Ancient Roman breakwaters provide new ideas for green concrete production

An ancient Roman breakwater immersed in the depths of the Mediterranean Sea experienced 2,000 years of erosive seawater, and it is still not destroyed. What makes it so "powerful"? According to a report recently organized by the Physicist Organization Network, an international research team led by the US Department of Energy's Lawrence Berkeley National Laboratory conducted an in-depth study of its durability and discovered unexpectedly that the ancient Romans were able to produce concrete in the process of production. Reduce CO2 emissions and reduce environmental damage. So how did they do it?

The secret of marine concrete

Researchers from the University of California, Berkeley, the King Abdullah University of Technology in Saudi Arabia, and the Synchrotron Radiation Electronic Storage Rings, Berlin, used Berkeley's Advanced Light Source (ALS) beam and other experimental facilities to investigate Pozoli Bay. Concrete found in the sea, the ancient Romans made concrete, unlike the modern practice is mainly reflected in two key aspects.

First, Portland cement is a glue that binds concrete components together. Concrete using Portland cement is a compound containing calcium, silicates, and hydrates (CSH). Ancient Roman concrete produced a very different compound by adding aluminum and a small amount of silicon. The calcium aluminosilicate hydrate (CASH) thus formed is a very stable binder.

Through the spectral identification of the ALS beamline, researchers believe that the specific way that aluminum replaces silicon in CASH may be the key to seawater concrete's cohesion and stability.

Another highlight relates to the hydration products of concrete. In theory, in concrete made of Portland cement, CSH is similar to a combination of naturally occurring layered minerals, known as xonotlite and xonotlite. Unfortunately, these ideal crystal structures have nowhere to be found in modern, common concrete.

However, xonotlite appears in the mortar of ancient seawater concrete. The researchers measured their mechanical properties under the beam line of the ALS high-pressure X-ray diffraction experiment, and for the first time elucidated the role of aluminum in its lattice: Alumilite has greater rigidity than low-crystalline CASH.

How did the ancient Romans do it?

Concrete, which is still the main building material of today, has caused increasing environmental problems in the production process. Its main component cement will emit large amounts of carbon dioxide during the production process. According to calculations, the amount of carbon dioxide emitted by the world's cement industry accounts for 7% of global greenhouse gas emissions. This does not include the secondary pollution of cement and concrete in the course of logistics and transportation. Cement and concrete building materials have become one of the main culprits of atmospheric pollution such as haze.

“This is not to say that modern production of concrete is not good. It is so good that we use 19 billion tons of production each year. The problem is that the carbon dioxide emitted from the production of portland cement accounts for 7% of the industry's emissions.” University of California, Berkeley Professor Paul Monteiro, a professor of civil and environmental engineering at the school.

Portland cement is the source of “glue”, which can bond the most modern concrete, but it needs to heat the mixed limestone and clay to 1450°C. After the limestone is heated, it will release a lot of carbon dioxide into the atmosphere.

The research team found that by identifying ancient Roman samples of offshore concrete, the Romans used less lime to produce Portland cement, and baked limestone at 900°C or lower and consumed much less fuel.

Analysis shows that Roman recipes require less than 10% lime by weight and that producing Portland cement can be less than 2/3 or less of the current temperature. Lime reacts with aluminum-rich pozzolans to form highly stable CASH and aluminosilicates, ensuring their strength and longevity.

Provide green high-performance models

“In the middle of the 20th century, the design of concrete structures lasted for 50 years. Many of them exceeded the scheduled time. Contemporary design buildings can last between 100 and 120 years. However, the facilities of the Roman port have experienced more than 2,000 years of chemistry. Erosion and underwater waves still survived," Monteiro said.

The main disadvantages of modern concrete as an engineering material are low tensile strength, poor deformability, and easy cracking. In the future of urban development and infrastructure construction, durable and low-carbon concrete is urgently needed.

The description of the use of volcanic ash started from ancient times. The first was Vitruvius, an engineer of Emperor Augustus. It was later reported that the best offshore concrete was a volcanic area from the Gulf of Naples. These ashes have similar mineral properties, called pozzolanic cement, and can be found in many parts of the world.

The ancient Romans mixed volcanic ash in nature when making their unique concrete. They mixed lime and volcanic ash to form a mortar, while mortar and volcanic tuffs were stuffed into a wooden lattice. Put it into seawater and trigger a thermochemical reaction instantly. Hydrated lime incorporates water molecules into its structure and reacts with pozzolan cement.

Monteiro said: "For us, volcanic ash is important in its practical application. The more powerful, more durable modern concrete can use less fuel and less carbon to release into the atmosphere, which is more in-depth Learn the valuable lessons learned by the Romans on how to create unsurpassed concrete."

Green high-performance concrete carries people's hopes. At the same time, it also made people realize that the future development of concrete not only meets the needs of building functions, but also needs to consider the impact on the environment to a large extent. The mutual integration of architecture and the environment can better reflect the beauty of the building, and it can also make the environment where people live more comfortable. Undoubtedly, the new findings of the study provide a model of concrete strength and toughness for the future. The materials and methods used in ancient Rome provide useful reference for the future production of green high-performance concrete. (Reporter Hualing)