Cement clinker production also generates considerable quantities of process dusts, e.g. bypass dusts. The composition of the dusts can also vary within a plant depending on the operating conditions. The relevant constituents include alkali sulphates and chlorides as well as carbonates, free lime and clinker phases. As a minor constituent, chloride-rich dusts can only be used to a very limited extent for cement production due to the low chloride limit, whereas dusts containing sulphates can be used up to 5 wt.%.
The focus is on investigating the suitability of sulphate-rich process dusts as a minor constituent for sulphate optimisation. The aim is to examine whether and how early strengths can be improved and the clinker content reduced, particularly in cements with several main constituents. Increased use of sulphate-rich process dusts could substitute proportions of natural sulphate carriers (anhydrite, gypsum).
Isothermal heat flow calorimetry records the heat release of the cements over time during the hydration processes. Depending on the main cement constituent, optimal hydration requires different availability of the sulphates. Whether and how these are available is to be understood by tracking the hydration heat release. From the comparison with the usual methods for sulphate optimisation, such as strength and workability tests, it will be determined whether isothermal heat flow calorimetry can be used as a fast, simple and cost-effective optimisation method.
The investigations will be carried out on the most common types of cement with several main constituents, on cements containing blastfurnace slag and limestone (CEM III/A, CEM II/B-M (S-LL), CEM II/A-LL, CEM II/B-M (Q-LL). Isothermal heat flow calorimeters are already used today by many cement manufacturers to determine the heat of hydration. Therefore, the results can be used directly by SME in the cement industry for a more efficient use of main and minor cement constituents.