On Wed, 03 Jun 2015 13:22:42 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

Will plain old
post mix work? Do we need special cement in the concrete mix?

It's probably unlikely, but if the builders knew of this then, sodium
silicate (water-glass) solution added to the concrete will increase its
ability to manage direct heat.

It also changes the curing characteristics, so experiment or research it
before doing.

Lloyd
Been known for at least a hundred years. What you realy want is some
kind of refractory cement. Fire-Rok is one brand out there.

You want concrete that has no moisture in it - or concrete that can
let the moisture out without splitting the concrete. Using fine
plastic fibers in the agregate allows the plastic to melt and extrude,
relieving the stem pressure.