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In this review by TC- 282 CCL, a comprehensive examination of various facets of chloride ingress in calcined clay-based concrete in aggressive chloride-rich environments is presented due to its significance in making reinforced concrete structures susceptible to chloride-induced corrosion damages. The review presents a summary of available literature focusing on materials characteristics influencing the chloride resistance of calcined clay-based concrete, such as different clay purity, kaolinite content and other clay minerals, underscoring the significance of pore refinement, pore solution composition, and chloride binding mechanisms. Further, the studies dealing with the performance at the concrete scale, with a particular emphasis on transport properties, curing methods, and mix design, are highlighted. Benchmarking calcined clay mixes with fly ash or slag-based concrete mixes that are widely used in aggressive chloride conditions instead of OPC is recommended. Such comparison could extend the usage of calcined clay as a performance-enhancing mineral admixture in the form of calcined clay or LC2 (limestone-calcined clay). The chloride diffusion coefficient in calcined clay concrete is reported to be significantly lower (about 5-10 times in most literature available so far) compared to OPC, and even lower compared to fly ash and slag-based concrete at early curing ages reported across recent literature made with different types of cements and concrete mixes. Limited studies dealing with reinforcement corrosion point out that calcined clay delays corrosion initiation and reduces corrosion rates despite the reduction in critical chloride threshold. Most of these results on corrosion performance are mainly from laboratory studies and warrant field evaluation in future. Finally, two case studies demonstrating the application of calcined clay-based concrete in real-world marine exposure conditions are discussed to showcase the promising potential of employing low-purit

A review of the mechanical property development of concrete containing calcined clay was performed. A comparison of compressive and tensile strength results showed that concrete can be made to have equivalent or higher strength as an ordinary portland cement (OPC) system with up to 30% calcined clay or 50% blend of calcined clay and limestone fines in a limestone calcined clay cement (LC3) system, as long as the kaolinite content in the clay used is above 40%. Most of the strength development in these systems occurs during the first 7 days, making extended wet curing not necessary in these systems. Calcined clay systems are subject to the cross-over effect because of the high solubility of ettringite and lower cement degree of hydration at elevated temperatures. Concrete creep and shrinkage were found to be a function of the clay kaolinite content and replacement level. Bond strength was improved by the use of up to 20% metakaolin.

Materials used in concrete construction are highly regulated through national standards that set minimum material reactivity, composition, and performance. Advances have shown that the combination of calcined clay and limestone fines in cementitious systems can have a synergistic reaction that allows for high levels of clinker replacement while maintaining adequate mechanical properties and durability. Recent modifications to national standards and codes have been made to allow for the use of calcined clay and limestone fines in concrete, albeit with some restrictions on use. Building codes also impose limits such as maximum water-to-cement/binder)-ratio, minimum strength, and minimum cement content as means to meet design service life requirements in lieu of measuring durability properties. This paper reviews the major standards and codes related to calcined clay materials and their use in concrete and suggests changes that could increase adoption and clinker replacement. It is hoped that this review will provide insights that can help facilitate the wider adoption of these materials in the construction industry as well as to identify potential changes in standards or creation of new ones which might be needed to enable the rapid widespread uptake of this promising technology.

This state of the art presents an overview on the effects of calcined clay inclusion on the fresh properties of concrete under the framework of RILEM TC-282 CCL. Progress in recent literature was reviewed to determine the effects of calcined clay, particularly metakaolin and lower grade kaolinite clays, on fresh concrete properties and how to control them using admixtures, particle packing, and mixture proportioning. A summary of recent studies on the use of superplasticizers in modified (or combined form) to improve compatibility have shown promising outcomes to control the rheological properties of calcined clay binders. Superplasticizer demand required to achieve workable concrete increases with increasing dosage of calcined clay and increases substantially for concrete produced with calcined clay at water-to-cementitious material ratios below 0.40. A comparative analysis of data from several literature shows that the addition of calcined clay could reduce setting time when used without superplasticizers. Addition of superplasticizers could help to control and increase the setting time significantly. Calcined clay can be used to make concrete with similar workability and setting times as concrete containing Portland cement through the use of polycarboxylate-based superplasticizers. However, more studies in future should focus on retention of workability by suitable methodologies for various construction activities. Care should be exercised to avoid long setting times with high dosages of superplasticizers.

[EN] Approximately 140 billion metric tons of biomass are produced every year in the world from agriculture. The ashes resulting from firing agricultural wastes such as rice husk, sugar cane and others can be used as Supplementary Cementitious Materials (SCM). They can be mixed with lime alone or in ternary mixtures with Portland cement and lime. If fired at temperatures around 600-700 °C the agricultural ashes exhibit good reactivity. Despite extensive research work carried out on the use of agricultural ashes as source of SCMs, few success stories are reported on practical applications on an industrial scale. Details of the firing technology should be re-assessed, with special emphasis on the scale at which the technology begins to be economically suitable. Further research is also needed to understand the mechanisms of structural transformation of amorphous silica during calcination, and the impact of the ashes on cement hydration in blended systems.