Effect of sodium salt of naphthalene-formaldehyde polycondensate on ettringite formation

The suspension hydration of C(3)A with gypsum (in the molar ratio of 1:3) w as investigated at room temperature and water/solid ratio of 4. The hydrati on was carried out in presence of 0, 1, and 3% sodium salt of naphthalene-f ormaldehyde polycondensate and the mixes were designated as I, II, and III, respectively. The only hydration product formed in the presence and absenc e of the superplasticizer was ettringite. The rate of ettringite formation was retarded by the presence of the superplasticizer. This effect was more pronounced at high dosage of the superplasticizer only during the first 24 h. The presence of sodium salt of naphthalene-formaldehyde polycondensate c aused a decrease in the size of the formed ettringite crystals, and as the percentage of the admixture increased, the crystal size decreased. In addit ion, there was an interaction between the used superplasticizer and the for med ettringite as indicated from infrared analysis. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.