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CONCRETE PRODUCTS & CAST STONE68 CPI %u2013 Concrete Plant International %u2013 4 | 2025 www.cpi-worldwide.comAgainst the backdrop of a globally projected annual cement production of approximately 6 billion tons by 2050, a key question arises: to what extent can clinker be replaced by alternative materials? The current share of Portland cement stands at around 24% and is expected to be reduced to about 10% by 2050 as part of this development. It is important to note, however, that potentially reactive composite materials such as coal fly ash and ground granulated blast furnace slag (GGBS) are only available in limited quantities. Globally, fly ash is generated at a volume of approximately 700 million tons per year, while GGBS amounts to about 300 million tons per year. Both material streams are subject to considerable economic and seasonal fluctuations. Moreover, it is already foreseeable that their availability will decrease significantly in the future. In the case of GGBS, this is due to the steel industry%u2019s transition to hydrogen-based direct reduction and increased recycling activities. The supply of coal fly ash is declining as a result of the global phase-out of coal and improvements in flue gas cleaning efficiency.Against this background, the identification and evaluation of alternative mineral materials as potential filler components in concrete production is gaining increasing importance. In this context, the present study examines a residual material from tin tailings at the Ehrenfriedersdorf site in Germany for its suitability as a pozzolanic or inert filler [2]. One of the two tailings ponds in Ehrenfriedersdorf contains around 3 million tons of material, offering significant potential for resource-efficient use in construction applications.Legal and technical framework for the use of tailings as a mineral substitute in constructionThe German regulation for substitute building materials was approved in 2021 after years of technical and political deliberation. It came into force on August 1, 2023, and has since provided a nationwide framework regulating the use of mineral substitute building materials in construction projects related to roads, railway infrastructure, and paved storage or traffic areas. The regulation aims to enable the environmentally sound and legally compliant reuse of mineral waste as a substitute construction material. However, tailings that are still classified as waste under the German Circular Economy Act do not fall under the scope of the regulation.Since different applications require scenario-specific threshold values, it is not possible to make a general statement Utilization of tailings in the production of concrete paving blocksNew industrial by-productsn Ferdinand Senf, Henrik Funke and Sandra Gelbrich, Technical University Chemnitz, Germany01020304050607080901000,1 1 10 100Cumulative distribution Q3(x) (%)Particle size (%u00b5m)x50 = 19.2 %u00b5mMineral Ma%Quartz 38.8Muskovit 19.0Biotite 10.2Plagiograde 12,2Fluorite 1.0K-Feldspar 5.3Topaz 3.7Chlorite 8.0Kaolinite 1.7x90 = 69.2 %u00b5m01020304050607080901000,1 1 10 100Cumulative distributionQ3(x) (%)Particle size (%u00b5m)x50 = 19.2 %u00b5mMineral Ma%Quartz 38.8Muskovit 19.0Biotite 10.2Plagiograde 12,2Fluorite 1.0K-Feldspar 5.3Topaz 3.7Chlorite 8.0Kaolinite 1.7x90 = 69.2 %u00b5mFig. 1: Particle size distribution and mineralogical composition.