Against 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’s 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.