The last production step in cement manufacturing is the grinding of cement clinker and other constituents. This is especially significant because decisive optimisations are possible at this stage: So-called grinding aids and performance additives can be applied. These achieve a considerable effect with a very low dosage.

Grinding additives serve to optimise the actual grinding process but can also have a performance-enhancing effect on the cement itself, while performance additives specifically influence certain properties of the cement. These include, for example, the water demand and the early and final strength of the cement.

Positive effects

Regarding the sustainability of the grinding process, grinding aids have various positive effects. They can increase the grinding efficiency of the mill by up to 30% and thus reduce energy consumption. They prevent agglomeration of the cement particles, reduce build-up in the mill and increase throughput. An extra effect is a higher grinding fineness, which increases the chemical reactivity of the grinding material.

Among other things, the performance additives enable better dispersion of the cement particles, which means that less water is needed for concrete production. They can also influence cement hydration, which results in higher early and final strengths. As a result, the full performance spectrum of the cement clinker contained can be exploited – and less cement clinker is needed in the mix overall. This is relevant because cement clinker is particularly CO₂-intensive and can then be replaced by higher proportions of more sustainable components such as limestone powder, granulated blastfurnace slag or pozzolana.

In figures

In a calculation example of a ball mill with a consumption of 4,000 kW, 95 tonnes of cement can be ground in one hour without grinding aids, resulting in an energy consumption of 42.1 kWh per tonne. With grinding aids, the mill manages 116 tonnes and thus consumes only 34.5 kWh/t – an energy saving of 22 %.

Performance additives generate CO₂ reduction effects by reducing the cement clinker content, which accounts for approx. 700 kg of CO₂ equivalents per tonne. In practice, for example, instead of a distribution of 65 % cement clinker, 25 % granulated blastfurnace slag and 10 % limestone powder, 50 % cement clinker, 30 % granulated blastfurnace slag and 20 % limestone powder can now be used – with the same performance characteristics. The saving amounts to 120 kg CO₂ equivalents per tonne of cement.

Conclusion

Modern cement additives can both make the cement manufacturing process more efficient and help optimise cement composition towards lower CO₂ emissions.