Binary cement pastes from wastes with different substitution ratios: Mineralogical and chemical characterization

The use of different industrial alkaline waste as secondary raw materials (SCMs) is a frequent practice in the cement industry as a source of cements with a lower carbon footprint and thus compliant with the climate neutrality route planned for the year 2050. The present work focuses on the study of alkaline waste from RCDs (fine concrete fraction <5mm, CDW-C), white ladle furnace slag (LFS) and forest biomass ashes (BA). In all wastes, a complete chemical, physical and mineralogical characterization has been carried out using different techniques such as FRX, XRD-Rietveld, SEM/EDX, FTIR, TG/DTA and laser granulometry analysis, in addition to thermodynamically modeling the pozzolanic reaction in the system pozzolan/lime of each of three wastes studied. The binary cement pastes made with partial substitutions of 7% and 20% waste were cured for 28 days under water, and the mineralogical phases formed were analyzed with respect to a reference paste. This analysis has allowed us to highlight that the neophases are related to the nature of the alkaline residue. Generally, in LFS cement paste, hydrogarnet is the stable phase, while in BA and CDW-C pastes, ettringite and C-S-H and C-(A)-S-H gels are the last phases.

Acknowledgments: This research was funded by the Ministry of Science and Innovation of Spain, AEI and FEDER Funds (MICINN, PID2021-122390OB-C21).