CDW Powder Activated by Mechanical, Thermal and Tannic Acid Treatment: An Option for Circularity in Construction

The search for supplementary cementitious materials (SCM), especially from waste, is essential for reducing the clinker/cement factor, promoting circularity and achieving the Net Zero scenario in construction. Construction and demolition waste (CDW) can act as SCM when crushed to powder size. However, as these materials generally have high water absorption and low strength, some particle treatments can improve reactivity or loading effects, maximizing the application potential. In this context, this study aimed to compare the potential between different treatments on CDW powder particles of mixed origin (MP) and concrete (CP) by mechanoactivation (0.5 and 1.0 h), thermoactivation (0.5 and 1.0 h at 800 ℃), and exposure to two tannic acid (0.5% and 1.0%) concentrations. The physical and chemical changes promoted by the treatments were evaluated through analyses of specific mass, surface area, absorption, granulometry, X-ray fluorescence and diffraction, and thermogravimetric analysis. The morphology was verified through electron scanning microscopy. To verify the reactivity of the treated powders, tests were performed on the performance index with Portland cement at 28 days, activity with lime at 7 days, and calcium hydroxide consumption. The treated powders were embedded in pastes with 25% replacement content, and the compressive strength and degree of hydration at 28 days were evaluated. The treatment with 0.5% tannic acid was more effective on concrete powder particles; it densified the powder’s microstructure and improved the filling effect, resulting in an 18% increase in mechanical strength compared to the reference paste. For the mixed powder, mechanoactivation for 1.0 h was more significant in enhancing mechanical strength, leading to a 48% increase compared to the reference. It was found that treatments on CDW powder particles are promising, as they can increase the replacement content of Portland clinker as an alternative in cement composition, thereby promoting the circularity of CDW within the construction supply chain.