Stability of Ettringite in the Presence of Superplasticizers

摘要

The stability of synthesized ettringite in the presence of naphthalene and carboxylated superplasticizers was explored in this study. In the absence of superplasticizers, ettringite was found stable in aqueous solutions with pH around 10. However, in the presence of superplasticizers during the synthesis, resulting ettringite was stable at pH other than 10. The weight loss of ettringite was reduced in solutions with pH 4, pH 9, and pH 11. The carboxylated superplasticizer had a greater stabilizing effect than naphthalene-based superplasticizer in both acid and basic solutions. Moreover, in the presence of superplasticizers, X-ray diffraction (XRD) patterns showed that the amounts of ettringite were increased and the secondary electron microscopy (SEM) showed that the morphologies of the ettringite crystals were larger, again suggesting the stabilization of ettringite. Results in this study may explain the cement-admixture compatibility problems due to the ettringite formation during the early hydration of cement pastes.