The role of clinker substitutes in the cement manufacturing process is becoming more and more important. This is due on the one hand to the increasing demand for high-performance cements, and on the other hand to considerations of economy and CO2 emission reduction. The only widely available materials with latent-hydraulic or pozzolanic properties are granulated blast furnace slag and fly ash from hard coal fired power stations. However, the usage of these materials in the cement industry varies greatly in the different countries of the world. Western Europe is a leading user.