The mechanical strength (σcr) and pyroplasticity index (IP)
were determined from prism-shaped test pieces, 6 mm thick,
20 mm wide, and 80 mm long. The bending strength was determined
by the three-point bending method (Instron, Universal
testing machine 6027) and the pyroplasticity index by measuring
the test piece deflection (s), when the samples were fired
while supported by their centre area, according to the following
equation16: