It's the most common human-made material on earth, the second most consumed substance after water, and the veritable foundation of contemporary society. Despite all that, and the fact that modern concrete is by many measures an advanced building material, it pales in comparison to Roman concrete. For proof, simply compare today's version—which often shows degradation after 50 years—with concrete-based Roman monuments that still stand after two millenia. Even more impressive are underwater Roman structures that show little decay in the presence of harsh marine environments.
Scientists at the University of California, Berkeley have recently studied Roman marine concrete in order to reveal the ancient building material's secrets. Using a scanning electron microscope on samples excavated from a harbor outside Tuscany, they found evidence of the incredibly stable compound calcium-aluminum-silicate-hydrate (CASH). In addition, they also noted the development of a rare mineral called aluminum tobermorite (Al-tobermorite), which exhibits important mechanical properties.
"Roman concrete has remained coherent and well-consolidated for 2,000 years in aggressive maritime environments," said civil engineer Marie Jackson in a UC Berkeley press release. "It is one of the most durable construction materials on the planet, and that was no accident. Shipping was the lifeline of political, economic, and military stability for the Roman Empire, so constructing harbors that would last was critical."
In addition to Roman concrete's superior longevity, it is also less carbon-intensive than the contemporary variety—requiring only two-thirds of the amount of heat needed to make Portland cement. Although the Berkeley researchers speculate that the longer curing time for Roman concrete—as well as the need for volcanic ash—will limit its potential use today, they suggest that it might be resurrected for applications in regions with large volcanic deposits. If fully industrialized, Neo-Roman concrete might offset 40 percent of the Portland cement used today.
Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.