The influence of calcium nitrate/sodium nitrate on the hydration process of cement paste mixed with alkali free liquid accelerator

In this paper, the effects of calcium nitrate (CN) and sodium nitrate (NN) on the setting time and mortar strength of cement paste mixed with an alkali-free liquid accelerator (AF) were investigated. The results showed that the dosage of 1.5% CN/NN can shorten and improve the early strength of cement paste and mortar mixed with AF. Combined with the reaction of CN/NN with C3A, the reaction mechanism of CN/ NN in the CN/NN-C3A-H2O and C3A-Gp-AF-H2O system was revealed by XRD and Raman: the formation of a new phase 3CaOAl2O3·0.83Ca(NO3)2·0.17Ca(OH)2·9.5H2O (nitrate-AFt) was the main reason for the improvement of the strength. At the same time, the reaction model of CN and NN in pastes was proposed. Thus, it provided a reference for investigation the influence of inorganic salt-AF on cement hydration.