Use of castables is increasing significantly in ferrous, non-ferrous and other industries due to several advantages over shaped items. Different properties of refractories are key measure to assess its performance. The most important properties are HMOR (Hot modulus of rupture), RUL (Refractoriness under load), creep, thermal shock resistance etc along with other physical properties. Several works have been conducted both in ultra low cement and low cement systems to improve all these properties by designing products with different raw materials. But in most of the cases shaped items show superior thermo-mechanical properties over low or ultra low cement castables. Use of calcium aluminate binder is common for designing castables to get initial strength. Control addition of casting water can enhance the initial strength and other physical properties. Several super fine materials have been tried to reduce casting water like reactive/calcined alumina, spinel, micro-silica etc. Addition of micro-silica has certain advantages as it gives cost effective products and help to form secondary mullite by reacting with reactive/calcined alumina present in matrix. But the amount of calcium aluminate binder and micro-silica has remarkable effect on different thermo-mechanical properties of low cement castables. In present work, 70% Al_2O_3 low cement castable has been designed with different calcium aluminate binder and micro-silica. Total amount for both is kept at 10% varying micro-silica from 2% to 8%. All relevant properties are measured for each batch along with other thermo-mechanical properties particularly HMOR. Probable explanations are given for different thermo-mechanical properties due to different amount of calcium aluminate binder and micro- silica in the system on the basis of phases formed during firing and micro structure analysis.
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