light duty fire bricks as an insulation

[Chris inPA]

My cousin dismantled an old pottery kiln. He offered me the fire bricks. They are very light in weight and falling apart almost into a powder. So, there's no chance of using them for my dome build.

I'm wondering if these could be used as an insulation. Crush them with a sand tamper and use in place of perlite (in a Portland Cement mixture) on the hearth under my floor bricks. Or, should I just help him throw these away??