What is the calculation method of the plasticity index of batu bata tahan api?

The method for calculating the plasticity index of refractory bricks is to process the mud mass into a sphere with a diameter of 45mm, place it in a plasticizer, and compress it with gravity until cracks begin to appear. The plasticity index of refractory brick is the degree of deformation of the mud ball under the action of external force, that is, the product of stress and strain. The calculation formula is as follows:

Plasticity index S=(d－b)G

d——The original diameter of the mud ball, cm;

b——The height of the mud ball after being compressed by gravity, cm;

G——The load when the mud ball is compressed and the first crack appears, kg.