From The Foundations of Rome to Global Carbon Emissions Reduction
Does solution for over 5 percent of CO2 emissions lie in the 2000 year old concrete making technology from ancient Rome?
Scientists explain ancient Rome’s long-lasting concrete
Concrete is the second most consumed substance on Earth after water. Overall, humanity produces more than 10 billion tons, about 4 billion cubic meters of concrete and cement per year or about 1.3 tons for every person on the planet, more than any other material, including oil and coal. The consumption of concrete exceeds that of all other construction materials combined. The process of making modern cement and concrete has a heavy environmental penalty, being responsible for 5% or so of global emissions of CO2.
According to the IPCC (Intergovernmental Panel on Climate Change), Carbon Dioxide (CO2) emitted during the cement production process represents the most important source of global carbon dioxide emissions by an industrial process outside the energy sector. Most of the CO2 that is generated in the manufacture of these materials is a by-product in the production of clinker, in which limestone (CaCO3) is converted to lime (CaO). Each ton of of cement that is produced requires 4.7 million BTU of energy, or the equivalent of about 400 pounds of coal, and releases almost a ton of CO2.
Those of us who have been fortunate to experience the Colosseum, Pantheon, Diocletian Palace, and other Roman architectural gems come away awestruck that these structures from antiquity are still standing today and many of them still in use. Meanwhile, our sports stadiums and bridges here in the US seem to start deteriorating after several decades. To have the necessary strength, tensile in particular, reinforcements are embedded in modern Portland cement-based concrete. But steel corrodes quickly, and as a result, most of today’s’ reinforced steel structures are designed to last less than 100 years.
How is it that our our modern energy intensive process produces a material that fails to match the strength and longevity of the concrete that Romans manufactured over 2000 years ago? Moreover, the process that Romans used generated less heat and fewer emissions, without the need to draw upon large drinking water supplies. Could a greater understanding of the ancient Roman concrete production process lead to greener building materials? It certainly seems so based on studies led by Marie Jackson, first at UC Berkeley in 2013 and then at the University of Utah in 2017. Both investigations were conducted in conjunction with the Advanced Light Source at Lawrence Berkeley National Laboratory.
Roman Technology to the CO2 Emissions Rescue?
Roman concrete was made by mixing volcanic ash with lime and seawater to make a mortar, then adding chunks of volcanic ash and rock (the “aggregate”) to that mortar. This concrete was used to construct not only buildings but also massive marine structures like piers and breakwaters. Rather than eroding, particularly in the presence of seawater, Roman concrete over time gained strength from this exposure.
The Romans themselves were aware that this strengthening was occurring. In the first century CE, Pliny the Elder wrote that the Roman method of making cement resulted in a creation “that as soon as it comes into contact with the waves of the sea and is submerged becomes a single stone mass (fierem unum lapidem), impregnable to the waves and every day stronger.”
Modern Portland cement concrete also uses rock aggregate, but instead of volcanic rock, its main components are sand, gravel, and crushed stone. Jackson and her fellow researchers suspected that a material known as aluminous (Al) tobermorite, found widely in Roman concrete but not in modern recipes, was part of what gave Roman concrete some of its properties. The problem was, Al-tobermorite generally doesn’t form without high heat, and even then, only small quantities are typically created. We know that the pozzolanic reaction that the Romans used to make concrete did not generate temperatures nearly as hot as those that are necessary to create modern Portland cement and moreover, the reaction is short-lived.
So where did the aluminum tobermorite come from? Jackson and her colleagues at UC Berkeley and the University of Utah discovered that elements within the concrete continue to react with seawater making the concrete increasingly stronger over time. In particular, the seawater dissolves components of the volcanic ash, creating conditions for Al-tobermite and a second mineral, phillipsite, to continue to grow over time, thus reinforcing the concrete and preventing cracks from developing. “Contrary to the principles of modern cement-based concrete,” said lead author Marie Jackson, “the Romans created a rock-like concrete that thrives in open chemical exchange with seawater.”
I believe that these discoveries are so important that it could lead to more environmentally friendly building materials. There are some limiting factors that make the revival of the Roman approach very challenging. One is the lack of suitable volcanic rocks. The Romans were fortunate that the right materials were on their doorstep. Secondly, the precise mixture that the Romans followed is not known and may take years of experimentation to discover the correct formula. And for marine structures, sustaining reinforcing steel in salty environment poses a significant challenge.
Cement manufacturing and concrete pouring are not only energy and emissions intensive because of the extreme heat required to produce these materials, they also consume large quantities of water. To produce a cubic meter of concrete requires about 250 liters of water. Curing, cooling, and cleaning water adds another 250 liters or so per cubic meter to the tally. In most cases, drinking water is used. In all, the manufacture of 4 billion cubic meters of concrete requires about one cubic kilometer of water ( about 600,000 acre-feet). Or to visualize it better, about 400,000 Olympic size swimming pools of drinking water is wasted on making concrete every year. What if we could substitute drinking water with seawater to make concrete in coastal areas where most of the earth’s population lives? The savings could be significant in terms of both environmental impact and dollars saved.
Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions. Transporting and mixing cement with gravel, sand, and water, and subsequent chemical reactions during concrete hardening create additional CO2 emissions and significant water consumption.
The global construction industry is the single largest industry in the world and is expected to have revenues of $10.0 trillion in 2020. With this growth prediction, it pays off to look how cement and concrete production could be improved to reduce energy and water consumption, as well as emissions. More experimenting with Roman concrete is warranted.