Contemporary concrete is designed to last for about 100 years. Yet at the bottom of the Mediterranean Sea lie the remains of Roman harbors, buildings and other structures that have remained surprisingly intact for almost 2000 years. What's the secret to their phenomenally durable concrete?
"The Romans developed a huge harbor infrastructure in the first century B.C. and first century A.D., and they built the harbors so well that they didn't need to keep repairing them," explained Marie Jackson, a researcher at the University of California, Berkeley's civil and environmental engineering department.
Jackson and several of her Berkeley colleagues, lead by civil engineering professor Paulo Monteiro, recently examined the underwater structures at Pozzuoli, an Italian seaside town on the Bay of Naples. These harbors were in use for centuries, long after the method of their construction was lost with the fall of Rome. The harbors are still in relatively good shape today, considering they've been subject to centuries of salt water and erosion.
But apparently, the salt water is part of the reason why Roman concrete lasts so long.
Like modern chemists, Roman builders took limestone and burned it to create lime, a key component of mortar. But then, Roman builders mixed the lime with volcanic ash from the Gulf of Naples in the Mediterranean Sea, and saturated the mixture with salt water.
The reaction between the volcanic ash, called pozzolan, and the salt water naturally produces a bonding material called calcium aluminum silicate hydrate.
"In a sense, what the Romans were doing is almost working with the salt water environment to create a material that actually remains durable for about the same time frame as rock," Jackson told.
Jillian SCHARR, What Ancient Roman Concrete Could Teach Modern Builders.
