Compositions and Applications

Several ways of classifying these refractories have been listed according to physical

and chemical properties or applications [40, 41]:

• Method of installation: pouring/casting, trowelling, gunning (shotcreting), vibrating, ramming, and injecting

• Use or application: materials for monolithic constructions, materials for repairs, materials for laying and forming joints (mortars)

• Type of bond: hydraulic bond with hardening and hydraulic setting at room temperature, ceramic bond with setting by sintering during firing, chemical bond (inorganic or

organic-inorganic) with setting by chemical but not hydraulic reaction at room temperature or at temperature below the ceramic bond, and organic bond by setting or hardening at room temperature or at higher temperatures

• Chemical composition: silica-based and silica-alumina-based materials, chrome, magnesia, chrome-magnesia, spinel, SiC, materials containing carbon (more than 1% carbon or graphite), and special materials (containing other oxides or materials such as zircon, zirconia, Si3N4, etc.)

• Bulk density: lightweight (bulk density below 1.7 g cm-3) and dense castables

• Norms and Standards: for instance ISO (International Organization for Standardization), and ASTM (American Society for Testing and Materials)

Calcium aluminate cements are examples of conventional refractory castables. Develop­ment of low, ultralow cement, no-cement pumpables, and self-flow castables has increased the applications of monolithics [42]. Steel-reinforced refractories (SFRR) are used in applications that include ferrous and nonferrous metal production and processing, petroleum refining, cement rotary kilns, boilers, and incinerators. Steel fibers are added to refractory concretes to improve resistance to cracking and spalling in applications of heavy thermal cycling and thermal shock loads.

Phosphate-bonded monolithic refractories are available both as phosphate-bonded plastic refractories and phosphate-bonded castables. Phosphate-bonded plastic refrac­tories contain phosphoric acid or an Al-phosphate solution. They are generally heat setting refractories, developing high cold strength after setting, and are highly resistant to abrasion. Phosphate-bonded castables contain no cement, and magnesia may be added as setting agent [40].