In half a century, concrete, a symbol of modernity and architectural durability, has lost much of its appeal. Sensitive to erosion, often synonymous with impersonal urbanization, it is criticized for its ecological impact. Recent discoveries on Roman concrete could, however, renew our interest in it.
The term concrete refers to various composite materials whose common point is to mix inert matter, gravel or sand for example, with a binder which can be clay, bitumen or even cement. The result is a kind of artificial stone that takes shape in a workshop or can be cast directly in a building site.
Thus rammed earth and cob are ancient forms of concrete. The Egyptians already used a mixture of lime, clay, sand and water and made mortar – a name given to concrete whose mineral part is entirely composed of sand. A now abandoned hypothesis, developed from the end of the 1970s, even suggested that the pyramids had been built from concrete blocks made on site. Going further back in history, we find mixtures based on clay in Mesopotamia, a fragile association of which we have kept few traces.
The Romans, inventors of modern concrete
Concrete in the modern sense of the term appeared with the Romans and has fascinated people ever since for its incredible longevity. It was used, for example, for the construction of the largest unreinforced concrete dome, without metal reinforcement, that of the Roman Pantheon. Weighing more than 5,000 tons, with a diameter exceeding 43 meters, it will celebrate its 1900th anniversary next year, without revealing any notable fragility, having withstood the outrages of men and seismic tremors.
It was long believed that this extraordinary solidity came from the use of pozzolan – a rock from volcanic scoria, notably Vesuvius. A study conducted by the Massachusetts Institute of Technology (MIT) whose results were published in early 2023, showed that the formidable self-repairing capacities of Roman concrete were due to the use of quicklime brought to a very high temperature.
When a crack appears, the concrete produces in contact with water a solution saturated with calcium which, by changing into calcium carbonate, immediately fills the void. Thus, even the seaside structures built by the Romans have withstood the ravages of time.
When concrete fascinated architects
It was not until the end of the 18th century that natural cement reappeared, particularly in the south-east of France. At the beginning of the following century, Louis Vicat invented artificial cement, based on the firing of a fair proportion of limestone and clay. Then a patent was developed in England protecting the so-called Portland cement. The use of artificial stones is developing and concrete is also used in decoration in Italy, instead of stucco, notably in what remains the largest covered passageway ever built, the Victor-Emmanuel II Gallery in Milan.
Towards the end of the 19th century, we tried our hand at reinforced mortar reinforcements with the Saint-Jean de Montmartre church, for example. The appearance is still that of brick and the manufacturing cost remains high. In 1898, rue Danton in Paris, appeared the first apartment building in reinforced concrete. These two techniques go hand in hand with developments in iron architecture which, from the Grand Palais to the Eiffel Tower, are the delights of Universal Exhibitions.
Concrete fascinates avant-garde architects, not without a few colorful episodes. Thus, the owners of the Savoye villa in Poissy bear the brunt of experiments in Le Corbusier on the flat roofs: it is raining in the entrance, along the garage and even in the bathroom.
Are we heading towards the end of concrete?
Military needs bring concrete into the air of mass architecture, with the Maginot Line wanted to protect France from the German invasion, then the Atlantic Wall supposed to warn the Germans of any Allied landings. The post-war period made it the king material for reconstruction, with sometimes, as in Le Havre by Auguste Perretreal urban feats.
The era of large housing estates and major road infrastructure developments takes away some of its luster, but makes it the most conspicuous sign of modernity. Of The Pier of Chris Marker To Hatred by Mathieu Kassovitzconcrete dresses both the France of the “Glorious Thirties” and that of the crisis in the suburbs.
” Todayexplains Cyrille Hanappe, architect-engineer and lecturer at ENSA Paris-Belleville, concrete has gone out of fashion, but it continues to be poured by hectolitres. It’s a bit like the gasoline car, before we stop, it’s going to be some time. This obviously calls into question this impression of durability, which experience has shown us hardly goes beyond half a century. After this time, you have to choose between destruction and rehabilitation, which raises the question of the cost, but also that of the carbon impact, which can no longer be ignored.
” Concrete is much more compatible with capitalism than earthcontinues Cyrille Hanappe, it is fluid, it flows, we transport it. A whole industry is thus developing around him. It is also in this sense, he concludes, that ” Roman concrete really raises questions “. And since their discovery, the MIT researchers have not forgotten the question of profit. They are already thinking about marketing it.
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