TEMPERATURE EFFECT ON THE THERMAL-PHYSICAL PROPERTIES OF FIRE-PROTECTIVE MINERAL WOOL CLADDING OF STEEL STRUCTURES UNDER THE CONDITIONS OF FIRE RESISTANCE TESTS

The value of the thermal conductivity coefficient depending on the temperature of the samples of steel rod fragments with fire-retardant cladding has been determined in the present research. The thermal conductivity coefficient of mineral wool fire-retardant cladding was determined; special patterns of its dependence on temperature were revealed. This is explained by the thermal decomposition with the release of thermal energy of inclusions between the fibers of mineral wool and its fibers at a temperature of 750 °C. The apparent minimum of the thermal conductivity factor for fire-retardant mineral wool cladding with a thickness of more than 50 mm is observed at a temperature of about 100 °C. This happens due to the fact that at this temperature the free moisture contained between the fibers of the mineral wool evaporates. Generalized temperature dependence of the thermal conductivity coefficient of mineral wool fire-retardant cladding has also been derived, in a tabular form. It can be used for calculating the temperature in steel structures with such fire protection. The thickness range for application is up to 80 mm for the specific heat capacity of 1,000 J/(kg °C) and a density of 200 kg/m3. It is shown how the obtained dependence can be used for predicting heating in steel structures with fire-retardant mineral wool cladding. The relative error between the calculated and experimental data was calculated. The Cochrane, Student, and Fischer criteria for the results of temperature calculation in steel structures with fire-retardant mineral wool cladding between the calculated and experimental data accept values that do not exceed the tabular quantities. This means that the results of the calculation using the obtained temperature dependence of the thermal conductivity coefficient are adequat