The bulk density (BD) is the amount of refractory material within a volume (kg/m3). An increase in bulk density of a given refractory increases its volume stability, heat capacity and resistance to slag penetration. The apparent porosity or open porosity (oPo) is the volume of the open pores, into which a liquid can penetrate, as a percentage of the total volume of the refractory. This property is important when the refractory is in contact with molten charge and slag. A low apparent porosity prevents molten material from penetrating into the refractory and therefore enhance it resistance to corrosion.
Several methods can be employed to measure the BD and oPo of materials, the EN 993-1 is a so-called imbibition method. The BD and oPo are there determined by weighing the mass of dry test piece, then its apparent mass when immersed in a liquid which it has been impregnated under vacuum, and then its mass in air while still soaked with liquid.
The EN 993-1 was issued in 1995 and is based on the PRE/R9 and PRE/R10 (PRE Recommendation) elaborate in 1966. The EN 1402-6 was first issued in 1998 and revised in 2003 and is based on the PRE/R28 elaborated in 1977.