With cities wondering how to protect themselves as seas rise, engineers have looked to the past – specifically to Roman sea walls that still stand 15 centuries after the empire fell and seem to be stronger with time.
The secret: Romans’ recipe for concrete.
Today’s concrete relies on Portland cement, a mixture of limestone and clay. The Roman formula instead blended lime, volcanic ash, ground-up volcanic rock and seawater.
The volcanic materials in the Roman mix contained the minerals tobermorite and phillipsite. Materials scientists have found that when these minerals were exposed to seawater, they crystallized inside the concrete and expanded, hardening the blend as well as sealing any spaces where water could permeate.
Engineers are now at work to replicate and test the ancient concoction for possible commercial use.
TRENDPOST: Making Portland cement is estimated to account for about 5 percent of the world’s carbon emissions. Finding a low-tech way to make a stronger substitute could benefit air quality as well as the durability of new construction.