The main reasons for the deformation of ventilation ducts are as follows:
1. Magnesium cement undergoes a continuous expansion process under natural curing conditions, with a linear expansion rate of 0.1-0.2% and a volume expansion rate of approximately 1%.
2. During the sintering process of magnesite, local overburning is inevitable, causing a portion of MgO to be in a dead burning state. The hydration process of overburned MgO is slow. When MgO in the cement stone that has formed strength is hydrated again with water, it generates Mg (OH) 2, with a volume expansion of 120%.
3. During the hydration of free CaO in lightly burned magnesium oxide, the volume expands by 90%, while there is SO42- present in the brine sheet. When Ca (OH) 2 is converted into gypsum, the solid volume will increase by more than twice, causing deformation of the product. This is also the reason for limiting the content of free CaO in lightly burned magnesium oxide and SO42- in the brine sheet.
4. The hydration process of MgO-Mg-C12-H2O system is a strong exothermic reaction process, and the volume of the produced pipeline is large. If the ambient temperature is high, the reaction temperature will rise, and the temperature of the board body will be too high, resulting in insufficient reaction and causing significant crystallization stress and thermal expansion stress, causing the volume of the product to expand.