New insights into the impact of inorganic salt on cement pastes mixed with alkali free liquid accelerator in low temperature

Abstract

Alkali-free liquid accelerators are crucial components of sprayed concrete, and their performance is affected by low environmental temperatures. Therefore, the setting time of the paste is prolonged and the early strength is reduced. In this study, the effect of different types and amounts of inorganic-salt early strength agents on the performance of cement paste mixed with an alkali-free liquid accelerator at low environmental temperatures, was investigated. The results showed that mixing Ca(NO3)2, NaNO3, CaBr2, and NaBr improved the performance of the pastes at low temperatures. Using 1.5% CaBr2 in the mixture showed the most significant improvement in 1 d compressive strength, increasing it from 0.5 MPa to 3.2 MPa and shortening both initial and final setting times. Analysis of the paste hydration products confirmed that nitrate-AFm and bromide-AFm primarily promoted the mixing of an alkali-free liquid accelerator in a low-temperature environment. Therefore, a mechanism for synergetic improvement of nitrate and bromide was proposed.