Conference Agenda

In Paris in 2015, 195 nations committed to a legally binding agreement to cut greenhouse gas emissions by 43% by 2030 — relative to a projected 2025 peak — in pursuit of limiting global warming to 1.5°C. Among the sectors standing in the way of that target, cement manufacturing occupies an uncomfortable position: responsible for roughly 8% of global anthropogenic CO₂ emissions, yet widely classified as "hard to abate." The industry faces mounting pressure to decarbonize, even as the chemistry of its core product makes that task uniquely difficult.

This talk examines the CO₂ emissions embedded in the production of Ordinary Portland Cement clinker through a geoscientific lens, tracing emission sources to their mineralogical and thermochemical roots. It also makes the case for cement itself — a material of extraordinary performance whose role in modern society, from infrastructure to housing, is neither shrinking nor optional.

Against this backdrop, the talk surveys the strategic landscape. The IEA's 2018 Technology Roadmap for Low-Carbon Transition in the Cement Industry provides a framework largely shaped by industry initiative. More recently, publicly funded research in Germany has accelerated, supported by EU NextGenerationEU funds, BMBF/DLR programs, and DFG Priority Program 2436 – Net-Zero Concrete.

Drawing on two research projects, the talk presents novel pathways toward low- and zero-carbon binders. Low-calcium cements from recycled concrete fines, hardened through controlled carbonation, demonstrate substantial reductions in embodied CO₂. Serpentine-derived binders, meanwhile, show promise not only for carbon-neutral concrete but for active CO₂ sequestration beyond the system boundary.

The rising demand for concrete increases concrete waste and CO₂ emissions from cement production. Mineral carbonation offers a dual benefit: reducing the cement industry’s carbon footprint by capturing CO₂ in long-lasting mineral phases and recycling cement as a supplementary cementitious material (SCM). First studies of OPC mixed with carbonated cement paste (cCP) already give promising results concerning its use as SCM.

In this study, various cCPs – including cCPs made from different CEM I’s and cCPs from OPC containing conventional SCMs – were characterized with several methods and tested for their reactivity first. The main focus was on the early hydration of the OPC-cCP mixes, investigated by in-situ XRD and heat flow calorimetry. The presence of cCP affects especially the phase development and heat flow evolution in the first hours of hydration by e.g. a higher precipitation rate of ettringite. Additional Imeter hardness measurements revealed a correlation between ettringite precipitation rate and hardness evolution during that time. Secondly, the use of cCP made from OPCs with a variable chemical composition was investigated revealing a dependence of the hydration behaviour not on the initial OPC chemistry but rather on the physical properties in case of the cCPs made from various CEM I’s. With cCP containing conventional SCMs pore analyses show an influence of the chemical composition on the hydration kinetics, though. In summary, we provide new insights into the hydration kinetics of OPC–cCP mixes, supporting the advancement of cCPs as viable future SCMs.

Reducing the clinker factor in cementitious materials is one of the key challenges in achieving more sustainable mortar and concrete production. At the same time, many construction applications still demand fast early setting, leaving little room for conventional clinker reduction strategies. For decades, the hydration of C₃A has been treated as a largely fixed process: little initial reaction followed by a comparatively limited reaction extent during the first hours of hydration. Therefore, a substantial fraction of the early hydration potential of C₃A has remained fundamentally unused. This work breaks this long-established concept by demonstrating that the early C₃A reaction can be fundamentally intensified. The use of triethanolamine (TEA) enables a profound acceleration and activation of C₃A hydration, resulting in reaction degrees approaching 90% at very early ages. Simultaneously, this high hydration degree of C₃A can be combined with additional sulfate content resulting in two beneficial effects: 1) Further dilution of the cement and 2) dramatically increased ettringite precipitation. This enhanced ettringite formation leads to very fast setting despite the lower clinker content. These findings demonstrate that the traditionally “static” understanding of OPC hydration can be fundamentally reconsidered. Unlocking this previously unused reaction potential opens a new pathway toward low-clinker binder systems.

The alkali activation technology (AAT) for inorganic polymer formation is a mature technology penetrating the market for a possible substitution of Portland cement (PC). This will strongly reduce the CO₂ emission compared to the use of PC. The AAT requires alkali-silicate solution mixed with metakaolin, including calcined laterites, and waste materials like fly ash or slag. These ingredients form the binder for obtaining mortars and concrete. It has been shown that the addition of slag significantly increases the flexural and compressive strength in the range of typical high-performance concrete applications. Green routes for the alternative preparation of alkali silicate solutions are under investigation. Meanwhile, there are arguments put forward by the “PC suppliers” that their CO₂ footprint is improved with the additions like slag, fly ash and metakaolin, too. It will be shown that PC based binders and those from AAT are structurally equivalent possessing the same binding properties. New strategies on the market also include the use of accelerated re-carbonated fine crashed waste concrete as substitute in part for sand and gravel in order to preserve natural resources and store a significant portion of CO₂. Actually, the total Ca-O content brought in for the binder can be re-carbonated in any waste concrete and mortar.