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CONCRETE TECHNOLOGYwww.cpi-worldwide.com CPI %u2013 Concrete Plant International %u2013 4 | 2025In the research project RTTS, funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK), new approaches for the production of resource-efficient and CO2-reduced tubbing elements and joint-filling grout were investigated and developed. Various concrete technology optimization strategies were devised and examined to produce concrete with optimized sustainability characteristics. All of these approaches aimed at achieving a CO2 footprint reduction of up to 60% compared to the CEM I reference mix, while maintaining comparable technical properties, such as high early strength and adequate carbonation resistance.This article describes the different concrete technology optimization approaches and focuses on presenting and discussing the results related to early strength development.The RTTS research network includes the companies Ed. Z%u00fcblin AG, Master Builders Solutions Deutschland GmbH, Dyckerhoff GmbH, as well as the Research Association for Tunnels and Transportation Infrastructure (Studiengesellschaft f%u00fcr Tunnel und Verkehrsanlagen, STUVA e. V.), and the Institute for Building Materials at Leibniz University Hanover (Fig. 1).Concrete technology optimization approachesIn the RTTS research project, various concrete technology optimization approaches were investigated for the production of resource-efficient and CO2-reduced tubbing elements. At the binder level, three different optimization strategies were examined in combination with accelerating admixtures (Fig. 2). The primary focus of the two binder approaches was the reduction of clinker content and the substitution with reactive constituent materials that have significantly lower CO2footprints. Both a binder based on calcium sulfoaluminate cement (CSA cements) [15] combined with blast furnace slag cements (CEM III), as well as granulometrically optimized ternary binders consisting of clinker, slag, and limestone powder [10, 16], were investigated. These binder types were complemented by specially developed and tailored retarding admixtures when using CSA cements, and by accelerating admixtures when using the strongly clinker-reduced ternary binders.Fig. 1: The RTTS research network.