(Received 6 November 1998; accepted 2 December 1999)
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Using the mini-slump and slump tests, three low-alkali Portland cements were found to be incompatible with a PNS superplasticizer in terms of fluidity loss in cement pastes and con-cretes having low W/C ratios (0.30 to 0.35). The addition of a small amount of sodium sulfate appeared to be a practical method to solve the slump loss problem of these superplasticized cement pastes and concretes.
The addition of sodium sulfate between 0.2 to 0.8% (or at a Na2O eq. of 0.10 to 0.35%) significantly reduces the rate of the slump loss and maintains a high slump value over 90 min after mixing of the superplasticized concrete mixes having a W/C ratio of 0.30. Moreover, the addition of sodium sulfate was not found to affect the air content of the fresh concretes. The setting of the concretes are retarded or accelerated by no more than 2 h depending on the amount of sodium sulfate added. Furthermore, the addition of sodium sulfate up to 0.5% to the superplasticized concretes increases not only the 1-day compressive strength but also the 28-day compressive strength. The addition of sodium sulfate over 0.5% was found to increase the 1-day compressive strength but to decrease the 28-day compressive strength.
Ph.D. candidate, University of Sherbrooke, Sherbrooke, QC
Professor, University of Sherbrooke, Sherbrooke, QC
Research engineer, Technical Direction, Ditec Development, Obourg,
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