Durable Roman Concrete Provides Inspiration For Green Engineering
April Flowers for redOrbit.com – Your Universe Online
An international team of geologists and engineers have found inspiration in ancient Rome for their quest to make a more durable and sustainable concrete. The massive concrete structures of the Romans have withstood the elements for more than 2,000 years, which the team examined with the Advanced Light Source at Lawrence Berkeley National Laboratory (Berkeley Lab).
The team was led by Paulo Monteiro, a UC Berkeley professor of civil and environmental engineering and faculty scientist at Berkeley Lab, and Marie Jackson, a Berkeley research engineer in civil and environmental engineering. They examined the fine-scale structure of Roman concrete, describing how the extraordinarily stable compound — calcium-aluminum-silicate-hydrate (C-A-S-H) — binds the material used to build some of the most enduring structures in Western civilization. The team used samples of Roman concrete taken from a breakwater in Pozzouli Bay, near Naples, Italy.
This findings, published in two papers appearing in the Journal of the American Ceramic Society and the American Mineralogist, could help improve the durability of modern concrete, which within 50 years often shows signs of degradation, particularly in ocean environments.
The manufacturing of Roman concrete leaves a smaller carbon footprint than modern manufacturing, as well. For example, the process to create Portland cement, a key ingredient in modern concrete, requires fossil fuels to burn calcium carbonate (limestone) and clays at about 1,450 degrees Celsius. This activity accounts for about seven percent of global carbon dioxide emissions. The lime needed for Roman concrete, in contrast, is much cleaner, requiring temperatures that are two-thirds of that required for making Portland cement.
“Roman concrete has remained coherent and well-consolidated for 2,000 years in aggressive maritime environments,” said Jackson. “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.”
Used in a wide variety of situations, the Roman building material of choice was concrete — from monuments such as the Pantheon in Rome as well as in wharves, breakwaters and other harbor structures. The team was particularly interested in how the underwater concrete used in Rome endured the unforgiving saltwater environment.
Around 30 BC, Roman author and architect Marcus Vitruvius Pollio described the recipe for the concrete used throughout the city. Vitruvius was an engineer for Octavian, who would later become Emperor Augustus. According to Vitruvius, the secret ingredient was volcanic ash, combined with lime to form mortar. The Romans packed this mortar and rock chunks into wooden molds immersed in seawater. They thereby harnessed saltwater and made it an integral part of the concrete, rather than trying to battle the marine elements.
In addition to Pollio´s volcanic ash, the team describes a very rare hydrothermal mineral called aluminum“¯tobermorite“¯(Al-tobermorite), which formed in the concrete. “Our study provided the first experimental determination of the mechanical properties of the mineral,” said Jackson.
If Roman concrete was so effective, why did its use decline? “¯“As the Roman Empire declined, and shipping declined, the need for the seawater concrete declined,” said Jackson. “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.”
Monteiro said that although Roman concrete is durable, it is unlikely to replace modern concrete because it is not ideal for construction where faster hardening is needed. However, the researchers are finding ways to apply their discoveries to the development of more earth-friendly and durable modern concrete.
The team is investigating whether volcanic ash would be a good, large-volume substitute in countries without easy access to fly ash, an industrial waste product from the burning of coal that is commonly used to produce modern, green concrete.
“There is not enough fly ash in this world to replace half of the Portland cement being used,” said“¯Monteiro. “Many countries don´t have fly ash, so the idea is to find alternative, local materials that will work, including the kind of volcanic ash that Romans used. Using these alternatives could replace 40 percent of the world´s demand for Portland cement.”