Performance evaluation of alkali-free accelerators with different supplementary cementitious materials

Alkali-free liquid accelerators (AS) are critical components in shotcrete applications, with their compatibility with mineral admixtures playing a pivotal role in determining concrete performance. This study systematically investigates the adaptability of AS to fly ash (FA), slag (SL), and silica fume (SF) by evaluating key performance indicators, including setting time, compressive strength, and autogenous shrinkage. The results demonstrate that as the content of FA and SL increases from 10.0% to 30.0%, the setting time is progressively extended. In contrast, the setting time is reduced with increasing SF content, ranging from 5% to 15%. Higher FA content leads to a gradual decline in both 1-day and 28-day compressive strength. For SL, the 1-day strength decreases with higher content, while the 28-day strength initially increases before declining. This behavior is attributed to SL’s reaction with Ca (OH) 2 to form secondary hydration products, whereas excessive SL content limits this reaction, increases porosity, and ultimately reduces strength. SF, on the other hand, significantly enhances both 1-day and 28-day compressive strength due to its high reactivity and fine particle size. Furthermore, FA and SL are shown to reduce autogenous shrinkage, while SF increases it, primarily due to its accelerated hydration and refined pore structure. These findings provide valuable insights for optimizing the proportion of AS and mineral admixtures in shotcrete, offering a theoretical basis for improving performance and durability in practical engineering applications.