Structure characteristics and composition of hydration products of coal gasification slag mixed cement and lime

In order to extend the utilization of slag in concrete, it is a key to understand the reaction mechanism of coal gasification slag with cement or lime. This article focus on the characteristics of gasification slag and hydration products of slag with cement or lime by analyzing microstructure, elements, mineral composition and slag mortar strength. The microstructure and composition were determined by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) and X-ray diffractometry (XRD). The results show that the content of residual carbon in the fine slag is evidently more than that of coarse slag and residual carbon hinders the cementitious reaction between slag and cement or lime. In addition, many hydrated products, such as ettringite, okenite and C-S-H gels, are detected in the mortar mixed coarse slag, which indicates that there is positive interaction between the coarse slag with the cement. The abundant active mineral phases in the coarse slag can facilitate the cementitious reaction, and enhance the mortar strength. It is also found that the lime can effectively activate the SiO2 and Al2O3 mineral phases in the coarse slag to form hydration products, and the calcite from hydration reaction is favorable to improve the strength of mixtures.