Cement industry is facing great pressure to save high-quality fossil fuels and reduce CO2 emissions. At present, there is no new cementitious material that can completely replace Portland cement (Portland cement in China), so the development of low-clinker multi-component Portland cement is undoubtedly an important energy-saving and emission-reduction measure. In 2011, some cement industry research institutes in Germany proposed that the clinker content in Portland cement could be reduced to 50%, and a new type of CEM "X" cement could be developed. After many years of experimental research, it has been formally listed in the European Union cement standard EN197-1. Two new cement varieties with low clinker content are added to the existing 27 standard cement varieties in 5 categories in the European Union.
One is to add a grade C in addition to the existing grade a (the clinker content is 80% -94%) and grade B (the clinker content is 65% -75%) in the class II CEM II, and the clinker content is reduced to 50% -64%, which is marked as CEMII/C-M. It is called Portland-composite cement. The other is to add a large category, namely CEM VI, which is called composite cements. The clinker content in CEM Ⅵ cement is 35% ~ 49%, the granulated slag content is 31% ~ 59%, and the rest components are limestone and coal ash. In the original EN197-1standard, the class V cement CEM V is no longer called composite cements, but is renamed as granulated blast furnace slag-pozzolanic cements (granulated blastfurance slag). At the same time, it is also proposed that in addition to the two new varieties of cement based on the existing traditional components, cement containing a small amount of one or more new components or cement with great differences from the existing standard cement will be developed in the future.
This change in EU cement standards reflects their emphasis on the development of new cement components and new cement varieties. They do not call slag and pozzolan as cement additives or admixtures, but as the main components of cement (content ≥ 5%), because these materials have their own advantages in improving and regulating the performance of cement and concrete. For example, granulated blast furnace slag can improve the late strength of cement and the structural compactness of concrete, but the early strength is low. The addition of finely ground limestone powder can improve the early strength of this kind of cement and prevent the bleeding of concrete, especially when coarse sand and PCE based water reducer are used. Therefore, multi-component and less clinker is one of the development directions of Portland cement. The content and particle distribution of these components should be adjusted according to the performance requirements of cement and concrete, and cement plants should produce and supply more special cement.
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