Sulphates in completely recyclable concrete and their effect on the clinker mineralogy

Although concrete is a durable material, it has a big impact on the environment due to its high production volumes. This impact is mostly related to the consumption of virgin raw materials, the production of waste and the emission of carbon dioxide. To optimize the recycling opportunities of concrete, Completely Recyclable Concrete is designed as a raw material for clinker production, without the need for ingredient adjustments. However, CRC concrete constructions may be exposed to environments rich in chlorides, sulphates and other ions, affecting the clinkering process of CRC rubble. Therefore, it is important to know the effect of these ions on the mineralogy of CRC clinker. In this study the effect of sulphate additions to CRC raw meals on the final clinker mineralogy was studied by XRD/Rietveld analysis. It was found that an increasing sulphate content stimulates the formation of CaO containing sulphates such as calcium langbeinite and anhydrite. Additionally SO3 was found to stabilize belite at the expense of alite