Discovery Mat at Project ARCHIPAL Colloque final international -  Architecture, aluminium et patrimoine XXe-XXIe siècles. Entre innovation, patrimoine et environnement. Oral presentation: "Alloys and corrosion: what do the analyses say?" by Aurélia AZEMA, Christian DEGRIGNY, and Léopold REMY

October 23-24, 2023

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It was at the turn of the 20th century, when the new process for producing aluminium by electrolysis was invented, that this metal and its alloys were gradually used in construction. Initially, the material used was derived from other sectors of application (transport, energy, chemicals, packaging, etc.), but specific alloys with properties suited to construction (lightness, resistance to atmospheric corrosion, fire resistance, high reflectivity) were developed throughout the 20th century. Architects and construction engineers experimented with the new materials, using them to construct buildings with functions ranging from schools and office blocks to hospitals and public buildings (congress halls, exhibition buildings). As part of the Archipal project, a material study of a representative corpus of elements (façade panels, framework) from ten buildings using aluminium alloys was carried out. After assessing the condition of each element, it was necessary to adapt and test the contributions and limitations of available portable analysis techniques (X-ray fluorescence spectrometry - XRF, inductively coupled plasma atomic emission spectrometry - LIBS, electrochemical measurement - Discovery Mat) in order to build a relevant study methodology for the various elements (calibration, database). Where possible, in-depth laboratory analyses (X-ray diffraction - DRX on powder, optical and electron microscopy, the latter combined with energy dispersive spectroscopy - SEM / EDS, on stratigraphic sections, metallography, etc.) helped to clarify the nature of certain treatments applied to the alloys and to characterize their state of preservation. First of all, it became clear that the aluminium alloys chosen were suitable and appropriate for their purpose, right from the very first construction sites. This observation testifies to the mastery of materials by the engineers in charge of construction. It was also found that, at the scale of each building, the uses of aluminium alloys and their shaping techniques (casting, wrought) vary mainly between curtain wall panels and their frameworks, which are, in most cases, combined with other materials (metals, glass, wood, foam, etc.) in complex and ingenious assemblies. A variety of final treatments (anodizing, organic coatings, etc.) have also been observed to condition the visual appearance of the product, integrated into the architectural coherence of the construction. Finally, certain corrosion pathologies were characterized and linked to the nature of the alloy used and the environment in which it was exposed.

A brief summary of the Archipal project, objectives and achievements:

Over a period of 4 years, the ANR project "Architecture, aluminium and heritage in the 20th and 21st centuries" has been developing research into the history of aluminium in architecture, its heritage and its conservation.

Until now, the history of aluminium and its alloys in architecture had only been considered in a fragmented way, through monographic and biographical approaches, in which the figure of Jean Prouvé dominated. As the work progresses, the contributions of other players, such as Jean de Mailly and Marcel Lods, will help us to understand how this metal was approached, its qualities and the constraints it encountered. The cross-referencing of case studies by building or type of building also tends to show the differences in economic and technical issues from the point of view of the owners, architects, engineers and contractors.

This metal is a source of technical innovation and artistic creation, and incorporates societal issues such as sustainability and the circular economy. A better understanding of its spread over time and space, the strategies of those involved, and the techniques used for its installation and conservation, should help us to reflect on the objectives of sustainable development.

A corpus of old technical objects made of aluminium alloys has been compiled and studied throughout France to determine the nature of the alloys used over time, their state of conservation and the types of corrosion encountered. The creation of a multidisciplinary database will be made available in order to study the spread of its uses in the building industry and to help define conservation and restoration strategies.

This final symposium provided an opportunity to report on the work carried out and open up new avenues of research, particularly abroad.

The conference focused on three interdisciplinary themes: the history of aluminium alloys in architecture and the players involved, the process of heritage preservation and the state of conservation/restoration.”