Hydration reactions of the system C₃A-CaSO₄.2H₂O (1 : 1 mole ratio) at 30 and 50°C. Part II: Effect of naphthalene formaldehyde sulfonate

Essam A ¹; Wafaa S. Hegazy ¹; Doaa Abd El monem Ahmed ²

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Source: Advances in Cement Research, Volume 23, Issue 3, May 2011 pages 123 –128

Abstract

Hydration characteristics of tricalcium aluminate and gypsum mixture with a mole ratio of 1 : 1 in the presence and absence of sodium salt of naphthalene formaldehyde sulfonic acid polycondensate (NFS) at 30 and 50°C were investigated. Different ratios of NFS were used, namely 0, 1, and 3% by weight. The water-to-solid ratio used was 10. Hydration was carried out for various time intervals from 0·5 h and up to 90 days. The results of combined water content, X-ray diffraction and scanning electron microscopy indicate that NFS retards the formation of ettringite and accelerates its transformation to monosulfate at early hydration ages. The extent of transformation is inversely proportional to the ratio of NFS.