Unlocking Nano-CSH and Silica Fume to Enhance the Performance of Alkali-Free Liquid Accelerators in Low-Temperature Environments

This article is based on the research background of an early performance of shotcrete under low-temperature environments. Silica fume (SF) (silicon powder) and nano-CSH are used to improve the effect of the low-temperature environment on the performance of alkali-free (AF) liquid accelerators and early strength of shotcrete. The results show that the 10% SF and 3% nano-CSH composite admixture significantly enhances AF accelerators' performance at 5 °C, reducing initial and final setting times to 3.0 and 10 min, respectively, while substantially improving the early age compressive strength of shotcrete. Furthermore, hydration calorimetry, phase analysis, and microstructural characterization reveal that nano-CSH synergistically enhances silica fume nucleation efficiency.