This book is part of a series titled Treatise on Concrete, which is edited by Roberto Gargiani and published by his university, the École Polytechnique Fédérale de Lausanne. Concrete from Archeology to Invention 1700–1769, authored by Gargiani, is the first of a group of works within the series that focus on the development of concrete during the eighteenth and nineteenth centuries in Europe. In the preface, Gargiani states that the book's goal is to document the evolution of construction techniques through archival research. Indeed, he presents a tremendous amount of material from treatises, old journals, personal letters, and state entities that are otherwise not easily accessible. In fact, large portions of the text consist of quotations (translated into English) from the archival sources. On the one hand, this is a useful service, but on the other, any sort of narrative is lost in the minutiae. The author's interest in the people who wrote the documents is reflected in his choice to index only proper names and not places or subjects. Nevertheless, the volume contains a wealth of valuable information if one is willing to mine for it.
The book begins with an exploration of the period when researchers were trying to discover the secret of the longevity of Roman concrete. Vitruvius's treatise offered a starting point, with its formulas for creating hydraulic mortar with pulvis (powder) from the Bay of Naples (Pliny the Elder's pulvis Puteolanus, powder from Puteoli—i.e., volcanic ash), but many people at the time believed that ancient craftsmen long before Vitruvius had created a type of mysterious artificial stone, pierre fondue (11–14). Gargiani notes that developments during the eighteenth century were marked by “an extraordinary mixture of scientific research and fantastic interpretation of sources and ruins” (11). One might even see these competing approaches as a reflection of the contemporary conflict between faith and reason that was permeating European society.
An example of the mystical approach is that of Richard Holt, who firmly believed that both Egyptians and the builders of Stonehenge had invented artificial stones.1 In 1722, he began to file patents for methods of creating artificial stone, which he called his “secret composition.” Gargiani reports from Holt's treatise that the secret method involved a blast furnace, clays, glass, ores, and vitrified stone, which were used to create a substance that was poured into molds (225–30). Gargiani devotes five pages to this mysterious product, yet the reader is ultimately left with no explanation as to what it actually was. This is an early example in the book where a critical evaluation (and rational explanation) of the substance under discussion would have been valuable as a means of elucidating the understanding of material properties at that time.
In the second chapter, the author presents information on the various ingredients found in Europe and imported from afar that were used to produce hydraulic mortar, but he provides no explanation of the basic chemistry involved. Today we know that hydraulic lime mortar is created when slaked lime (calcium hydroxide) is combined with an additive containing soluble silica that reacts to form calcium silicate hydrate (C-S-H). A variety of materials can be used as additives (e.g., volcanic ash, terracotta, siliceous earths). Ironically, the chapter contains a section headed “Chemistry Research on Lime” (144–59), but it does not include this fundamental information. Another problem is that there is no coherent discussion of the terminology used, such as cement, mortar, and concrete. This is a complicated issue, because similar words have different meanings in different languages. The difficulty of translating cognates between languages is exacerbated by the fact that Gargiani wrote the book in Italian, many of his resources are in French, and someone else translated the manuscript into English. The unfortunate result is that the terms above are simply used interchangeably throughout the text.
These problems aside, the second chapter sets up the context of the pozzolana (volcanic ash) trade in western Europe during the eighteenth century. The two major sources were pozzolana from central Italy and trass from Germany. Central Italy had two main products: red pozzolana from Rome, which was shipped from the port at Civitavecchia (under papal control), and gray pozzolana (pulvis Puteolanus), which was shipped from the Bay of Naples (under control of the Kingdom of Naples). In spite of the superiority of the Naples product, the pozzolana from Rome was the dominant Italian export and a major source of income for the Papal State (338). Trade was very much affected by politics. For example, the English navy was involved in trying to prevent the French, the largest importer, from acquiring the pozzolana needed for their building works. Gargiani traces some of the intricate deceptions undertaken by the French in their efforts to acquire what they needed (55–58). The second source, the German trass, a consolidated volcanic ash (tuff), was mined along the Rhine. Much of this stone was sent downriver to Holland, where windmill power was used to grind the stones to a powder that could be used to make hydraulic mortar. The Dutch then exported this powder to England, France, and Denmark, and even back to Germany. It is not surprising that some of the major researchers looking for alternative methods of making hydraulic mortar lived in countries like France (Jean-Étienne Guettard, Jacques-Germain Soufflot), England (John Smeaton), and Sweden (Axel Fredrik Cronstedt), which had to import the Italian and Dutch materials.
Throughout the rest of the book, Gargiani examines methods of using hydraulic mortar, with particular attention to the shift from using cofferdams (wooden structures built on riverbeds or seabeds and pumped dry) to caissons (floating wooden boxes that are sunk into place). He traces the developments through numerous case studies in Italy, France, Spain, and England. The one that reappears throughout the book is the project at Venice to protect the lagoon with levees (81–100, 186–205, 251–56). The techniques used before the eighteenth century involved wooden pilings and rocks, but with the invasion of the “shipworms” (teredinidae), which destroyed the wood, the Venetians began searching for new methods. Following experiments with earlier prototypes (81–100), in 1735 Bernardo Zendrini advocated for caissons filled with hydraulic mortar (188), but first he had to find a mortar that would harden underwater. After trying local materials (“Vincenza pozzolana” and “Padua lime”), he realized that higher-quality pozzolana from Rome or Naples was required (191–92). Given the success of the project, the Venetian Republic set up administrative procedures to acquire the vast amount of pozzolana needed, most of which came from Civitavecchia (200–204). The exportation of Roman pozzolana increased so much during this period (1740–70) that the pozzolana quarry tunnels beneath Rome itself began to cause building collapses (51).
In 1756, John Smeaton was making his own mortar experiments with his friend William Cookworthy, a chemist, in preparation for rebuilding the Eddystone Lighthouse on the English Channel. They devised a method of testing various mortar recipes by employing different varieties of lime together with different types of pozzolanic additives, including trass and pozzolana from Rome. The latter was a product rarely shipped to England, but by chance a merchant had purchased a load of pozzolana to sell in London (54–55, 309–17), and when his venture was unsuccessful, he sold it to Smeaton at the same price as the trass. Ultimately, Smeaton discovered that the Roman pozzolana and hydraulic lime from the local blue Lias limestone created the most effective hydraulic mortar. The lighthouse, completed in 1759, was the first major structure in England built with pozzolana mortar.
At the same time, Giovanni Battista Piranesi published Le antichità romane (1756), in which he first began to document Roman construction details. As Gargiani notes, “It is only with Piranesi that the veduta genre converges with the tradition of technical drafting of architects,” and this led to an even broader interest in ancient Roman construction techniques (258). The author also points out that Piranesi had worked in the office of the Magistrato alle Acque at Venice, headed by his uncle, where he gained direct knowledge of Zendrini's work on the lagoon project, and proposes that many of Piranesi's vedute in Le antichità romane were “secret commemorations” of what he had learned about concrete in Venice.
These are samplings of the narratives that I was able to tease from the text. I learned much, but the reading was difficult. Overall, the book lacks coherent organization and consists of impenetrable prose awkwardly translated from the Italian. Even more frustrating is the lack of critical commentary on the archival material, which is simply presented at face value, often leaving the reader with the impression that the opinions quoted, especially regarding chemistry and archaeology, are true in cases where we now know them to be wrong. The book is heavily illustrated with nicely reproduced color images of the archival drawings, but unfortunately the images are not referenced in the text. This volume provides a valuable resource, especially for those who already know the subject and the period and who are looking for documentary evidence, but readers of all types will find that extracting the information is a challenging endeavor.