*Proceeding Paper* **Increasing the Pozzolanic Reactivity of Recovered CDW Cement Stone by Mechanical Activation †**

**Roland Szabó \*, Máté Sz ˝ucs, Mária Ambrus and Gábor Mucsi**

Institute of Raw Material Preparation and Environmental Processing, University of Miskolc, Egyetemváros, 3515 Miskolc, Hungary

**\*** Correspondence: roland.szabo@uni-miskolc.hu

† Presented at the 10th MATBUD'2023 Scientific-Technical Conference "Building Materials Engineering and Innovative Sustainable Materials", Cracow, Poland, 19–21 April 2023.

**Abstract:** The study focuses on enhancing the reactivity of the fine size fraction of construction and demolition waste (CDW) by mechanical activation in a stirred media mill. Systematic measurements were carried out to monitor the change in cement stone reactivity. The fine size fraction of CDW (<200 μm) was milled in a stirred media mill for 1, 3, 5, and 10 min. The dispersion characteristics (particle size distribution, specific surface area (SSA)) of the mechanically activated CDW powder were determined using a laser particle size analyzer. Changes in the structure of the mechanically activated CDW powder particles were determined by Fourier transform infrared spectroscopy (FTIR) measurements. The effect of the mechanical activation on the pozzolanic reactivity of CDW powder was measured by lime sorption test and compressive strength measurements. The results clearly show that Portland cement can be replaced with mechanically activated CDW powder; however, increasing its amount decreases the strength. Furthermore, the grinding fineness significantly influenced the pozzolanic reactivity of the mechanically activated CDW powder, and thus the strength of the specimens. The CDW powder milled for 10 min had 51% more lime uptake than the initial CDW sample, and the specimen strength at the age of 7 days was 23% higher using ground CDW powder than using initial CDW at a 20% cement replacement ratio.

**Citation:** Szabó, R.; Sz ˝ucs, M.; Ambrus, M.; Mucsi, G. Increasing the Pozzolanic Reactivity of Recovered CDW Cement Stone by Mechanical Activation. *Mater. Proc.* **2023**, *13*, 27. https://doi.org/10.3390/ materproc2023013027

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and Izabela Hager

Published: 15 February 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

**Keywords:** construction and demolition waste; cement substitution; mechanical activation; stirred media mill; reactivity
