"Back in 2023, we reported on MIT scientists' conclusion that the ancient Romans employed "hot mixing" with quicklime, among other strategies, to make their famous concrete, giving the material self-healing functionality. The only snag was that this didn't match the recipe as described in historical texts. Now the same team is back with a fresh analysis of samples collected from a recently discovered site that confirms the Romans did indeed use hot mixing, according to a new paper published in the journal Nature Communications."
"like today's Portland cement (a basic ingredient of modern concrete), ancient Roman concrete was basically a mix of a semi-liquid mortar and aggregate. Portland cement is typically made by heating limestone and clay (as well as sandstone, ash, chalk, and iron) in a kiln. The resulting clinker is then ground into a fine powder with just a touch of added gypsum to achieve a smooth, flat surface. But the aggregate used to make Roman concrete was made up of fist-sized pieces of stone or bricks."
New analysis of samples from a recently discovered Roman site confirms the use of hot mixing with quicklime in ancient Roman concrete, producing self-healing functionality. Ancient Roman concrete combined a semi-liquid mortar with fist-sized stone or brick aggregate rather than the powdered clinker used in modern Portland cement. Portland cement is produced by heating limestone and clay (with other minerals) to form clinker and grinding it with gypsum into a fine powder. Vitruvius recommended walls at least two feet thick built of squared red stone, brick, or lava bound with hydrated lime and volcanic tephra. Raman spectroscopy and multi-detector EDS enabled multiscale chemical profiling and phase mapping of Roman concrete samples.
Read at Ars Technica
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