Effect of water-reducing chemical admixtures on early hydration of cement

Four water-reducing chemical admixtures: calcium lignosulfonate, amino-sulfonic-based superplasticiser, sulfonated naphthalene formaldehyde and sulfonated melamine urea formaldehyde resin were added to Portland cement paste in amounts ranging from 0 to 0.6%, at a constant water/cement ratio of 0.4 and their early hydration was investigated for up to 72 h. The results show that the rate of hydration during the hydration staring period was accelerated and the hydration induction period was extended by the four water-reducing chemical admixtures. Sulfonated naphthalene formaldehyde has the most encouraging effect on hydration and made the hydration peak rate increase to 60 kJ/kg per h in a dosage of 0.6% during the hydration starting period. By increasing the induction period and reducing the second hydration peak rate of cement paste strongly, calcium lignosulfonate was found to be the most effective retarder among the four water-reducing chemical admixtures. When the dosage of calcium lignosulfonate was 0.6%, the hydration induction period of the cement paste was extended from 10 to 40 h. The use of a 0.6% dosage of amino-sulfonic-based superplasticiser extended the induction period from 6 to 29 h. With the addition of sulfonated naphthalene formaldehyde and sulfonated melamine urea formaldehyde resin, the induction period was only slightly affected. It is interesting that the second hydration peak rate of cement paste increased with the dosage of sulfonated melamine urea formaldehyde resin, which differed from other three water-reducing chemical admixtures.