Which property indicates the durability of a refractory material when subjected to both heat and mechanical stress?

Explanation

Refractoriness Under Load (RUL) measures the ability of a refractory to withstand deformation under high temperature and load, reflecting its mechanical strength in service conditions. Porosity refers to the volume of pores, specific gravity relates to material density, and thermal conductivity describes heat flow, none of which directly measure strength under combined heat and load.