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Promoting performance in low clinker cement

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World Cement,

Emanuele Gotti and Davide Padovani, Mapei SpA., review a new series of additives designed to enhance the performance of low clinker cements.

In recent years, the cement industry has been forced into a change unlike any before in its long history. Phrases like ‘green economy’, ‘CO2 reduction’, ‘digitalisation’, ‘zero emissions’, ‘carbon neutral’, etc., that once applied to other sectors of industry are now core components of any cement producer’s strategy.

In fact, the production of cement is one of the most significant sources of CO2 emissions, and is estimated to contribute 8% of global emissions. These emissions are produced in part by the decarbonisation of calcareous minerals used for the production of clinker, but also by the large quantities of fuel necessary to reach high temperatures. Overall, it is estimated that for each ton of clinker, approximately 0.84±0.10 t of CO2 is produced and emitted into the atmosphere.

To achieve the goal of carbon neutrality by 2050, the cement industry is implementing a range of measuress. These include, for example:

  • Increasing the use of alternative fuels.
  • Reducing the clinker-to-cement ratio.
  • Using natural gas and hydrogen fuel.
  • Using alternative raw materials.
  • Implementing carbon capture technology.
  • Using renewable energy sources.
  • Improving energy efficiency.
  • Sourcing local supplies.
  • Using green methods of transportation.

In addition to this scenario, the Covid pandemic and the ongoing crisis in raw materials/logistics has pointed out the fragility of the traditional cement industry. When considering the effects of this challenge on the main product of the cement industry – the cement itself – the following steps can be distinguished:

  • 1. A moderate clinker reduction (3 – 5%) in traditional cement types, by using high quality cement additives to boost strengths.3,4 In this area, even in the best cases, there is still a further 2 – 3% clinker to be reduced according to current standards. This is a short-term approach, mainly based on immediate savings.
  • 2. The switch from the traditional CEM I and CEM II (limestone) cements to the more sustainable CEM IV pozzolanic cements, ideally with natural pozzolan. In addition to the environmental and economic benefits associated with lower clinker/cement concretes produced with pozzolanic cements, these cements also display enhanced properties such as greater resistance to external attacks and greater durability.5 But can CEM IV fit with all the uses in concrete? A key limiting factor is that natural pozzolan is only available in a few countries and it is now clear that alternatives are not easily available: good quality fly ash and slag are expensive and not going to be available in sufficient quantities in the near future.
  • 3. The cement industry, in response to points 1 & 2, has introduced completely new types of cement containing significantly less clinker than before (on average 50% of clinker compared to the current 65 – 70%), together with new standards (e.g. EN 197-5) to regulate these new cements. Examples include limestone-calcined clay cements and all the cements based on a similar chemistry (the activated pozzolanic reaction) containing ‘recycled’ materials.

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