The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry’s carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.
The reduction of the clinker factor in cement has emerged as the most promising solution to reduce carbon dioxide (CO2) emissions and to improve sustainability. Limestone calcined clay cement (LC3) is a ternary cement where the synergy between calcined clay and limestone allows the reduction of clinker factors to 0·5. In order to understand practical issues in the production of LC3, such as the selection of raw material and production conditions, industrial production of LC3 has been carried out at three locations in India. A wide range of raw materials was collected from various parts of India and characterised to evaluate their suitability for the production of LC3. Both static and rotary calciners were used for the production of calcined clay. Open- and closed-circuit ball mills were used. Limestones with various impurities and compositions were utilised. It has been observed that lower-grade clay and limestone can be used and that the quality control during the production process can be carried out using widely available techniques. Field trials have shown that the cement can be used without any changes to the existing construction methodologies. This paper discusses the key lessons and insights gained from these trial productions.
The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.