Concrete Examples from the Past, Present, and Future
The hard truth about concrete is that it cracks. No matter how it is mixed or reinforced, it cracks. Eventually buildings begin to crumble, streets and sidewalks develop fissures that widen with time, and if water intrudes through structural fractures, the steel reinforcements inside can corrode and lead to collapse.
Modern concrete has a durability problem that was not found in the mineral compound used by the ancient Romans. Many of the structures (temples, aqueducts, and early roads) built more than 2,000 years ago still exist despite earthquakes, invasions, and seawater.
Why do these millennia-old examples still exist, many intact, while we have a hard time getting our sidewalks to last more than 20 years? Part of the answer lies in the blending agents. The ancient Romans used chemical reactions to harden their cement. They used lime and volcanic rock to form mortar and then they introduced seawater. The seawater triggered a chemical reaction that hydrated the lime and reacted with the ash to “cement” everything together, resulting in an exceptionally strong product.
Today, the most common modern blend is called Portland cement. Portland cement was so named by Joseph Aspdin, who patented it in 1824, because the final product resembled the stone quarried on the Isle of Portland off the British coast. Portland cement does not incorporate the combination of volcanic ash and lime so it does not bind as well as the Roman version of concrete.
In use for more than 200 years, some Portland cement products have a service life of nearly 50 years before repairs might be needed. According to a research paper written by Paulo Monterro, a professor of civil and environmental engineering at the University of California, Berkeley, and the lead researcher of a team that is analyzing the Roman concrete, manufacturing Portland cement adds to the carbon dioxide that many industries releases into the air.
So, the recipe from thousands of years ago was better than today. And, according to engineers and environmentalists, the production of today’s cement is bad for Mother Earth. Now what?
Two inventive microbiologists in the Netherland believe they have the answer. Henk Jonkers and Eric Schlanger are researchers at Delft Technical University who have created a self-healing concrete that could revolutionize the way the world builds. They have developed a concrete that can self-regenerate. First highlighted on CNN in 2015, the “living concrete” includes a healing agent—bacteria.
In that CNN interview, Jonkers said he started working on the project in 2006 to crack the problem of the lack of durability and the not-so-eco-friendly manufacturing process used today. The result is something called ‘bioconcrete.” It is mixed just like regular concrete but uses an extra ingredient, the healing agent of bacteria. The bacteria survive intact during mixing and dissolves and becomes active only if the concrete cracks and water gets in.
Jonkers further explained to CNN in a March 2016 interview that the bacteria has to be able to remain dormant for years before being activated by water. It also has to stay alive in the dry environment of concrete. In addition, it must produce a strong viable repair material when it becomes activated. Jonkers’ team decided the repair material needed to be limestone. Remember the recipe the Romans used? A key ingredient was limestone. But the bacteria also have to eat to stay alive. They need a food source until called up for duty.
After trying sugar, which resulted in a soft product, the team introduced calcium lactate, a component of milk, as the nutrient. Then they chose the bacillus bacteria, which create calcite, commonly known as limestone. The ancient Romans had the recipe right!
The practical application of self-healing concrete may be only a few years in the future. Jonkers told CNN that the production process is too expensive for immediate use in a commercial environment but early products can replace the human factor in such hazardous repair jobs as nuclear waste containers.
From the Pantheon of Ancient Rome to Angel’s Stadium of Anaheim, it is clear that our reliance on cement has not changed in thousands of years. Only the applications and recipes have been updated.
The modern world is a wondrous place. We already have self-driving cars, and self-repairing concrete is not too far off. What could be next? Only our imaginations know.
“We are combining nature with construction materials.”
Henk Jonkers, Delft University
“China used more concrete from 2011 to 2013 than the United States did in the entire 20th century.”
Bill Gates, “Gatesnotes.”
Mary Wortman is the Director of Public Relations for Cardinal Property Management.
Reprinted with permission from O.C. View, January/February 2017 issue; copyright by CAI, Orange Country Regional Chapter, all rights reserved.