Researchers crack Roman concrete mystery

Abstract

Many Roman structures made from concrete, which include roads, aqueducts, ports and massive buildings, still remain some two millennia after they were first built.Rome's famous Pantheon, which has the world's largest unreinforced concrete dome and was dedicated in AD 128, is still intact, and some ancient Roman aqueducts still deliver water to Rome today. Despite this, modern concrete structures can start to crumble just a few decades after construction. Researchers have spent decades trying to figure out the secret of this ultradurable, ancient construction material, particularly in structures that endured especially harsh conditions, such as docks, sewers and seawalls, or those constructed in seismically active locations. Researchers from MIT, Harvard University, and laboratories in Italy and Switzerland have been discovering ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities. It was previously assumed that the durability of ancient concrete was due to pozzolanic material such as volcanic ash from the area of Pozzuoli, on the Bay of Naples. This specific kind of ash was shipped across the Roman empire to be used in construction, and was described as a key ingredient for concrete in accounts by architects and historians at the time. Under closer examination, these ancient samples contain small, distinctive, millimetre-scale bright white mineral features, which have been long recognised as a ubiquitous component of Roman concretes.