Technical calcium nitrate as set accelerator for cement at low temperatures

Abstract The objective was to test the efficiency of technical calcium nitrate (CN) as a set accelerator for different cements at low temperatures (5–7 °C). The applied dosages were 0.00, 1.55, 2.32, 3.10, 3.86 and 7.73 % CN of the cement weight, corresponding to 0.00, 1.00, 1.50, 2.00, 2.50 and 5.00 % NO 3 , respectively. Five different portland cements were chosen covering a wide range in C 3 A contents, since it was initially believed that the set regulating mechanism involved C 3 A (i.e. the efficiency depend on the C 3 A content). The setting characteristics of the cement pastes with w c = 0.40 were determined by an automatic Vicat-needle apparatus in a room with an ambient temperature of 5–7 dgC. The results revealed that the set accelerating efficiency of CN depended very much on the cement type. However, no correlation with the C 3 A content was found. On the other hand, the set accelerator efficiency of CN seems to increase with increasing belite content according to the Bogue analyses of the cements, or other cement characteristica promoting belite formation in the clinker process.