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

摘要

The suspension hydration of C3A with gypsum (inthe molar ratio of 1:3) was investigated at room temperature andwater/solid ratio of 4. The hydration was carried out in presence of1, 1, and 3% sodium salt of naphthalene-formaldehydepolycondensate and the mixes were designated as I, II, and III,respectively. The only hydration product formed in the presenceand absence of the superplasticizer was ettringite. The rate ofettringite formation was retarded by the presence of thesuperplasticizer. This effect was more pronounced at high dosageof the superplasticizer only during the first 24 h. The presence ofsodium salt of naphthalene-formaldehyde polycondensate caused adecrease in the size of the formed ettringite crystals, and as thepercentage of the admixture increased, the crystal size decreased. Inaddition, there was an interaction between the usedsuperplasticizer and the formed ettringite as indicated from infrared analysis.