Influence of Calcium Nitrite on Physical Properties and Hydration Characteristics of Ferroaluminate Cement–Based Grouting Materials

Abstract To achieve the synergistic optimization of the performance of ferroaluminate cement–based grouting materials using a borax retarder and calcium nitrite accelerator, this study investigated the effects of different calcium nitrite contents on the physical properties and hydration characteristics at a fixed borax dosage (0.28%) through various testing methods. The testing methods included fluidity, setting time, electrical resistivity, internal temperature, compressive strength, drying shrinkage, X-ray diffractometer (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP). The results revealed that calcium nitrite retarded the initial hydration of this system at low contents (0.3% and 0.6%), resulting in a delay in the acceleration period and setting time. Conversely, the hydration was promoted at higher calcium nitrite contents (0.9% and 1.2%), causing an advance in the acceleration period and setting time. The incorporation of calcium nitrite significantly improved the compressive strength from 6 h to 28 days, and reduced the drying shrinkage and mass-loss rates. Microscopic test results showed that calcium nitrite promoted the dissolution of C 4 A 3 S ¯ and the generation of AFt, optimizing the pore structure of the cement pastes. In addition, different calcium nitrite (CN) contents altered the crystal morphology of AFt and contributed to compressive strength by enhancing structural stability and compactness. These results are expected to provide guidance for improving the performance of ferroaluminate cement–based grouting materials by adding calcium nitrite and borax in practical engineering applications.