Page 31 - Demo

AAC WORLDWIDE %u2022 2.2026 SCIENCE & INNOVATION 29AAC powder and granulateAAC construction and demolition waste of various density class and age were investigated. The compressive strength was determined from small cubic specimen (30-50 mm) after drying at 105%u00b0C. The bulk density of the crystallite matrix was determined by combining the air porosity quantified by micro-CT and the skeletal density determined by helium pycnometry. It was additionally determined from the water absorption of the AAC powder after water saturation for at least 24 h and vacuum filtration at < 0.1 bar for 30 min [9]. The bulk density of the loose powder or granulate was determined by the shovelling procedure without compaction [8].Several methods for size reduction were investigated. The suitability of each method depends on the desired particle size distribution. A coarse granulate was obtained by a jaw crusher or single-shaft shredder. A fine powder was obtained by a screen ball mill, a disc mill or the %u201cecopulser%u201d, a novel size reduction technology based on shock waves. After size reduction to less than 1 mm %u2013 such as for lightweight gypsum-based building plaster %u2013 most of the air porosity is lost. The easiest parameter to collect for quality control is the powder bulk density, which correlates with the density of the AAC crystallite matrix. The lowest density class exhibits the most porous crystallite matrix and yields a lightweight powder with a bulk density below 500 kg/m%u00b3 (Table 1). Even older AAC with higher density classes yields a sufficiently lightweight powder, as the density of the crystallite matrix is only slightly higher. The same applies to coarsely crushed AAC granulate < 4 mm (Table 2) used in gypsum-based self-levelling mortar, except Dipl.-Ing. Frank Hlawatsch is a scientific researcher in materials testing in the field of civil engineering at Leibniz Institute for Materials Engineering in Bremen, Germany. He has studied Civil Engineering with the focus on building materials at the university of Weimar, Germany. He is currently working on recycling and reuse of demolished construction materials. He also is managing director of the research association \ of materials in construction industry).Karsten Mesecke has a background in chemistry and chemical engineering. He dedicated his PhD to autoclaved aerated concrete and in specific to the phase formations under hydrothermal conditions. His current research focuses on the recycling of AAC and the molecular structure of C-S-H. mesecke@mpa-bremen.deRobert-Balthasar Wudtke is a professor of geotechnical engineering and head of the Thuringian Innovation Centre for Recyclable Materials (ThIWert) at Fachhochschule Nordhausen (HSN). He is a certified expert in the field of earthworks and foundation engineering and currently serves on various national and European standardisation committees as a member or chairman. As part of his employment as a research assistant at the Chair of Foundation Engineering at the Bauhaus University Weimar, he worked on and completed various research projects between 2004 and 2016 on the topics of %u2018Identification of material properties of cohesive soils under the influence of variable water contents%u2019, %u201cTailings%u201d, %u2018Hydraulic ground failure%u2019 and %u2018Causes of foundation damage%u2019. In 2014, he completed his doctorate at the Bauhaus University Weimar on the topic of %u2018Hydraulic heave in cohesive soils%u2019.Katrin Schmidt graduated from Hochschule Nordhausen (HSN) in Environmental and Recycling Technology with a specialization in process engineering. She gained professional experience as a project manager responsible for the mechanical comminution and classification of raw materials. Since 2011, she is a research associate at Hochschule Nordhausen and following the establishment of the Thuringian Innovation Center for Secondary Raw Materials (ThIWert) in 2019 her focus is sustainable construction.Daniel Ufermann-Wallmeier studied civil engineering at Fachhochschule M%u00fcnster and received his doctorate from Bauhaus University Weimar with a dissertation on alkaline-activated binders. He was professor of building materials technology at Fachhochschule Bremen and co-chair of the Bremen Materials Testing Institute, a division of Leibniz IWT Bremen, from July 2019 to August 2025. Now, he is professor of building materials technology in the Department of Architecture at Fachhochschule Dortmund.