what are refractory castables?

Answer 1

I'd never heard the term before, but since nobody else answered I did a search and found this...
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REFRACTORY CASTABLES:

Dry materials that can be combined with water to form a homogenous mass which can be cast in formwork similar to concrete.

Castable refractories can be classified into four major groups - dense castables, lightweight or insulative castables, gunning castables, and special purpose castables - sometimes these classifications can be combined, such as lighhtweight gunning castables, or dense gunning castables.

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Hope that helps.

Answer 2

These are materials which consist of precision graded coarse and fine refractory grains. They are gelled by means of a binder system in the materials green state. Following the heat-up of the material the binder either transforms or volatilises facilitating the formation of a ceramic bond. The most common binder used in castables is HAC (high alumina cement). Other binders that are often used include hydratable aluminas and colloidal silica. Castables are mixed with water and then installed by either pouring or pumping. Placement of the material then requires vibration.

Answer 3

Refractory materials are those which resist heat. So a refractory castable is a material that can be cast (like cast concrete or plaster) AND is heat resistant. Concrete and plaster do not resist serious heat very well.