Industrialisation of calcined clay cements: past, present, and future

Taking inspiration from the recent rise in interest on calcined clays, the RILEM technical committee RILEM TC 282-CCL on Calcined Clays as Supplementary Cementitious Materials has been summarising knowledge on a wide variety of topics related to the use of calcined clays in cement and concrete. In this article, the working group 2 of this committee summarises recent global efforts on the industrialisation of calcined clay cements, to bring the work of the committee into context. Clays have been a key construction material since Roman times but are now designated as crucial for enhancing cement industry sustainability in the short to midterm. Several industrial and semi-industrial trials that have recently produced calcined clays through various techniques, such as static, rotary, and suspension calcination technologies are covered in this paper, while worldwide cement production trials with calcined clays and limestone are also discussed. Major projects considering local clays as construction materials are presented as examples of global interest in the subject. Due to interest in achieving climate goals, calcined clays are being rapidly reintroduced into the cement industry, and academic research has played an important role in this process. The examples discussed in this article demonstrate the importance of greater and swifter knowledge transfer from academia to industry. The work also demonstrates the need to upgrade industrial equipment and design new efficient equipment to eliminate the use of fossil fuels for clay calcination, a process that requires relatively lower temperature than clinker production. The challenges in achieving net-zero carbon emissions in clay calcination technologies are also discussed. Overall, this paper presents the context in which the RILEM TC 282-CCL operated.