INFLUENCE OF CALCIUM NITRITE ON THE EARLY-HYDRATION OF ALUMINATE AND FERRITE PHASE IN ORDINARY PORTLAND CEMENT

Abstract

This paper discusses the influence of calcium nitrite on the early hydration reaction of the Ordinary Portland Cement（OPC）. The AFm phase containing nitrite ion（AFm（NO₂）, Ca₃Al₂O₆・Ca（NO₂）₂・10H₂O）and ettringite（Ca₃Al₂O₆・3CaSO₄・32H₂O）are formed after 1-day hydration time. Even after 30-minute hydration time, these hydrated products are formed. Also, these are remained in the 14-day samples without changing the other hydrations. By adding calcium nitrite, the amount of cumulative heat evolution of OPC increases after 48 hours. In this 48 hours, the reaction rates of aluminate phase（Ca₃Al₂O₆）and ferrite phase（Ca₄Al₂Fe₂O₁₀）in the OPC mixed with calcium nitrite are more than 1.5 times larger than those without calcium nitrite. When calcium nitrite is added to aluminum phase and gypsum and hydrated for 30 minutes, hydrated products are observed around the unreacted grains by SEM photograph. We considered that the accelerations of the aluminate phase and the ferrite phase in the OPC are related to the formation of those hydrations. Adding calcium nitrite to the OPC accelerates the reactions of the aluminate phase and that of ferrite phase in the OPC during the early stages of hydration.