An unfinished Pompeian construction site reveals ancient Roman building technology
Nature CommunicationsTL;DR
Imagine you're baking a cake. Modern concrete is like using a standard, room-temperature cake mix. This research found that the Romans used a different recipe: they mixed a very reactive ingredient called 'quicklime' with dry volcanic ash *before* adding water. This is like adding a bath bomb to your dry ingredients – when they finally added water, the whole mix got very hot. This 'hot mix' created special, little white chunks in the finished concrete. For centuries, people thought these chunks were mistakes. It turns out, they're the secret sauce: if a tiny crack forms and water gets in, these chunks dissolve and create a natural cement that automatically fills the crack. The concrete literally heals itself.
Recent excavations at Pompeii’s Regio IX have uncovered an intact ancient construction site, offering insights into Roman building techniques at the time of the eruption of Mount Vesuvius in 79 CE. Microstructural and chemical analysis of materials collected from previously constructed walls, walls under construction, and adjacent dry, raw material piles show unequivocally how quicklime was pre-mixed with dry pozzolan before adding water in the creation of Roman concrete. This construction method, also known as hot mixing, results in an exothermic reaction within the mortar and the formation of lime clasts, key contributors to the self-healing and post-pozzolanic reactivity of hydraulic mortars. The analysis of reaction rims around volcanic aggregates demonstrate aggregate/matrix interfacial remodeling, where calcium ions originating from the dissolution of lime clasts diffuse and remineralize, producing amorphous phases and various polymorphs of calcium carbonate (including calcite and aragonite). Furthermore, the parallel discovery of masonry materials and tools permits elucidation of the entire construction workflow, including the steps required to process binding mortars and larger aggregates (caementa). These findings advance our understanding of ancient Roman construction and long-term material evolution, providing a scientific basis for developing more durable and sustainable concretes and restoration materials inspired by ancient practices. Here the authors combine microstructural and chemical analysis of building materials collected from an active construction site in Pompeii prior to the eruption of Mount Vesuvius in 79 CE. Through these analyses, they identify the key raw materials and processes used in the production of Roman concrete.
- 1Uncovered an ancient construction site at Pompeii, offering insights into Roman techniques when Mount Vesuvius erupted.
- 2Identified how quicklime was pre-mixed with dry pozzolan before adding water to create Roman concrete.
- 3Discovered an exothermic reaction in the mortar leading to the formation of lime clasts.
- 4Identified the entire construction workflow, providing a basis for modern sustainable construction materials.
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