The following study focuses on achieving harmonization of cement standards at the international level, with a trend towards the use of sustainable materials that increasingly lead to a Net Zero society. Several cements with different clinker additions were analyzed in order to evaluate their performance by compressive strength as well as the influence of fineness and workability parameters might have on them, following the procedures established in the international standards ASTM and CEN. It was evident that LC₃ cement, despite the differences found in the testing procedures, maintained always excellent quality. This study allows us to assess whether the methodological differences identified between both standards influence the physical-mechanical parameters of the cement and promotes the need for the application of this cement in international projects.

LC3 (limestone calcined clay cement) is poised to become the construction industry’s future as a so-called low-carbon-footprint cement. Research into this subject has determined the minimum kaolinite content in calcined clays to guarantee good mechanical performance. This study examines the use of clay from the Valencian Community (Spain), which has a lower kaolinite content than the recommended amount (around 30%) for use in LC3 and how its performance can be enhanced by replacing part of that clay with metakaolin. This study begins with a physico-chemical characterisation of the starting materials. This is followed by a microstructural analysis of cement pastes, which includes isothermal calorimetry, thermogravimetry, and X-ray diffraction tests at different curing ages. Finally, this study analyses the mechanical performance of standard mortars under compression to observe the evolution of the control mortars and the mortars with calcined clay and metakaolin over time. The results show that the LC3 mortars exhibited higher compressive strength in the mixtures with higher calcined kaolinite contents, achieved by adding metakaolin. Adding 6% metakaolin increased the compressive strength after 90 days, while 10% additions surpassed the control mortar’s compressive strength after 28 days. Mortars with 15% metakaolin exceeded the control mortar’s compressive strength after just 7 curing days. The hydration kinetics showed an acceleration of LC3 hydration with metakaolin additions due to the nucleation effect and the formation of monocarboaluminate and hemicarboaluminate (both AFm phases). The results suggest the potential for combining less reactive materials blended with highly reactive materials.

With over 8% of global carbon emissions worldwide, the cement industry is challenged to lower its carbon footprint. Replacement of clinker in cementitious systems becomes crucial. Sound research proved that kaolinitic clays with as low as 40% kaolinite can have a high reactivity as SCM. Further research studies found a synergy between the aluminates in calcined clays and the carbonates in limestone that led to the proposal of a ternary binder called Limestone Calcined Clay Cement, LC3, consisting of 50% Portland Cement, 30% calcined clay and 15% limestone. This paper presents the efforts of a group of members from 41 universities and 17 industrial partners through the RILEM Technical Committee 282 – CCL: Calcined Clays as Supplementary Cementitious Materials. The work was oriented to fill existing information gaps on characteristics of clay minerals, the process of clay calcination, hydration of cementitious systems containing calcined clay and limestone, fresh and hardened properties of concrete, standardization, and durability of concrete produced with binders containing calcined clay and limestone. The TC 282-CCL has published 10 whitepapers, with a strong contribution to a better knowledge and understanding of the role of calcined clay in cement and concrete.

For natural materials so heterogeneous from the mineralogical point of view as kaolinitic clays, it is important to understand the effect that mineralogical composition may have on its pozzolanic reactivity once calcined. In this paper, the pozzolanic reactivity of the calcination products at different temperatures of five kaolinitic clays is analyzed. Two kaolinitic clays were collected from clay deposits associated to weathering crusts, while the other three are associated to hydrothermal alteration phenomena. Analysis by XRD, TGA, and XRF of the kaolinitic clays indicates a kaolinite content ranging from 10 to 72 wt.

Overcalcined clays could be available as industrial by-products of the ceramic or refractory industries or may be produced as a result of an uncontrolled clay calcination process. Therefore, it is important to understand the effect of overcalcination on the behavior of calcined clays as pozzolans. In this paper, the pozzolanic reactivity of a kaolinitic clay with a high kaolinite content and calcined at temperatures from 800 to 1000 ºC is investigated. Analysis by XRD and XRF indicates a 72

This study aims at the evaluation of different formulations of concrete made with calcined clays and limestone (LC3 cement) exposed to aggressive environments. The study includes the evaluation of fresh and hardened properties and a comprehensive evaluation of durability over 24 months. The inclusion of calcined clays in cement increases the specific surface area of the cements, and thus the water demand. However, the high reactivity of calcined clays compared to any other pozzolan, and the synergy that occurs with limestones, enables the use of cements with very low clinker content that achieve strengths similar to those of Portland. Comparisons of LC3 formulations with Portland cement and with concrete containing silica fume prove the superiority of calcined clays in terms of strength and durability. The best results are obtained with LC3-50 cement with 50% clinker produced through co-grinding. Results of concrete made with a blend of 70% Portland cement with 30% LC2 (60% calcined clay, 35% limestone, 5% gypsum, separate ground) are also promising. All concretes made with LC3 show good durability in terms of the results of effective porosity, chloride permeability, and resistivity tests.

Calcined kaolinitic clays are known to be very reactive pozzolans, and combined with limestone can enable significant clinker substitution in cementitious systems. Thermal activation of kaolinitic clays takes place when the hydroxyl groups are removed, leading to formation of an amorphous reactive structure. There are several technologies for clay activation, but the most used at industrial scale are flash and stationary calcination. The objective of this paper is to investigate the impact of the calcination regime on the properties of the calcined product. It presents the results of an experimental program carried out with a kaolinitic clay calcined at a flash calciner and at a laboratory furnace. Calcination brings about a drop in specific surface, and an increase of average diameter due to agglomeration, an effect more pronounced in stationary calcination. No major differences were found at the heat of hydration, CH consumption and phase assemblage for the fully dehydroxylated material. The flash calcined material had slightly better results mainly due to a finer PSD compared with the one stationary calcined. No major difference was found in water demand and compressive strength for both regimes. As expected, the main impact of the calcination regime is the agglomeration.

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.

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-purity calcined clay-based concrete for reducing carbon footprint and improving durability performance in chloride exposure.

Together with the additives, the use of Supplementary Cementitious Materials (SMCs) is one of the most sustainable solutions worked on to achieve high performance concretes, more resistant to aggressive environments and as a measure to mitigate different phenomena, such as shrinkage cracks. Mineral additions are one of the most widespread, as they not only favour the partial replacement of Portland cement, but also provide certain chemical and physical properties that make the concrete more durable in different environments. The development of technologies that allow these new materials to appear requires studies to determine their influence on construction. This is why this research is focus on evaluating the effect of the active mineral addition of calcined clay, limestone and gypsum (LC2), on the shrinkage that occurs in fluid concretes and their behaviour in the paste-concrete ratio. Samples P35 (Cement P-35 and Sika Plast additive 0.65%) and LC65 (Cement P-35, addition LC2 30% and Sika Plast additive 1%) are defined. They are evaluate by means of chemical shrinkage in cement pastes and then a study is made of the shrinkage in the concretes by means of ASTM c-157 and the shrinkage channel. This research demonstrates the shrinkage reducing effect of the mineral addition LC2 and achieves an important step forward in the sustainable development of new materials for the Construction Industry in Cuba.

The acceleration of the impact of climate change prompts the cement industry for swift and effective solutions to reduce a large part of the carbon dioxide associated with cement manufacture. The use of Supplementary Cementitious Materials, SCM, such as fly ash and slag have enabled so far, the possibility of partially replacing clinker, the most energy intensive and main responsible component in cement for carbon emissions. However, reserves of both SCM are declining and their price is increasing, and replacing more than 30% clinker with these SCM can compromise early strength. In recent years a global team of scientists from Switzerland, Cuba and India have proven the possibility of dropping clinker content in cement down to 50% or even less through the combined use of calcined kaolinitic clays and limestone, both cheap and abundant materials, to produce a new cement called “LC3”. The resulting cement matches the properties of a CEM I (EN‐197) at all ages, and carbon emission reduction is reportedly around 25‐40%, depending on the cement to compare with. This paper presents the accumulated experience in the investigation of the new cementitious system and the introduction at the industrial level. Issues like the choice of the right clay, calcination technology, product formulation, standardization and economic feasibility will be discussed. The information in this paper is intended to encourage industrial partners to invest in the new technology.

The inclusion of high specific surface materials such as calcined clays in cementitious systems enhances the hydration of clinker products at very early ages, but it may also increase water demand; thus, the pursuit of a flowing concrete may demand an increase in the dosage of superplasticizers. The grinding regime can have a major influence on the properties of the cementitious system and could help mitigate the problem of water demand. This paper discusses the impact of grinding alternatives for the production of a binder consisting of clinker, calcined clay, limestone and gypsum. Two main target products will be discussed: (i) LC3, a binder with a formulation of 50% clinker, 30% calcined clay, 15% limestone and 5% gypsum, co-ground all together, and (ii) LC2, a mineral addition with a formulation of 60% calcined clay, 35% limestone and 5% gypsum, ground separately and further blended with Portland cement on a 1:1 basis (mass). The experimental program is carried out in several stages: (i) the binder, (ii) cement pastes and (iii) standard mortars, and concrete grinding aids from the family TEA are used to enhance grinding, and their impact is also be assessed.

The durability performance of blended cementitious systems with calcined clays is reviewed in this paper by the RILEM TC 282-CCL on calcined clays as supplementary cementititous materials (SCMs) (working group on durability). The impact of metakaolin and other calcined clays on the porosity and pore structure of cementitious systems is discussed, followed by its impact on transport properties such as moisture ingress. The durability performance of binary and ternary cementitious systems with calcined clay is then reported with respect to chloride ingress, carbonation, sulphate attack, freeze–thaw and alkali-silica reaction. The role of unique microstructural alterations in concretes with calcined clay-limestone combinations due to the formation of CO3-AFm and their impact on different durability exposures is emphasised. While a large majority of studies agree that the chloride resistance of concretes with calcined clays is significantly improved, such concretes seem to be more susceptible to carbonation than those produced with plain Portland cement or other SCMs used at lower replacement levels. Also, several studies are focused on metakaolin and lower grade kaolinite clay, while there are limited studies on calcined smectite/illite or mixed clays, which could also play a crucial role to the improved adoption of large reserves of clay sources to produce sustainable binders.

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.

Introducción: La implementación a escala industrial de la producción de los cementos LC3 y de la correspondiente adición mineral activa (LC2) se encuentra limitada porque no existe una adecuada estrategia que permita la identificación y evaluación de los depósitos arcillosos existentes como fuente de materiales cementicios suplementarios (MCS) y a sus limitados recursos reportados. El presente trabajo tiene como objetivo el desarrollo de un procedimiento que permite la identificación y evaluación de depósitos arcillosos para ser empleados como MCS y establecer los parámetros para su adecuada selección. Métodos: Se estudiaron cuatro depósitos arcillosos, los cuales se caracterizaron química y mineralógicamente. Las arcillas investigadas se calcinaron a 750 y 850 ºC, y fueron evaluados en su estado anhidro, en pastas y en morteros. Resultados: En las arcillas caracterizadas existe un predominio de los minerales arcillosos del grupo de la caolinita, mientras que sus relativamente altos contenidos de hierro limitan su explotación en aplicaciones propias de los caolines industriales. Los productos calcinados muestran una excelente reactividad puzolánica y los aglomerantes presentan un comportamiento similar a los cementos P-35. Conclusiones: Los cuatro depósitos presentan potencialidades para la producción de MCS a escala industrial. El contenido de caolinita, es el factor de mayor influencia sobre la reactividad puzolánica. La presencia de minerales acompañantes térmicamente inestables durante el proceso de calcinación también afecta la reactividad puzolánica. El procedimiento desarrollado constituye una sólida herramienta para la evaluación de las potencialidades de los depósitos arcillosos como fuente de MCS.

The use of supplementary cementitious materials (SCMs) to replace part of the clinker in cement is the most successful strategy to reduce CO2 emissions in the global cement industry. However, limited supplies of conventional SCMs make it difficult to take this strategy further unless new types of SCMs become available. The only type of material available in the quantities needed to meet demand is clay containing kaolinite, which can be calcined to produce an effective SCM. Such clays are widely available in countries where most growth in demand for cement is forecast. Calcined clays have previously been used as pozzolans, but calcination makes the economics of substitution marginal in a conventional pozzolanic blend. The major innovation presented here is the possibility to make a coupled substitution of cement with calcined clay and limestone. This allows much higher levels of substitution. Blends where calcined clay is used as a pozzolan, typically have clinker contents around 65–70%. Combination of calcined clay with limestone allows higher levels of substitution down to clinker contents of around 50% with similar mechanical properties and improvement in some aspects of durability. The replacement of clinker with limestone in these blends lowers both the cost and the environmental impact.

Introduction: The industrial scale implementation of the production of LC3 cements and the corresponding active mineral addition (LC2) is limited because there is no adequate strategy that allows for the identification and evaluation of the existing clay deposits as a source of supplementary cementitious materials (MCS) and its scarce reported resources. The goal of this work is to develop a procedure that allows for the identification and evaluation of clay deposits to be used as MCS and to establish the parameters for their suitable selection. Methods: Four clay deposits were studied, which were chemically and mineralogically characterized. The clays investigated were calcined at 750 and 850 oC and were characterized from the chemical point of view and the specific surface, and their pozzolanic reactivity was assessed. The calcined clays were used in the formulation of LC3 cements, which were evaluated in their anhydrous state, in pastes and in mortars. Results: In the characterized clays there is a predominance of clay minerals from the kaolinite group, while their relatively high iron content limits their exploitation in applications of industrial kaolins. The calcined products show an excellent pozzolanic reactivity and the binders show a similar behavior to the P-35 cements. Conclusions: The four deposits present potentialities for the production of MCS on an industrial scale. Kaolinite content is the factor with the greatest influence on pozzolanic reactivity. The presence of thermally unstable accompanying minerals during the calcination process also affects pozzolanic reactivity. The procedure developed constitutes a solid tool for evaluating the potentialities of clay deposits as a source of MCS.

This article reviews the rapidly developing state-of-the-art literature available on the subject of the recently developed limestone calcined clay cement (LC3). An introduction to the background leading to the development of LC3 is first discussed. The chemistry of LC3 hydration and its production are detailed. The influence of the properties of the raw materials and production conditions are discussed. The mixture design of concrete using LC3 and the mechanical and durability properties of LC3 cement and concrete are then compared with other cements. At the end the economic and environmental aspects of the production and use of LC3 are discussed. The paper ends with suggestions on subjects on which further research is required.

The combined use of calcined clays and limestone in the ternary system LC3 enables up to 50% of clinker substitution without affecting the performance. Low grade calcined clays are rich in iron. If calcined in an oxygen rich atmosphere, they turn to red. Cement producers avoid selling cement with a color different to the traditional. This paper proposes a method to modify color during calcination by controlling the atmosphere during the cooling. At calcination, the high temperature favors the formation of magnetite even at oxidizing conditions. However, during the cooling phase, magnetite can convert back to hematite if oxygen is available and the calcined material will have a reddish color. The procedure to control color consists of injecting liquid fuel at the carcass of the kiln while the calcined material exits, so that it combusts and exhausts the oxygen available during the cooling process. The procedure was successfully implemented at a pilot kiln in India. Controlling the calcination atmosphere enabled the production of a black calcined clay, instead of a red material. The reactivity and properties of both red and black clay are very similar, and no side effects have impacted properties of LC3 cements produced with the treated clay.