Effect of Water Reducing Agent on Fluidity of Refractory Castables

Water reducer can reduce the water consumption of refractory castables and improve the fluidity of refractory castables, making them easy to construct and dense. For example, the effects of sodium hexametaphosphate (SHP) and ammonium polyacrylate on the rheological properties of high-aluminum, low-cement self-flowing castables were studied. Self-flowing castables can be obtained by adding 0.05% SHP and 4.5% water. Higher fluidity can be obtained by adding 0.1% ammonium polyacrylate and 5% water. However, the former has a certain retarding effect on the castable, while the latter has better adhesion and is not easy to bleed water.

The effects of sodium hexametaphosphate (SHP) and sodium polyacrylate as water reducers on the rheological properties of Al2O3-SiC-C castables were studied. SHP anionic water reducer ionizes when in contact with water and adsorbs on the surface of particles to reduce its ζ-potential value, thereby improving the fluidity of the castable. Sodium polyacrylate is a polymer polyelectrolyte. After dissociation in water, it improves the rheological properties of the castable through electrostatic repulsion and steric hindrance. However, the dissociation of sodium polyacrylate will lead to a strong increase in the viscosity of the solution, which will have a negative impact on the rheological properties of the castable. When sodium hexametaphosphate (SHP) and sodium polyacrylate are added at 0.03% and 0.05%, respectively, the flow value of the castable can reach the maximum value. Sodium hexametaphosphate shows better dispersion effect.

The effects of sodium tripolyphosphate (STP), sodium hexametaphosphate (SHP), a composite of STP and SHP in a ratio of 3:2, and calcium lignin sulfonate on the rheological properties of corundum self-flowing castables were compared. Since the water reducer forms charged colloids by electrolysis in water, it changes its ζ-potential after being adsorbed by the matrix particles, achieving the purpose of dispersing the matrix particles, reducing water, and improving the rheological properties of the slurry. The results show that there is a certain water-reducing effect under the condition of appropriate addition amount. However, the water-reducing effect of sodium hexametaphosphate (SHP) added at a dosage of 0.04% is the best.

The effects of sodium tripolyphosphate (STP), sodium hexametaphosphate (SHP), sulfonated tar (FE), and aminosulfonate (PA) water reducers on the performance of high-alumina cement castables were compared. Good water-reducing effects can be obtained under the conditions of their respective addition amounts. FE has a higher water-reducing rate and PA has the worst. FE and excessive STP show a significant inhibitory effect on the strength development of the castable.

The effects of three types of water reducers, wood sulfonate, sulfonated melamine formaldehyde, and naphthalene sulfonate formaldehyde condensate, on the performance of CA-50 aluminate cement castables were studied. The water-reducing rates of the three water reducers can reach 10-15%, but wood sulfonate has a significant retarding effect and air entraining effect. The water reduction rate of sulfonated melamine formaldehyde is the best and it also has a coagulation accelerating effect. The three have different degrees of reduction in the early strength of the castable.

The effect of water reducer on the rheological behavior of corundum castable matrix was studied. The effects of three water reducers, sodium tripolyphosphate, polyethylene glycol and dispersed alumina, on the rheological properties of two corundum castable slurries were studied. In the mixed slurry of corundum fine powder, calcium aluminate cement and silica powder, sodium tripolyphosphate and polyethylene glycol had better dispersing effect. In the mixed slurry of corundum fine powder, α-Al2O3 powder and AI2O3/SiO2 gel powder, dispersed alumina had better dispersing effect. In the study of the rheological properties of high-purity self-flowing castable, the effect of sodium hexametaphosphate (SHP), citric acid and sodium polyacrylate (Darvan811D) composite system and polymelamine sulfonate sodium salt (Meladyne) as water reducers were compared. The water addition amounts were 4.5% and 4.7% respectively, and it was found that the fluidity and working performance of the self-flowing castable were significantly improved. Sodium polyamine sulfonate is an admixture widely used in cement concrete to obtain good flowability, workability and mechanical properties. It has recently been applied by refractory technicians in aluminate cement systems.

The effect of admixtures on the usable time of high-alumina cement was studied, and sodium polyacrylate, sodium polymethacrylate, sodium polymonoester, β-naphthalenesulfonic acid and polyethylene glycol were compared. These organic water reducers mainly achieve the effect of improving fluidity and delaying setting time through electrostatic repulsion and steric hindrance. Among them, sodium polyacrylate has the best effect in extending the usable time, which can reach 160 minutes. However, due to its strong air carrying capacity, the porosity of the castable is very high after hardening, and the strength shows a downward trend. By adding a defoamer, the strength can be improved, but the usable time is shortened. Its mechanism is still under study.