The dome of Tempio di Venere e Roma, a temple dedicated to two goddesses and inaugurated by Emperor Hadrian in A.D. At that time, Augustus initiated an extensive citywide program to repair old monuments and erect new ones, and builders exclusively used volcanic ash from a deposit called Pozzolane Rosse, an ash flow that erupted 456,000 years ago from the Alban Hills volcano, 12 miles southeast of Rome. But builders got picky around the time Augustus became the first Roman emperor, in 27 B.C. In the earliest concretes, Romans mined ash from a variety of ancient volcanic deposits. But combining a mortar with an aggregate like brick to make concrete was likely a Roman invention, Perucchio says. Other ancient societies such as the Greeks probably also used lime-based mortars (in ancient China, sticky rice was added for increased strength).
The volcanic ash reacted with the lime paste to create a durable mortar that was combined with fist-size chunks of bricks or volcanic rocks called tuff, and then packed into place to form structures like walls or vaults.īy the beginning of the second century B.C., the Romans were already using this concrete in large-scale construction projects, suggesting their experimentation with the building material began even earlier. Next they mixed in volcanic ash-usually three parts volcanic ash to one part lime, according to the writings of Vitruvius, a first-century B.C. The formula for Roman concrete also starts with limestone: builders burned it to produce quicklime and then added water to create a paste. Modern concrete is a mix of a lime-based cement, water, sand and so-called aggregates such as fine gravel. That resistance, or durability against the elements, may be due to one of the concrete’s key ingredients: volcanic ash. “What this material is assumed to have is phenomenal resistance over time.” It’s approximately ten times weaker,” says Renato Perucchio, a mechanical engineer at the University of Rochester in New York. considerably weaker than modern concretes. Geologists, archaeologists and engineers are studying the properties of ancient Roman concrete to solve the mystery of its longevity. Yet structures like the Pantheon and the Colosseum have survived for centuries, often with little to no maintenance. They had a different formula, which resulted in a substance that was not as strong as the modern product. The Romans started making concrete more than 2,000 years ago, but it wasn’t quite like today’s concrete. 80, seated 50,000 and hosted gladiatorial games, ritual animal hunts, parades and executions.
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