Generally, in the formulation of refractory castables, the proportion of aggregate and refractory cement accounts for about 80%, while the proportion of additives is less than 20%. Although the proportion of additives is only less than 20%, there are many types of additives including water reducing agents, plasticizers, gelling agents, degelling agents and other additives, and they play a vital role in refractory castables. effect. It improves the construction performance, physical performance and use performance of refractory castables. The method of using additives is to add them during or before the stirring of the refractory castable. The amount of additives added is proportional to the properties and functions of the refractory castables, and is a few ten thousandths to a few percent of the total.
Classified according to the chemical composition and properties of additives:
(1) Inorganic substances-various inorganic electrolytes, some simple metals, a small amount of inorganic minerals, oxides and hydroxides, etc.
(2) Organic substances-most of them belong to surfactants, which have hydrophilic and hydrophobic groups. Hydrophilic groups that can ionize in water are called ionic surfactants, and those that do not ionize are called non-ionic surfactants. The ionic surfactants can be divided into anionic, cationic and amphoteric surfactants. In addition, there are some polymer surfactants, organic acids and so on.
Classified according to the function of additives:
(1) Additives that change rheological properties (workability), including water reducing agents (dispersants), plasticizers (plasticizers), gelling agents (flocculants), and debonding agents (deflocculants).
(2) Additives that regulate the speed of coagulation and hardening, including accelerators, retarders, delayed hardening accelerators, etc.
(3) Additives for adjusting the internal structure, including foaming agents (air-entraining agents), defoamers, shrink-proofing agents (expanding agents), etc.
(4) Additives to maintain the construction performance of materials, including acid inhibitors, preservatives, etc.
The nature and function of water reducing agent
Under the condition that the flow value of refractory castable is kept basically unchanged, the substance that can significantly reduce the amount of concomitant water is called water reducing agent (precipitation agent). The water reducing agent itself does not chemically react with the material composition to generate new compounds, but only plays the role of surface physics and chemistry. Therefore, they are a surface active substance or an electrolyte. After they are dissolved in water, they can be adsorbed on the surface of the particles, increase the potential of the particle surface, increase the repulsive force between the particles, and release the free water wrapped in the condensed structure composed of fine particles, thereby playing a wetting and dispersing effect. Also known as dispersant. Because it can release free water in the cohesive structure, it can reduce the unit water consumption while maintaining the rheology (workability) of the castable, or improve the workability without changing the unit water consumption. The material is easy to construct and shape.
