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

Abstract

• The reaction models of CN/NN with C 3 A-H 2 O and C 3 A-Gp-AF-H 2 O were proposed. • It is proved that the formation of new phase is the main reason to promote the early strength of mortar. 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 C 3 A, the reaction mechanism of CN/ NN in the CN/NN-C 3 A-H 2 O and C 3 A-Gp-AF-H 2 O system was revealed by XRD and Raman: the formation of a new phase 3CaOAl 2 O 3 ·0.83Ca(NO 3 ) 2 ·0.17Ca(OH) 2 ·9.5H 2 O (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.