Subject matter

The most suitable path to achieve sustainability in cement production is the reduction of the clinker factor by adding Supplementary Cementitious Materials (SCM). The most common SCMs used today are fly ash, slag, and natural pozzolan. The reduction of steel production and phasing out of coal power plants has reflected in a significant decrease in the supply of these common SCMs, which represent less than 10% of the global cement production.

The scarcity of common SCMs has prompted the use of calcined clays as an alternative. Calcined clays have been used for decades as pozzolans. Recent developments have shown that clays containing at least 40% of kaolinite as main clay mineral can be highly reactive if properly thermally activated. If limestone is added into the cement – calcined clay blend, the synergy between the two SCMs enables higher clinker substitution, with an improved performance both in terms of mechanical properties and durability.

There is a growing number of research groups working on the subject of calcined clays in Europe, Asia and Latin America. Further, a significant amount of clays from around the world has been characterized. The integration of this work into pre-standards will pave the way for a wider usage of the material.

Terms of reference

The TC is supposed to run for 4 to 5 years

Members will be recruited from academia and industry, based on their experience in the use of calcined clays, with the capacity to carry out round robin testing with no outside funding.

The work will be focused on every issue related to the use of kaolinitic clays for the production of reactive pozzolans through their thermal activation and their use in cement manufacture. This includes clay mineralogy, geology of clay deposits, the use of calcined clays in Portland-calcined clay and Portland calcined clay-limestone systems, hydration and performance of calcined clays in cementitious systems.

Detailed working programme

- Start-up meeting: introduction of members, suggestion of new members, overview of members’ competences and experience, plan of activities, organisation of initial workshop

- Workshop for the members, to agree upon a work plan. The main areas of interest and the partner willing to investigate on them will be determined. There will be three sub-groups: (i) kaolinitic clay geology and mineralogy, (ii) the process of clay thermal activation, and (iii) use of calcined clays as SCM in cementitious systems

- A partial report will be issued after 12 months, with reports on the three main areas described. Then the main areas to continue will be decided and the new workplan will be agreed upon.

- International conference on calcined clays (2019)

- Regional seminars in Latin America and Asia, coupled with short courses

- Summary of TC findings in one or more journal publications

- Proposal of pre-standard.