Ancient Romans provide lesson in making low-carbon concrete

19 December 2014

No visit to Rome is complete without a visit to the Pantheon, Trajan’s Markets, the Colosseum, or the other spectacular examples of ancient Roman concrete monuments that have stood the test of time and the elements for nearly two thousand years.

A key discovery to understanding the longevity and endurance of Roman architectural concrete has been made by an international and interdisciplinary collaboration of researchers using beams of X-rays at the Advanced Light Source (ALS) of the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab).

The study has gained an understanding of the manufacturing process behind low-carbon concrete that could be invaluable in the construction of the world’s future structures.
In the concrete walls of Trajan’s Markets, constructed around 110 CE, Roman volcanic ash-lime mortar binds cobble-sized fragments of tuff and brick. Through observing the mineralogical changes that took place in the curing of the mortar over a period of 180 days and comparing the results to 1,900-year-old samples of the original, the team discovered that a crystalline binding hydrate prevents microcracks from propagating.

The mortars that bind the concrete composites used to construct the structures of Imperial Rome are of keen scientific interest not just because of their unmatched resilience and durability, but also for the environmental advantages they offer.
Roman architectural mortar is a mixture of about 85% (by volume) volcanic ash, fresh water, and lime, which is calcined at much lower temperature than Portland cement. Coarse chunks of volcanic tuff and brick compose about 45 – 55% (by volume) of the concrete. The result is a significant reduction in carbon emissions.

Incorporating a substantial volumetric component of volcanic rock in the production of specialty concretes could greatly reduce the carbon emissions associated with their production also improve their durability and mechanical resistance over time.

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