Research on the influencing factors of free nitrite ions content in cement paste

This paper aims to study the influence of nitrite contents, water-cement ratios, mineral admixtures (fly ash and ground slag), cuing temperatures and curing ages on the content of free nitrite ions in cement paste. In this study the content of free nitrite ions in cement paste was measured by the visible spectrophotometer. Moreover, x-ray diffraction was used to research the characteristics of hydration products of the cement paste. Results showed that a new crystalline phase (${{NO}_2}^{-}$ [Ca₂Al(OH)₆](SO₄)0.3 · 3H₂O) in the cement paste containing nitrite was formed. Additionally, this new crystalline phase dispersed uniformly in the paste. Higher water-cement ratios led to more ${{NO}_2}^{-}$ in solid phase and less ${{NO}_2}^{-}$ in liquid phase. The content of ${{NO}_2}^{-}$ in the cement paste increased with the increasing nitrite content. The addition of fly ash and ground slag reduced the amount of 3CaO · 2SiO₂ · 3H₂O (C–S–H) gel leading to decreasing the adsorption effect and solidifying rate of ${{NO}_2}^{-}.$ The free ${{NO}_2}^{-}$ decreased rapidly with the increasing curing temperatures when curing ages were lower than 14d. While, nitrite ions decreased slowly with increasing curing temperatures when the curing ages were higher than 14d. The content ${{NO}_2}^{-}$ of all groups decreased with curing ages. (paper)