How did scientists rediscover the secret ingredient in ancient Roman concrete?

The answer

In January 2023, researchers at MIT, led by Admir Masic, published findings in Science Advances revealing that Roman concrete's extraordinary durability comes from "hot mixing" - incorporating quicklime directly into the wet concrete mix. This creates calcium-rich clasts (white chunks visible in ancient concrete) that were previously considered defects. When cracks form and water enters, these clasts dissolve and recrystallize as calcium carbonate, effectively self-healing the material. Roman structures like the Pantheon (built 125 CE) and marine harbor walls at Caesarea have survived millennia because of this property. Modern Portland cement, invented in 1824, lacks this self-healing capability, explaining why contemporary concrete degrades within 50–100 years.