Development of non-sintered zero-OPC binders using circulating fluidized bed combustion ash

The aim of this study was to develop zero-OPC binders using two circulating fluidized bed combustion (CFBC) boiler ashes with different free-CaO contents. For this purpose, heat of hydration, setting time, compressive strength, microstructure assessment, and thermal analysis tests were conducted to analyze the effect of changing the mixture of zero-OPC binder on the hydration characteristics. Furthermore, the use of mineral admixtures such as fly ash, silica fume, and ground-granulated blast-furnace slag (GGBS) to improve the material's strength was investigated. The hydration products of the zero-OPC binder were ettringite, portlandite, and calcium silicate hydrates components, which are similar to those of existing cements. From the test results, it was found that an optimal free-CaO content of 9.0%-17.0% ensured appropriate compressive strength and setting characteristics. Pre-hydration of CFBC ashes was found to effectively control the amount of free-CaO. The effect of mineral admixtures on improvements in strength confirmed that the CFBC ash-based zero-OPC binder is a highly promising alternative to existing cements.