Natural Pozzolan Association
The American Concrete Institute


The Romans 2000 years ago discovered some of these deposits surrounding Mount Vesuvius near a town called Pozzuoli, so they called the material “Pozzolan”. They found that pozzolan could improve the quality of concrete, so they used it to construct roads, aqueducts, and buildings. Many of these projects still stand, 23 centuries later. Pozzolan is still used in concrete today.

Some significant projects in the West in which concrete utilizing natural pozzolan in cement include:

•East Bay Municipal Wastewater Treatment Plant - California
•Palo Verde (Nuclear) Power Generating Plant - Arizona
•Pyramid Lake Powerhouse - California
•Rock Springs Wyoming Power Plant - Wyoming
•Redding Airport Runway - California
•Los Angeles Aqueduct - California
•Los Angeles Flood Control District - California
•Bonneville Dam - Oregon
•Golden Gate Bridge - California
•Piers of the San Francisco-Oakland Bay Bridge - California
•Virtually all concrete in the California State Water Project

Pozzolan has a miraculous ability to hold water. A quantity of Pozzolan will retain its weight in water. This ability to hold water makes Pozzolan critical in agriculture. While about 72% of the earth’s surface is covered by water, 97% of the water is salt or brackish water that cannot be used by plants, animals, people, or industry. Only 3% of the water is fresh and much of that is not in the right place or at the right time for mankind to avoid droughts and fresh water shortages. In the future high quality natural pozzolan has an important role to play in sustainable green construction. Natural pozzolan increases service life and reduces the net greenhouse gas emissions (GHG) and energy consumption for a cubic yard of concrete. For every ton of cement replaced by natural pozzolan, there is a net reduction of 0.86 tons of CO2 emissions. This means that every 21 ton truckload used is equivalent to taking three automobiles off the road. In addition, the heat saved is 4.29 million BTU’s/ton, which would heat the average home for more than a week.

Roman Concrete Pozzolana: An Empire Out of Earth

Credit: Jim H January 6, 2015 Archaeology

Roman concrete made from volcanic earth called Pozzolana built their megastructures.

Ancient Romans demonstrated great acumen in military strategy, imperial governance, and western culture. But, perhaps the most impressive and unprecedented skill they possessed was their ability to construct strong and magnificent buildings and infrastructure. Indeed, the Romans built some of the most recognizable and enduring structures in the world, like the Colosseum and the Pantheon. Evidently, they not only understood how to design a structure to make it last, but they also had an acute grasp of what materials to use. The primary material that proved to be the key factor in their building success was Roman concrete, which is called Pozzolana.

The Pantheon in Rome, Italy, was built using Roman concrete.

What is Pozzolana?

Pozzolana comes from a type of volcanic ash. Unlike other types of volcanic material, Pozzolana contains siliceous (silicon dioxide) and aluminous elements. This unique composition makes the ash react with other materials. Under the right conditions, this ash will bond with specific elements to create a type of cement. It is this cement that became the backbone of Roman civilization.

Natural Pozzolana (volcanic ash) deposits. Image credit: wikipedia

While volcanic materials are prevalent in various areas, Pozzolana is mainly from the area of Pozzuoli, Italy, as the name suggests. Ancient Greeks were probably the first to use volcanic material to generate concrete. And it was the Greeks who actually founded the areas of Pozzuoli and Naples. Evidence exists from Kameiros, Rhodes, that indicates ancient Greeks were already using volcanic ash for cement in 500-400 BC. However, the Romans refined the process of using Pozzolana by creating lime-based pastes to bind structures together. With this process, Pozzolana could be used to create sturdy buildings in addition to advanced underwater footings, due to its ability to harden under water.

Why Was Roman Concrete Special?

Because of its widespread usage throughout the Roman world, it is no surprise that Romans thoroughly documented the production of cement. One of the most reliable sources when it comes to the use of Pozzolana is from Vitruvius, who wrote about four distinct variations. He distinguished the variations by color and in what areas the Romans could find them throughout Italy.

No matter where they found the ash, their mixing process was fairly standardized throughout the Roman world. According to historic records, Pozzolana consisted of three ingredients. In addition to the volcanic ash, the Romans also added a lime paste and small rocks. The process of mixing these ingredients resembled the way builders create modern concrete. However, the unique combination of ingredients made Pozzolana unusually strong, even in comparison to modern blends. This unprecedented strength resulted from the unique chemical makeup of the concrete itself.

Building a Legacy

Ancient Romans loved Pozzolana, because it could harden under water. After all, construction on dry land was already fairly diversified by the Roman era. Pozzolana, however, expanded construction to include seaports and other waterways, thereby helping anchor the Roman Empire with ports along the Mediterranean Sea.

Caesarea is the earliest known example to have used underwater Roman concrete technology on such a large scale. Image Credit: James Cocks, Wiki Commons.

One of the best examples of this construction is at Caesarea Maritima. Today, Caesarea Maritima is an Israeli national park. The ruins were part of a port that the Roman constructed under the rule of Herod the Great. Although it is no longer a center of commerce as it once was, many of the structures are still visible. This includes an aqueduct and a theater. Most impressively, parts of the construction are visible underwater in the shallow waters with minimal erosion or damage.

Another good example of the longevity of Roman concrete exists at Cosa. At Cosa, Romans laid the piers underwater by using long tubes, which allowed the concrete to set without seawater getting into the mix. Although the area has degraded through time, the three piers still stand. Amazingly, the underwater portions are in remarkably good condition.


Many factors helped the Romans achieve immense societal success. However, one of their critical feats was their ability to build enduring architecture. In fact, at one time, it was said that all roads lead to Rome. Pozzolana and its unique building capabilities were a large part of how that was possible.

Unfortunately, much of the ancient knowledge and skill of using Roman concrete died along with the Roman Empire. However, modern builders still find uses for Pozzolana as our society seeks to build its own lasting legacy for the centuries to come.