Influence of Superplasticizers on the Early Hydration of Portland Cement and Cement Compounds

摘要

The interaction of superplasticizers with portland cement, pure alite (C3A) was studied using adsorption studies, calorimetry, x-ray diffraction, thermal analysis, and scanning electron microscopy. Three different superplasticizers - Mighty 100, Melment L-10A, and Mulcoplast - were used. The superplasticizers were strongly and rapidly adsorbed by all cements and cement compounds. Adsorption was greatest into C3A, but in the presence of gypsum the rate of adsorption was slower. No correlation was observed between adsorption and initial slump or slump loss. Slump loss was greatest for mortars made with pure alite. The very early hydration reactions were retarded by the superplasticizers. In the case of C3A the composition of the hydration products were unchanged in the first hour of hydration, but morphological differences were observed. Changes in the hydration of alite and cements during the first hour could not be adequately documented using the available techniques.