Refractories - Low Cement, Ultra Low Cement and No Cement Castable Refractories

When it was discovered that the addition of highly reactive volatilised or fume silica to a castable would dramatically change the physical properties, a new family of castables resulted. These dense strong refractory castables, based on the use of low calcium aluminate cement content, have replaced many conventional castables, plastics, ramming and gunning mixes and are used in many applications that require high refractoriness, corrosion resistance and abrasion resistance. These castables possess a uniform structure with low porosity; have high temperature strength throughout the low and intermediate temperature range. Today virtually every refractory castable manufacturer has a complete line of these low cement castables, ultra-low cement and no cement castables.

Classifications

These three types of castables have been classified by ASTM as:

• Low Cement containing 1.0% to 2.5% CaO
• Ultra-Low Cement 0.2% to 1.0% CaO
• No Cement Castables with up to 0.2% CaO.

Physical Properties

Typical properties for these three types are shown in Table 1, Table 2 and Table 3.

Table 1. Typical physical properties of low cement castables (LCC).

Table 2. Typical physical properties of ultra low cement castables (ULCC).

Table 3. Typical physical properties of no low cement castables (NCC).

Applications

These low cement-type castables find many applications through industry including the steel, iron and steel foundries, aluminum furnaces and other non-ferrous metals, rotary kilns, incinerators and also for making precast shapes. The strength which are developed in these castables are often equal to or greater than fired products.

Note – A complete list of references can be obtained by referring to the original text.

Primary author: Edwin Ruh

Source: Abstracted from International Ceramic Monographs, Vol. 1, no. 2, pp. 772-93, 1994.