Effects of superplasticizers on the stability and morphology of ettringite

Stability and morphology of ettringite with and without four different superplasticizers, namely, polycarboxylic acid, naphthalene sulfonate, amino sulfonate, and aliphatic superplasticizers, were investigated on hydration and synthetic samples. Thermogravimetric analysis, X-ray diffraction, scanning electron microcopy, and X-ray photoelectron spectroscopy were used for analysis. The stability of ettringite increased when naphthalene sulfonate superplasticizer was used, whereas the stability decreased when the three other superplasticizers were applied. The stability further increased because of the morphology of the formed ettringite crystals. In addition, certain chemical reactions occurred between ettringite and the superplasticizers, particularly the polycarboxylic acid. Some calcium complex chelate compounds were also produced, and the hydration products obtained with polycarboxylic acid and naphthalene sulfonate were more compact and stable than those obtained with the two other superplasticizers.