Enhancing the properties of alkali-activated slag through dry ice addition: Investigation of hydration products and performance characteristics

To study the effect of dry ice on the performance of alkali-activated binders, we added dry ice to an alkali-activated slag (AAS). The addition amount was set to 5%, 10%, and 15% of the slag mass, depending on the amount of CO2 emitted by the material used in the preparation process. Microscopic experiments were performed to analyze the effect of dry ice on the hydration products of the AAS paste; transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the hydration products. Furthermore, experimental tests for the compressive strength, ultrasonic pulse velocity, and electrical resistivity were performed. The results showed that compared with the content of the overall reaction products, the effect of dry ice on the reaction rate was more evident. The addition of dry ice slowed the hydration of the AAS, and the production of the hydration products, such as calcium aluminum silicate hydrate (C-A-S-H) gels, was significantly reduced in the early stage (1 d). Experiments on the strength showed that adding more than 5% dry ice degraded the early mechanical properties of the AAS. However, the mechanical properties of the AAS with dry ice added in the middle (3 and 7 d) and late (28 d) stages rapidly improved because the dry ice was added to the AAS to form potassium and calcium carbonate. In the middle (3 and 7 d) and late (28 d) stages, CO32- underwent a carbonation reaction to form carbonate compounds, enhancing the mechanical properties of the AAS.