Berkeley team observes new binder mechanism, performance in Roman concrete

Sources: University of California, Berkeley; CP staff

Using the Advanced Light Source at Lawrence Berkeley National Laboratory and core samples from an ancient breakwater near Naples, Italy, a UC Berkeley research team has examined Roman concrete’s fine-scale structure and extraordinarily stable binding compound, calcium-aluminum-silicate hydrate.

The Berkeley Lab equipment has also led to the first experimental determination of a very rare hydrothermal mineral, aluminum tobermorite. “Roman concrete has remained coherent and well-consolidated for 2,000 years in aggressive maritime environments,” says UC Berkeley Civil and Environmental Engineering Research Engineer Marie Jackson, who as lead author describes team findings in June and October 2013 articles for the Journal of the American Ceramic Society and American Mineralogist, respectively. “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.” As the Empire and shipping declined, so did the need for seawater concrete. “You could also argue that the original structures were built so well that, once they were in place, they didn’t need to be replaced,” concludes Jackson, who along with the Italcementi Group-sponsored Roman Maritime Concrete Study sourced core specimens.

Roman concrete’s lime and volcanic ash binder formulation was described around 30 B.C. by Marcus Vitruvius Pollio, an engineer for Octavian, who became Emperor Augustus. Early practitioners packed their lime-ash mortar and rock chunks into wooden molds immersed in seawater, which became an integral part of the mix—the resulting structures immune to chloride ion exposure.

The UC Berkeley research aims to identify the potential for expanded use of lime, volcanic ash or ASTM C618 fly ash in concrete, potentially offsetting some of the carbon dioxide emissions associated with the high temperature milling of ASTM C150 portland cement. Lower processing temperatures equate to lime production at two-thirds the CO2 levels of portland cement; volcanic ash is being considered as an alternative to fly ash as market supply conditions allow or dictate.

The research began with funding from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, which has an abundance of potentially concrete-grade volcanic ash. After an initial partnership with UC Berkeley, Harvard University and U.S. Department of Energy Office of Science joined KAUST in the research. In addition to the Berkeley Lab’s Advanced Light Source, researchers deployed Berlin Electron Storage Ring Society for Synchrotron Radiation in their analyses.