Early hydration of C3A–gypsum pastes with Ca- and Na-lignosulfonate

The early age phase development during the hydration of C3A–gypsum pastes with 1 and 4% Ca- or Na-lignosulfonate (CLS and NLS) was investigated using isothermal calorimetry, in-situ XRD, thermogravimetry, mass spectroscopy, and SEM analysis. With 1% CLS or NLS neither retardation of C3A dissolution nor retardation of ettringite formation was observed. When LS was added in a concentration of 4%, C3A and gypsum dissolution were slightly retarded. Gypsum depletion was delayed in all pastes containing CLS or NLS. 1% CLS or NLS increased the amount of AFm-phases formed within 24 h, while the amount of AFm was reduced with 4% CLS or NLS. The initial heat flow increased and the heat flow in the gypsum depletion peak was reduced with 1 and 4% CLS. With 4% NLS no initial heat flow was measured and the heat developed slowly within the first 15 min of hydration in the C3A–gypsum paste.