Phase changes during the early hydration of Portland cement with Ca-lignosulfonates

The influence of two Ca-lignosulfonates (LS), one softwood (LSs) and one hardwood (LSh) based, on the phase changes during the early hydration of ordinary Portland cements was investigated using isothermal calorimetry, in-situ XRD, and thermal analysis. In the presence of LS the hydration of C3S and C3A was retarded. LS was found to influence the solubility of the sulphate phase; in case of bassanite/gypsum the initial dissolution was accelerated. An acceleration of the initial ettringite formation was observed in the presence of LS. However, the second ettringite formation was retarded. The amounts of bound water (H) and calcium hydroxide (CH) formed were measured using TG/DTG on cement pastes hydrated for 90 min, 5, 12 and 24 h. At 90 min the amount of H was increased the higher the concentration of LS. The amount of CH formed between 5–24 h was decreased the higher the concentration of LS.