In situ characterization of main reaction products in alkali-activated slag materials by Confocal Raman Microscopy

The re-use of different aluminosilicates, such as blast furnace slag, in the preparation of alternative binders (alkali-activated materials) to Portland cement materials is well document and evaluated by conventional techniques. The use of XRD, FTIR and TG techniques allows obtaining information about the hydration products formed under the conditions of alkaline activation. The formation of the main reaction product (C-A-S-H gel), due to its low crystallinity, is not easily stablished by XRD or FTIR, and it is also quite complex to obtain quantitative information. Confocal Raman Microscopy (CRM) technique reveals information of each of the present phases during the slag activation and in particular. Moreover, CRM provide the evolution of C-A-S-H gel confirming that the growth of the C-A-S-H gel in activate alkaline-systems is different from that an Ordinary Portland Cement system. C-A-S-H gel grows randomly in the regions rich in calcium and silicon. The use of CRM opens a new possibility for the in situ study of complex systems such as the activation of alkali-activated or geopolymers in the search for alternative materials to Portland cement.This work was supported by the Spanish Ministry of Economy and Competitiveness through the Project MAT-2017-86450-C4-1-R and Spanish National Research Council Project NANOMIND 201560E068. Dr. M. Torres-Carrasco is also indebted to MINECO for a postdoctoral fellowship "Juan de la Cierva-Formación" (ref: FJCI-2016-28488). In addition, O. Mikhailova enjoyed a pre-doctoral fellowship with specific junior project FAST-J-18-5568 from the Brno University of Technology (Czech Republic) for internship in Spain