples was monitored via built-in thermocouples. After exposure to a certain high temperature level, the samples were slowly cooled down to a room temperature. Afterwards, the specimens were initialy visually inspected to assess the damage of the concrete surface. Further on, various nondestructive tests including ultrasonic (US) method, determination of rebound number, and resonant frequency method were performed. Finally, to determine the residual mechanical properties of specimens after exposure to high temperature destructive tests were carried out, i.e. the compressive and bending test.
It was found out that high temperatures have the greatest impact on the reduction of dynamic elastic properties (Edyn and G), followed by flexural strength (fcf) and compressive strength (fc). While the impact of high temepratures on surface strength (fc,surf) is the lowest. Additionaly, analysis of variance (ANOVA) showed that the influence of temperature on experimental results is highly statistically significant for both mixtures M1 and M2.
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