Influence of Setting Accelerators on Chemical Shrinkage of Portland Cement

Abstract

The influence of a number of calcium salts on the total chemical shrinkage (used as a measure of cement hydration) of different portland cement pastes was followed during the first 48 hours. All calcium salts (acetate, chloride, formate, nitrate and nitrite) were added in an equimolar dosage of Ca2+ corresponding to 1.5% calcium nitrate by cement weight. An automatic Vicat-apparatus was used to monitor the setting time of the cement pastes. Experiments conducted at 5 degrees C, 13 degrees C and 23 degrees C revealed that calcium nitrate was the most effective set accelerator at lower temperatures and even more effective than calcium chloride at the lowest temperature. The anions of the different calcium salts were also found to influence the setting and the efficiency of each accelerator strongly depended on the cement types.