Effect of Sodium Sulfate Addition on Properties of Cement Pastes Containing Different Molecular Weight PNS Superplasticizers

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Title: Effect of Sodium Sulfate Addition on Properties of Cement Pastes Containing Different Molecular Weight PNS Superplasticizers

Author(s): B.-G. Kim, S. Jiang, and P.-C. Aiitcin

Publication: Special Publication

Volume: 195

Issue:

Appears on pages(s): 485-504

Keywords: adsorption; alkali; cement; superplasticizer

Date: 7/1/2000

Abstract:
The effects of Na2S04 addition to cement pastes containing PNS superplasticizer with different molecular weight were investigated in different parameters of cement pastes, such as the rheological properties, the adsorption of PNS superplaticizer, and the development of the heat of cement hydration. Na2S04 addition significantly improves the fluidity of cement pastes made with a low-alkali-cement and a high-molecular-weight PNS. On the contrary, Na2S04 addition to a high-alkali-cement has a negative effect on the fluidity of cement pastes in the presence of PNS superplasticizer. The effect of Na2S04 addition on the fluidity of cement pastes made with a low-molecular-weight PNS is relatively small. When sodium sulfate is added to the low-alkali cements in order to adjust the soluble alkali content, it is confirmed that the cement pastes containing the high-molecular-weight PNS have better fluidity than those containing the low- molecular-weight PNS. The Na2S04 addition reduces the amount of PNS adsorbed on cement particles and the effectiveness of Na2S04 in reducing the amount of PNS adsorbed is independent to the molecular weight of the PNS. The Na2S04 addition to low-alkali-cements retards cement hydration during induction period in the presence of a high-molecular-weight PNS and then accelerates it during the acceleration period. However, the Na2S04 addition to high-alkali-cements just accelerates cement hydration and this acceleration effect is not dependent to the molecular weight of PNS super-plasticizer.