Study on the Destruction of Heat-Resistant Chamotte Concrete During Sharp Heating and Cooling
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Vol. 61, No. 3, September, 2020
STUDY ON THE DESTRUCTION OF HEAT-RESISTANT CHAMOTTE CONCRETE DURING SHARP HEATING AND COOLING V. Antonovich,1,3 P. Zdanevicius,1 R. Stonis,1 E. Spudulis,1 A. Koryakins,2 G. Shakhmenko,2 A. Tatarinov2 Translated from Novye Ogneupory, No. 6, pp. 41 – 46, June, 2020.
Original article submitted October 12, 2019. This study investigates the destruction of heat-resistant chamotte concrete of various classes: low-cement and medium-cement after exposure to thermal shocks. The influences of the addition of quartz sand (to increase alkaline resistance) and the addition of metal fiber (to reduce cracking) were also studied. Two methods were used to determine the heat resistance of concrete, according to the material destruction: a water-cooled plate method based on ultrasound and a method of unilateral heating-cooling. The results obtained via the method of unilateral heating-cooling revealed the formation of macrocracks in samples of low-cement concrete. This method was found to be more sensitive for evaluating concrete destruction. Keywords: heat-resistant concrete, thermal resistance, ultrasound studies.
Depending on the rate at which heating-cooling occurs, as well as its frequency, thermal stress leads to crack formation in the material and ultimately to the delamination of relatively thick surface layers of the lining. To illustrate this phenomenon, Fig. 1 shows the cases of material destruction during the rapid heating of the furnace-preheater of an oil refinery plant and during the sudden cooling of a rotary kiln at a chemical plant. Despite the advances in the study and modeling of the refractory material destruction process induced by critical thermal stresses, predicting the service life of the lining of thermal units is still difficult. Therefore, when choosing a material, its thermal resistance has to be tested according to existing methods while considering the specific operating conditions of the thermal unit. The term thermal resistance refers to the ability of a material or product to resist thermal stresses arising from a temperature gradient. To determine the thermal resistance of a refractory material, different methods are used; these methods differ in several aspects, including the heating temperature of the samples, the cooling method, and the result evaluation method [2]; therefore, the results obtained by different methods do not always agree [3]. Moreover, the test conditions in most methods (e.g., cooling in water, volumetric heating) do not correspond to the operating conditions of the material in a thermal unit.
INTRODUCTION Sharp temperature changes lead to thermal stresses in the refractory material and consequently to the formation of micro- and macrocracks and a decrease in the material mechanical characteristics. Rapid changes in temperature (thermal shock) create a large temperature gradient in the lining of the thermal unit, which results in high thermal stress in the refractory material. Thermal stress is associated with the temperature gradient and mate
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