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The durability of mortar and paste mixtures with respect to chloride ion ingress was investigated for binary blends of Portland Cement Calcined Clay, and ternary systems of Limestone Calcined Clay Cement (LC 3). Five clays from various sources with different kaolinite content (17-95%) were studied. The main factor controlling the diffusivity of LC 3 systems was found to be the kaolinite content of the clay. Resistance to chloride ingress increased to intermediate levels of kaolinite content and then stabilized. An intermediate kaolinite content of around 50% resulted in two orders of magnitude reduction in diffusivity compared to PC, indicating that the use of high grade (expensive) clays is not necessary to obtain good durability. The chloride binding capacity and distribution of bound chloride between Friedel's salt and C-AS -H were quantified for the different systems at fixed water to binder ratio of 0.5. The chloride binding capacity appeared to be a minor factor compared to the porosity refinement in the improved durability of LC 3 systems.

This paper details the main factors influencing the performance of limestone calcined clay cements (LC3). The kaolinite content plays a major role in the rheological properties as well as strength development. Even in the presence of secondary phases, kaolinite can be accurately quantified by thermogravimetric analysis. The performance of LC3 is slightly influenced by the calcination process of clay, but it can be optimized by using the correct calcination temperature and applying a specific mix design with adjusted sulfate and alkali content. The hydration reactions of LC3 are fully characterized. They vary slightly from plain cement. There is no significant change in terms of phase assemblage. The main properties of LC3 are also described. LC3 blends show a lower creep compliance and a delay in shrinkage strains compared with plain cement. Concerning durability, LC3 blends show outstanding performance with respect to resisting chloride ingress and expansion from the alkali–silica reaction.

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.

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Although supplementary cementitious materials (SCMs) are now commonly accepted and widely used, consensus has not been reached for methods to test their chemical reactivity.A multitude of test methods exist but often fall short on one or more of the key features of a proper test, i.e. width of scope, practicability, reproducibility, and relevance of the result.A rapid, robust, and relevant chemical reactivity test applicable to a wide range of SCMs would therefore not only serve as global benchmark, it would also remove present ambiguities as regards to classification.In response a new, so-called R3 test was conceived at EPFL and is now being further developed and tested in RILEM TC 267 TRM " Tests on reactivity of Supplementary Cementitious Materials". The test method was initially based on a screening of calcined clays in portlandite-alkali-sulfate systems by isothermal calorimetry. Subsequently the system formulation was more systematically studied and compared to strength development of blended cement mortar bars for a wide range of calcined kaolinitic clays.Remarkably good correlations between strength development and heat release were found. This was confirmed for other SCMs, and other measurable system properties. In particular, bound water content and chemical shrinkage correlated remarkably well to the isothermal calorimetry results. The origin of this correspondence can be traced back to the hydration reaction. Indeed, it is the solidification of water that directly links heat release, chemical shrinkage, and, obviously, bound water content. This contribution traces back the origins and the first inroads leading up to the present state of development of the test method and concludes on future perspectives.