Romans mixed concrete that lasted better than many modern-day batches

The majestic structures of ancient Rome have survived for millennia — a testament to the ingenuity of Roman engineers, who perfected the use of concrete.

But how did their construction materials help keep colossal buildings like the Pantheon (which has the world’s largest unreinforced dome) and the Colosseum standing for more than 2,000 years?

Roman concrete, in many cases, has proven to be longer-lasting than its modern equivalent, which can deteriorate within decades. Now, scientists behind a new study say they have uncovered the mystery ingredient that allowed the Romans to make their construction material so durable and build elaborate structures in challenging places such as docks, sewers and earthquake zones.

The study team, including researchers from the United States, Italy and Switzerland, analyzed 2,000-year-old concrete samples that were taken from a city wall at the archaeological site of Privernum, in central Italy, and are similar in composition to other concrete found throughout the Roman Empire.

They found that white chunks in the concrete, referred to as lime clasts, gave the concrete the ability to heal cracks that formed over time. The white chunks previously had been overlooked as evidence of sloppy mixing or poor-quality raw material.

That doesn’t mean that “old” is always better than new. Just that it can be. 🙂

2 thoughts on “Romans mixed concrete that lasted better than many modern-day batches

  1. Pedant says:

    Across the top of the pantheon it says “MAGRIPPALFCOSTERTIVMFECIT” which translates to:
    “M(arcus) Agrippa, son (F) of Lucius (L), Consul (COS) for the third time (Tertium), built this.” Apparently this is misleading, as Agrippa did not build this Pantheon. Agrippa built the first Pantheon in 25BC which was destroyed by a fire in 80AD. The current Pantheon was built by Emperor Hadrian who honored Agrippa by inscribing what was written on the first Pantheon.

  2. p/s says:

    “…Despite extensive literature related to the composition and applications of ancient Roman concretes, the exact order of operations for Roman mortar production based on historical evidence remains ambiguous. There is even debate as to whether preparation techniques differed between the production of marine and terrestrial cementitious structures (12). Imperial age mortar (according to Vitruvius) was prepared by mixing lime with volcanic sand (materies ex calce et harena mixta). During the Republican period, Cato, in his De Agri Cultura (50), describes the mortar mix as calx harenatus (“lime with sand”). The wet mortar mix would then be mixed with tuff and brick caementa to form a concrete. In general, for frescoes and wall plaster, for example, the ancient scholars would often suggest the aging of lime in water before use and ensure that it was as finely ground as possible (17), because incompletely hydrated lime particles, known as bottaccioli in these applications, could absorb water over time and expand, damaging the paint (fresco) layer. For this reason, both Vitruvius (6) and Pliny (17) describe the preparation of lime for plasterwork to involve a thorough soaking or softening process (macerata). When referring to lime for structural use, however, Vitruvius uses the word extincta (II.5.1) instead of macerata. While extincta and macerata are both frequently interpreted as referring to slaking, Vitruvius’ change in diction points to a potentially different process.” (Science Advances “Hot mixing: Mechanistic insights into the durability of ancient Roman concrete”)

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