Study: Seawater Reactions Strengthened Ancient Concrete

Samples from this ancient Roman pier in Italy were studied with x-rays at Berkeley Lab. Photo by J.P. Oleson.

A new look inside 2,000-year-old concrete—made from volcanic ash, calcium oxide (CaO) (also known as lime), and seawater—is helping explain the chemistry that has allowed ancient structures to withstand the test of time. The research is also inspiring a hunt for the original recipe so that modern concrete manufacturers can do as the Romans did.

Researchers at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) (Berkeley, California) used x-rays to study samples of Roman concrete from an ancient pier and breakwater sites at microscopic scales.

Their earlier work found that crystals of aluminous tobermorite, a layered mineral, could play a key role in strengthening concrete. Now, this study is piecing together how and where this mineral formed—namely, in the centers of partially dissolved relict lime clasts.

They believe the work could lead to concrete manufacturing techniques with less environmental impact than modern Portland cement processes. Also, researchers suggest a reformulated recipe for Roman concrete could be tested for applications on ocean-facing structures such as seawalls, and could help safeguard hazardous wastes.

According to Marie Jackson, a professor with University of Utah (Salt Lake City, Utah) who led the study, the CaO likely reacted with volcanic ash when it was exposed to seawater. “Contrary to the principles of modern cement-based concrete, the Romans created a rock-like concrete that thrives in open chemical exchange with seawater,” Jackson says.

The work featured participation by several global university researchers, and it was supported by the U.S. DOE’s Office of Science (Washington, DC) and the National Science Foundation (Arlington, Virginia).

Source: Berkeley Lab,