Research on hydration characteristics of OSR-GGBFS-FA alkali-activated materials

Based on the characteristics of alkali-activated materials (AAMs) in energy saving and emission reduction, as well as giving full play to the complementary advantages of multi-component solid waste. In this study, a new type of AAMs was prepared from oil shale residue (OSR), ground granulated blast furnace slag (GGBFS), and fly ash (FA). Compressive and flexural strength tests, fluidity experiments, setting time, heat of hydration, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and Thermo-gravimetric analysis (DTG-TG) were used to analyse the mechanical properties, workability, mineral composition, microstructure, and hydration products of the AAMs. The results showed that the microstructure of AAMs was dense, with high early strength, good mechanical and working properties, and no tendency for retrogressive strength with an increase in the age of maintenance. Under the action of NaOH/Na2SiO3, there is a synergistic hydration of the water-hard and volcanic ash materials, and the three raw materials have synergistic hydration properties and indispensable coupling mechanisms. Meanwhile, the effect of the activator content on AAMs is bidirectional. The OSR, GGBFS, and FA in the AAMs exhibited faster hydration reactions under the action of NaOH/Na2SiO3 and abundant hydration products, which mainly included C-S-H, C-A-S-H, N-A-S-H, and small amounts of CaCO3, hydrotalcite (HT), and Ettringite (AFt). The specimens all met the requirements of the 42.5-grade composite silicate cement, and some specimens reached the strength requirements of the 62.5-grade silicate cement or above. OSR has great potential as a silicate-aluminate material, and this study provides a solid foundation for its further development and utilisation.