In an effort to tap the further potential for CO2 reduction, HeidelbergCement Technology Center (HTC) has been working on the development of alternative binders and and it now believes that one of the most promising concepts is a calcium sulfoaluminate-belite binder (CSAB).
Calcium sulfoaluminate (CSA) cements have been produced for use in building chemicals for a long time, especially in China, HTC explained in a statement released yesterday. CSA cements are mainly used in screeds, tile glues, and special products. A characteristic feature is that they form ettringite very quickly and therefore exhibit a very high early strength. Experiments have already been performed with a view to use these cements for construction purposes, but their durability has not yet been sufficient, HTC states.
Nonetheless, Dr Wolfgang Dienemann, Director of Global Research & Development HTC, sees a worthwhile approach: “If we combine CSA cements and their high early strength with belite (dicalcium silicate), the slow-reacting clinker phase in classic Portland cements, it might be possible to combine the advantages of both systems in one cement. The ettringite formation is responsible for the early strength, while belite hydration – as with Portland cement – leads to calcium silicate hydrates, which form a permanent and durable structure. This combination seemed promising enough to us that we continued working on it.” ??In 2010, the researchers at HTC started investigating the cement chemistry of CSAB under various process conditions. Dienemann: “For the first time, we looked more closely at the ternesite clinker phase, which was considered to be non-reactive until now. This phase does not react with pure water, but if the pore solution contains aluminium, there occurs an immediate chemical reaction and a solid structure is formed.” After the first successful burning tests in the lab, HTC registered two patents for the manufacturing of clinker containing ternesite (Belite Calciumsulfoaluminate Ternesite - BCT) in the late summer of 2012, and four patents for applications using ternesite containing clinker in various binder systems (= cement types).
Because of its chemical composition and manufacturing at lower temperatures, the new product generates up to 30 per cent less CO2 than normal Portland cement clinker. There is also an improvement in energy efficiency, as the burning temperature is 150-200°C lower and the fuel consumption is reduced by about 10 per cent. The electricity costs for the manufacturing process are likewise lowered by about 15 per cent, because less energy is required, particularly for the grinding process.
The next steps…
Dr. Wolfgang Dienemann describes the next steps at HTC as follows: “Since the addition of high-quality aluminium carriers such as bauxite is very expensive, we are currently experimenting in alternative trials with the addition of waste materials containing aluminium, e.g. brown coal fly ash and other slags. In addition, the use of other industrial by-products, such as FGD gypsum, could also be considered.”
The first large-scale trial is planned for this year in one of the German HeidelbergCement plants, where the new products are to be manufactured for the first time with the existing plant technology.