The requirements for refractory performance in industrial environments have been increasing, and high-density deflocculated castables have been developed and improved over the past few decades. Technological advances have led to better overall performance, but the workability of the material is still susceptible to compromise. Workability is key to ensuring the optimal performance of the material.
Low cement refractory castables consist of coarse aggregate, fine fillers, one (or more) binders, and a variety of additives, specifically active compounds.
(1) Name a range of blending and additive products used in the refractory industry;
(2) Design functional additives and study their performance in combination with calcium aluminate cement;
(3) Explain the problems faced by the refractory industry when using amorphous materials by converting common knowledge into product form. Castable formulation, chemistry, and particle size are important for refractory materials, but the additive system is also critical because it affects workability, hardening kinetics, and drying properties. Designed active compounds can provide more functionality, including rheology modification, hardening mechanics, and easier drying properties. Calculated by weight (0.1%~2.5%), they only account for the smallest part, but have the greatest impact on construction performance.
1. Deflocculating agent for silica fume castables
The first active compound is REFPAC100, developed in 2015, with the purpose of improving the construction performance of low cement refractory castables containing silica fume. The designed dosage is 1%. The main advantages of the compound are related to high-temperature qualitative properties, such as silica fume quality, raw material quality (impurities in fine powder), and ambient temperature changes.
2. Deflocculating agent for high-aluminum low-cement castables
REFPAC500 is a deflocculating agent used for high-aluminum systems and castables containing alumina, magnesium oxide or magnesium spinel. In addition to low water demand, it also has high fluidity. The setting time of the product is little affected by the ambient temperature because it starts the hardening mechanism at low temperatures and has little effect on high and low temperatures.
3. Enhanced deflocculation permeability to facilitate drying
REFPAC Mipore 20 is a powder that is easily added to the dry mix, which changes the usual hydration process of calcium aluminate cement, resulting in a gel-like microstructure that provides higher permeability. The low cement refractory castables were visibly changed after drying at 110°C, which is lower than the temperature of traditional fibers (about 150°C).
Low-cement castables require suitable additives to achieve superior construction and performance properties. Some additives have been developed according to this method, such as REFPAC F461 (summer version of REFPAC 100), which extends the use time by 1h at 40°C; the accelerated version of REFPAC 500 (PP305), which has a shorter demoulding time; and the improved version of REFPAC 100 (PP306) with better deflocculation effect.
