Making asbestos-cement products safe using heat treatment

The paper concerns the safe disposal of asbestos containing products (eternit) by means of heat treatment. Asbestos-cement samples were heat treated at 700 °C, 1000 °C and 1300 °C for 1 h. The microstructural and phase changes induced by heat treatment were analyzed. It was found that changes in the material microstructure and asbestos fiber morphology depend strongly on the applied temperature. Total absence of the fibrous morphology phase was found only in the samples subjected to heat treatment at 1300 °C, while for the samples subjected to heat treatment at lower temperatures the share of fibrous phase was significantly reduced. The phase composition tests showed that the dominant phase in the thermally treated composite is Ca2SiO4, whose share increased with increasing the processing temperature. In the case of CaCO3, which was the dominant component of the composite matrix in the initial state, its content gradually decreased as the process temperature increased. The share of forsterite (Mg2SiO4) and enstatite (MgSiO3) formed from the decomposition of chrysotile (Mg3Si2O5(OH)4) grew with increasing the temperature. An analogous regularity was observed in the case of CaO formed from the decomposition of calcite. The diffraction reflections from the only form of asbestos present in the eternit, i.e. chrysotile, were no longer registered in the case of the sample treated at 700 °C. As a result of heat treatment eternit gradually loses its composite features due to the thermal decomposition of chrysotile. The consequence of this process was a significant reduction in the strength properties of the material. Keywords: Asbestos-cement building composite, Chrysotile, Thermal treatment, Microstructure, Phase evolution