Title: Setting Accelerator Calcium Nitrate Fundamentals, Performance and Applications
Author(s): Harald Justnes and Erik C. Nygaard
Publication: Symposium Paper
Appears on pages(s): 325-338
Keywords: Accelerating agents; admixtures; cement types; compressive strength;
setting (hardening); temperature.
The effectiveness of calcium hitrate (CN) as a setting accelerator for cement is dependent on the cement type. The reason for this is explained by the mechanisms for set acceleration, and parametres for predicting the set accelerating efficiency of CN from cement characteristics is pointed out. Performance characteristics such as temperature evolution profile in insulated concrete (i.e. semi-adiabatic) and early compressive strengths (from 8 h) of concretes cured at 20°C for different additiom of different soluble calcium salts are demonstrated. The accelerating effect of CN was compared to additions of both calcium acetate and fortnate on equimolar concentrations of Ca2+ Calcium acetate and formate gave about the same accelerating effect, while CN showed greater acceleration. The difference might be due to an increased content of free Ca2+ (i.e. hot complexed ion) in CN compared with the organic acid salts. The temperature profiles revealed that CN accelerates set and hot the rate of early strength development. However, the 8 h compressive strength was increased when CN was added due to parallel displacement of the temperature evolution curves towards earlier times. Examples are given for field use (e.g. regulating slip forming rates) and potential applications (e.g. element production) of CN in concrete.