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# The discovery of pozzolanic properties of calcined clays in the late 1700s in France and the technologies associated with its activation

Vincent Thiéry

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Vincent Thiéry. The discovery of pozzolanic properties of calcined clays in the late 1700s in France and the technologies associated with its activation. Applied Clay Science, 2025, 272, pp.107817. 10.1016/j.clay.2025.107817. hal-05035924

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https://imt-nord-europe.hal.science/hal-05035924v1

Submitted on 16 Apr 2025

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Short Communication

# The discovery of pozzolanic properties of calcined clays in the late 1700s in France and the technologies associated with its activation

Vincent Thiéry<sup>a,b,*</sup>

<sup>a</sup> IMT Nord Europe, Institut Mines-Télécom, Centre for Materials and Processes, F-59000 Lille, France

<sup>b</sup> Univ. Lille, Institut Mines-Télécom, LGCgE - Laboratoire de Génie Civil et géoEnvironnement, F-59000 Lille, France

## ARTICLE INFO

**Keywords:**

Calcined clays

Supplementary cementitious materials

Louis Vicat

History of science

## ABSTRACT

The current trend towards the use of calcined clays as supplementary cementitious materials might lead to the feeling that this technology is a recent development. However, the description of their pozzolanic properties, along with the ways to burn them correctly, dates back from the first half of the nineteenth century, within the industrial revolution– the preliminary idea was even published in 1787. In France, the famous chemist Louis Vicat made seminal descriptions of the type of clays involved and understood the chemistry behind the phenomenon. It gave rise to the use of the term “artificial pozzolan”.

## 1. Introduction

Limestone calcined clays cements (LC³) and to a broader extent the use of calcined clays as supplementary cementitious materials (SCM) are gaining an incredible interest within the global context of the quest for durability and the reduction of CO₂ emissions (Snellings et al., 2012, 2023; Scrivener et al., 2018). Indeed, calcined at much lower temperatures than Portland cement, in the 700–850 °C range, they need less energy to be produced and represent hence a promising alternative to traditional, clinker-based binders (Barbhuiya et al., 2023).

Despite the fact that most papers mention the use of artificial pozzolans such as calcined clays “for ages”, they often lack precision regarding the real timing of their discovery and there might be some misconceptions with the use of pozzolans dating back from the Roman times.

Hence, while the aforementioned LC³ represent a significant environmental and technical issue, it is worth of interest to go back to the roots of science in order to find out what pioneers had already done on the topic. Indeed, the period of the industrial revolution in France (and in Europe in general during the 19th century) was a time of intense intellectual, scientific and industrial prosperity. Many advances were done regarding all aspects of the society: building materials are part of those ones.

## 2. Historical recognition of artificial pozzolans

The discovery, in France, of natural (i.e. of volcanic origin) pozzolans, similar to the ones from Italy, by the famous volcanologist Barthélémy Faujas de Saint Fons (1741–1819) is well documented (Thiéry, 2024). Not only did this great scientist make thorough descriptions of lime/pozzolans mixtures and their hardening, he also paved the way towards the use of “artificial pozzolans” such as crushed bricks, tiles… as observed in Roman buildings.

The first documentation that pozzolans can be obtained artificially is due to the works of the famous chemist Jean-Antoine Chaptal (1756–1832, see biography in Wisniak, 2003). He published a specific treaty (Chaptal, 1787) about the possibility to obtain pozzolans from “ochreous earth” (Fig. 1). Indeed, contrarily to the aforementioned discovery of natural pozzolans in France, his interest was to produce artificial ones by mimicking the natural processes occurring in volcanoes: “At the surface of the globe, we often find earth which is similar to volcanic earth, and they only lack the effect of a volcanic fire to not be different at all. I have thought that the fire of our furnaces, more active than the one of volcanoes, since we vitrify easily what the volcano only sinters, could replace it advantageously”. This semantic, which is typical of French scientific literature from the end of the eighteenth century, seems a bit obscure and shows the lack of comprehension, at that time, of volcanism. However, the understanding that heat can have some effect on “earth” (here used in French in the sense of *soil* – *terre*), was already acquired.

<footnote>* Corresponding author at: IMT Nord Europe, Institut Mines-Télécom, Centre for Materials and Processes, F-59000 Lille, France.
E-mail address: vincent.thiéry@imt-nord-europe.fr.</footnote>
<figure><img src="image_4.png" /><figcaption>**Fig. 1.** The 1787 treatise by Chaptal dealing with the artificial way to obtain pozzolans: "observations on some advantages that can be obtained from ochreous earths, with the means to convert them in brown-red and to form pozzolans able to replace with savings both foreign and national ones". ©ar chive.org (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

### 3. The discovery of calcined clays as artificial pozzolans

Following the works of Chaptal, the famous chemist Louis Vicat (1786–1861, see biography in Boyer, 2020), widely known for the discovery of what would eventually become Portland cement, also got interest in pozzolans. He published a treatise in 1846 (Vicat, 1846, and Fig. 2), summarizing a lifelong work on binders, for which also several articles were published in various French journals. Indeed, as early as 1819 (his work about cement was published in 1818), he gave a lecture at the French national academy of science of a work entitled "research on artificial pozzolans", stating that "finely ground clays, calcined for five or six minutes on an iron plate heated to dark red, ultimately behave with lime as the best pozzolans from Italy". This lecture was published five years later (Vicat, 1824). It explains briefly that the pozzolanic activity, as it would be written now, of clays, can be enhanced by a rapid firing on a hot plate – the colour "dark red" must be seen as a way to describe the temperature, since no thermometer was available at that time (McCaskey, 2020). It also shows that Vicat had noticed that clays have to be ground – and not, for example, shaped in bricks – in order to promote their activation.

In 1842, his short communication "Upon the rate of heating necessary to the calcination of clays for the making of pozzolan" (Vicat, 1842a) contains the following fundamental observations: "this burning, to show the best efficiency, has to be limited to the total expulsion of water that constitutes the hydrated alumina silicate". He clearly insists on the limit of water expulsion, meaning that an excess of calcination might not be good for the pozzolan, which is now well known: mullite has to be avoided (Brindley and Nakahira, 1958; Claverie et al., 2015).

The same year, his short communication entitled "note on pozzolans" (Vicat, 1842b) also shows a deep understanding of the chemical phenomena occurring during the burning of clays. Indeed, he wrote that the "type pozzolan, I would almost say the theoretical pozzolan, is nothing else that an alumina silicate made almost anhydrous by a slight burning, and changed into the point where the affinity between silicon and alumina became as small as possible".

This statement is of uttermost importance regarding the initial understanding of the thermal activation of clays. Back in 1842, the atomic organization of those materials was unknown, and their X-ray crystallography began during the first quarter of the 20th century (Moore, 1987). Hence, their understanding was purely based on chemical considerations. In the aforementioned example, Vicat (1842b) mentions only silicon and alumina, meaning kaolinite $Al_2(Si_2O_5)(OH)_4$, turned anhydrous – what is nowadays called metakaolinite (or metakaolin). Moreover, he described the need to have the smallest possible affinity between silicon and alumina, this is nowadays known as amorphization (Shvarzman et al., 2003).

Other types of clays have also been investigated by those pioneers. However, the descriptions are really empirical, such as for example in the works of C.L. Treussart (1829), where he indicates all types of clay calcined correctly and powdered are prone to give artificial pozzolans, more or less efficient, depending on their composition. The better ones are fat clays, usually used to make earthenware. In any case, to come back to Vicat (1846), he gives the following details about clays: "Clays are mostly made of silicon, alumina and water; they form an almost infinite number of types [...] Gradually calcinated, all clays lose various parts of their bound water".

### 4. Pioneering the calcination of clays

Whereas the theoretical considerations and laboratory work, mainly of Louis Vicat, led him to understand and produce artificial pozzolans, it is worth mentioning that industrial devices were designed to achieve this purpose.

The French engineer Antoine Raucourt (1789–1841) published a Treatise on the art of making good mortars and to correctly use them (Raucourt, 1828). This thorough and detailed one deals with all aspects of mortars, from lime calcination and extinction, to pozzolans and mixing as well as mechanical testing. Widely illustrated, it presents a contraption to calcine clay (Fig. 3). Interestingly, the word used to describe the process is roasting. The description for its correct use states that clays must be calcined on a "cherry red" heated plate, divided.

### 5. Discussion and conclusion

Nowadays, calcined clays are obtained either using flash calcination (which lasts for a couple of seconds) or a traditional rotary kiln for ca. 30 min (Almenares et al., 2017; Hanein et al., 2021). As outlined by Henein et al. (2021), the process of firing clays for their use as SCM differs from the firing of clays to make bricks since they have to be thoroughly separated. Hence, for both points of view (the burning time and the process), it is interesting to notice that this was both understood and technically achieved almost 200 years ago (Fig. 3).

While those historical works are not strictly related to $LC^3$ since calcined clays were used in lime-based binders, it is in any case worth noting the technical and scientific knowledge acquired by famous early scientists, which are, in a certain way, only reproduced – and not invented – nowadays.

#### CRediT authorship contribution statement

**Vincent Thiery:** Writing – original draft, Investigation, Conceptualization.
<figure><img src="image_5.png" /><figcaption>Fig. 2. The 1846 treatise by L. Vicat, "new studies on artificial pozzolans compared with Italian pozzolan in their use in fresh water and sea water".</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 3. A 1828 device to calcinate clay (Raucourt, 1828). Historically, the term used was “roasting”. © Gallica.</figcaption></figure>

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

No data was used for the research described in the article.

References

Almenares, R.S., Vizcaíno, L.M., Damas, S., Mathieu, A., Alujas, A., Martirena, F., 2017. Industrial calcination of kaolinitic clays to make reactive pozzolans. Case Stud. Construct. Mater. 6, 225-232. https://doi.org/10.1016/j.cscm.2017.03.005.

Barbhuiya, S., Nepal, J., Das, B.B., 2023. Properties, compatibility, environmental benefits and future directions of limestone calcined clay cement (LC3) concrete: a review. J. Build. Eng. 79, 107794. https://doi.org/10.1016/j.jobe.2023.107794.

Boyer, P.-O., 2020. Eminent Structural Engineer: Louis Vicat. Struct. Eng. Int. 30, 128-130. https://doi.org/10.1080/10168664.2019.1693248.

Brindley, G.W., Nakahira, M., 1958. A new concept of the transformation sequence of kaolinite to mullite. Nature 181, 1333-1334. https://doi.org/10.1038/1811333a0.

Claverie, M., Martin, F., Tardy, J.P., Cyr, M., De Parseval, P., Grauby, O., Le Roux, C., 2015. Structural and chemical changes in kaolinite caused by flash calcination: formation of spherical particles. Appl. Clay Sci. 114, 247-255. https://doi.org/10.1016/j.clay.2015.05.031.

Hanein, T., Thienel, K.-C., Zunino, F., Marsh, A.T.M., Maier, M., Wang, B., Canut, M., Juenger, M.C.G., Ben Haha, M., Avet, F., Parashar, A., Al-Jaberi, L.A., Almenares-Reyes, R.S., Alujas-Diaz, A., Scrivener, K.L., Bernal, S.A., Provis, J.L., Sui, T., Bishnoi, S., Martirena-Hernández, F., 2021. Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL. Mater. Struct. 55, 3. https://doi.org/10.1617/s11527-021-01807-6.

McCaskey, J.P., 2020. History of 'temperature': maturation of a measurement concept. Ann. Sci. 77, 399-444. https://doi.org/10.1080/00033790.2020.1817980.

Moore, D.M., 1987. Roentgen, von Laue, the Braggs, X-Ray diffraction, and the development of clay mineralogy. J. Geol. Educ. 35, 28-32. https://doi.org/10.5408/0022-1368-35.1.28.

Raucourt, A., 1828. Traité sur l'art de faire de bons mortiers et d'en bien diriger l'emploi, ou Méthode générale pratique pour fabriquer en tous pays la chaux, les ciments et les mortiers (Malher. ed).

Scrivener, K., Martirena, F., Bishnoi, S., Maity, S., 2018. Calcined clay limestone cements (LC3). Cem. Concr. Res. 114, 49-56. https://doi.org/10.1016/j.cemconres.2017.08.017.

Shvarzman, A., Kovler, K., Grader, G.S., Shter, G.E., 2003. The effect of dehydroxylation/ amorphization degree on pozzolanic activity of kaolinite. Cem. Concr. Res. 33, 405-416. https://doi.org/10.1016/S0008-8846(02)00975-4.

Snellings, R., Mertens, G., Elsen, J., 2012. Supplementary cementitious materials. Rev. Mineral. Geochem. 74, 211-278. https://doi.org/10.2138/rmg.2012.74.6.

Snellings, R., Suraneni, P., Skibsted, J., 2023. Future and emerging supplementary cementitious materials. Cem. Concr. Res. 171, 107199. https://doi.org/10.1016/j.cemconres.2023.107199.

Thiéry, V., 2024. Barthélémy Faujas de Saint-Fond (1741-1819) and his work on pozzolans and lime: a pioneer in sustainable building. Proc. Geol. Assoc. 135, 481-485. https://doi.org/10.1016/j.pgeola.2024.04.004.

Treussart, C.L., 1829. Mémoire sur les mortiers hydrauliques et sur les mortiers ordinaires.

Vicat, J., 1824. Recherches sur les Pouzzolanes artificielles. Mémoires de l'académie royale des sciences de l'institut de France, années 1819 et 1820, pp. 53-54.

Vicat, L., 1842a. Sur le degré de chaleur nécessaire à la calcination des argiles pour la fabrication de la pouzzolane. Compt. Rend. Hebdomad. l'Acad. Sci. 14, 274.

Vicat, L., 1842b. Note sur les pouzzolanes. Compt. Rend. Hebdomad. l'Acad. Sci. 14, 955-957.

Vicat, L., 1846. Nouvelles études sur les pouzzolanes artificielles comparées à la pouzzolane d'Italie dans leur emploi en eau douce et en eau de mer.

Wisniak, J., 2003. Jean Antoine Chaptal. Rev. CENIC. Cienc. Químic. 34, 159-165.