Refractory Technology
Spalling of a refractory means its

Softening
Resistance to chemical action of gases and molten fluxes
Fracture due to uneven expansion at high temperature
Resistancce to compressive loads

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Refractory Technology
Addition of grog in fireclay brick during its manufacture is advantageous, because it results in

All of these
Less addition of water to get a workable plasticity & lesser time required for drying the raw refractories and hence increased rate of production
Less shrinkage in heating, decreased apparent porosity & increased specific gravity
High strength & thermal spalling resistance

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