In order to achieve higher mechanical strength in the early stages, ordinary refractory castables often have a higher proportion of cement content (10%~15%, weight ratio), but this also leads to a series of performance declines in refractory castables, due to:
1. In order to achieve complete hydration of cement, excessive external water (10%~15%) during mixing causes high porosity and density reduction in ceramic refractory castables.
2. Calcium aluminate hydrate exhibits strong dehydration and recrystallization effects during the medium temperature stage, disrupting the microstructure of hard points in the castable and causing a sharp decrease in the strength of refractory castables during the medium temperature stage.
3. Cementitious binders introduce a large amount of impurities into the castable, resulting in a decrease in the load softening temperature and deterioration of the thermal shock stability performance indicators of the vitrified refractory castable. In response to the poor high-temperature performance of ordinary refractory castables, low cement refractory castables effectively avoid the regret of high temperature performance. The so-called low cement refractory castables have a cement content of less than 8%, while those with a cement content of less than 4% are called ultra-low cement refractory castables. In contrast, the aforementioned shortcomings of ordinary refractory castables have been transformed into the advantages of low cement refractory castables. Its structure is dense. Low apparent porosity, high fire resistance, high load softening temperature, high high-temperature strength, and good thermal shock stability. However, due to its low cement content, it has a long setting time and low early strength, which is particularly unfavorable for construction in winter and low temperature conditions. Therefore, sufficient attention should be paid during masonry construction
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