The construction performance of refractory castable depends on its thixotropy and fluidity. To improve mobility, an effective measure is to increase water consumption. When the refractory castable composition and process conditions are the same, its performance is directly related to the water consumption. The water consumption increases, the water escapes after heating, the pores increase, the structure is loose, and various performances are reduced. Therefore, in practical applications, measures such as dispersant (or water reducer) and superfine powder are often used to control and adjust the water consumption to ensure performance.
There are three mechanisms of dispersant action:
That is, electrostatic stabilization mechanism (Electrosticstabilization), steric hindrance stabilization mechanism (Stericstabilization) and electrostatic steric stabilization mechanism (Electrostericstabilization). The electrostatic stabilization mechanism is also called the electric double layer stabilization mechanism, that is, by adjusting the pH value or adding an electrolyte, a certain amount of surface charge is generated on the surface of the particles, which increases the thickness of the electric double layer and the zeta potential value of the particle surface, so that the particles generate Larger repulsive force, and then realize the stable dispersion of particles; the steric hindrance stabilization mechanism is to add a certain amount of uncharged high molecular weight compounds to the suspension to make it adsorb on the surface of the particles to form a thicker steric hindrance layer, Make space repulsion between particles, so as to achieve the purpose of dispersion; electrostatic space stabilization mechanism is to add a certain amount of polymer polyelectrolyte to the suspension to make it adsorb on the particle surface, at this time, the polyelectrolyte can be repelled by its own charge The surrounding particles can also prevent the surrounding particles from approaching through their steric hindrance effect. The combined effect of the two can achieve the effect of composite and stable dispersion.
The dispersant is added to the castable, which can reduce the amount of water and cement, increase the fluidity, and improve the density and strength of the product. But it is not that the more the dispersant is added, the better the water reducing effect. This is because adding too much dispersant will adversely affect the performance of the product, and at the same time, too much dispersant has no positive effect on fluidity.
The form in which the dispersant is added to the castable has a certain impact on the dispersion effect. Some powder dispersants can be added directly, while some powder dispersants need to be made into a solution with a certain concentration before adding, which has a better dispersion effect.
There are several blending methods for dispersants:
(1) First mixing method: the powdery dispersant is first mixed with cement, and then mixed with water.
(2) Same blending method: the dispersant is first dissolved into a solution of a certain concentration, and then blended with water while stirring.
(3) Stagnant water method: During the stirring process, the dispersant is added after 1-3 minutes behind the water.
When the high-efficiency dispersant is mixed first, the plasticizing effect is poor. When there are coarse particles in the dispersant, it is not easy to disperse evenly, which affects the dispersion effect of the dispersant, and the flow value does not increase much. Using the same blending method, the dispersant is easy to stir evenly and has a good dispersion effect. Generally, when the same type of dispersant is added in the same amount, stagnant water method has the best dispersion effect and the largest flow value, followed by the same blending method, and the first blending method has the worst effect.