Key To Ancient Concrete’s Longevity Revealed
Concrete created by the Romans has survived underwater for 2,000 years, putting modern structural lifespans to shame. Now Berkeley Lab engineers have cracked the chemical code to Roman concrete’s durability.
It was already known that Romans made their concrete by mixing hydrated lime and volcanic ash to form mortar, which they then combined with volcanic tuff to make the building material.
The researchers put a sample of the material that was part of an ancient underwater harbor into Berkeley’s Advanced Light Source. They found the cement in it differed significantly from the commonly used modern version—the Roman material contained aluminum, which contemporary cement doesn’t have, and less silicon. This created an “exceptionally stable binder” and crystals in the concrete that make it stiffer.
Their findings could yield high-performance concretes made with less energy than modern varieties that are useful for hazardous waste storage and other purposes.
Top Image: Drill core of volcanic ash-hydrated lime mortar from the ancient port of Baiae in Pozzuloi Bay. Yellowish inclusions are pumice, dark stony fragments are lava, gray areas consist of other volcanic crystalline materials and white spots are lime. Inset is a scanning electron microscope image of the special Al-tobermorite crystals that are key to the superior quality of Roman seawater concrete. Courtesy Berkeley Lab.