Study on the effect of supplementary cementitious materials on the volume stability of mortar mixed with laboratory-made high-content fluorine-type accelerator

The high-content fluorine-type accelerator (AF) can be prepared from fluorine-containing wastewater due to its low cost and is widely used in many projects. In this study, the fluorine-type alkali-free liquid accelerator was synthesized by simulating fluorine-containing waste liquid in the experiment, and its performance was tested and shown to meet the standard requirements. Subsequently, three supplementary cementitious materials (granulated blast furnace slag-GBFS, fly ash-FA, and silica fume-FS) were used to study the effect of supplementary cementitious materials on the setting time, mechanical properties and volume stability of mortar mixed with accelerators. The results show that the addition of supplementary cementitious materials shortens the setting time of the cement paste, while maintaining the requirements on compressive strength. Among these materials, the incorporation of silica fume makes the best effect of shortening the setting time, and yields the highest increase in compressive strength. In the 180-day test, both FA and GBFS can reduce the autogenous shrinkage and drying shrinkage of mortar, and the shrinkage reduction effect of FA is more prominent. FS significantly increases the autogenous and drying shrinkage of the mortar. By observing the changes to mass and humidity under the drying conditions of mortar, it is found that FS can effectively reduce mass loss and humidity change. This is because the early hydration reaction of FS occurs earlier than that of FA and GBFS, and it can play a role in refining the pore structure. However, the addition of FS aggravated the shrinkage of the mortar by increasing the pore size of 5–50 nm, resulting in higher capillary tensile stress and greater shrinkage driving force. FA increased the mass loss and internal humidity reduction of the mortar, but was less driven by capillary tensile stress due to coarsening of the pore structure. This study provides theoretical guidance for practical construction application. •The effect of SCMs on the volume stability of cement mortar mixed with AF was investigated.•Under standard drying conditions, the effects of SCMs on the mass loss and internal humidity changes of cement mortar mixed with AF were investigated.•The mechanism affecting the volume stability is explored from the aspects of hydration products and pore distribution.