By Mary Wortman

The Hard Truth About Concrete

Concrete Examples from the Past, Present, and Future

widen with time, and if water intrudes through structural fractures, the steel reinforcements inside can corrode and lead to collapse.

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Modern concrete has a durability problem that was not found in the mineral compound used by the ancient Ro- mans. Many of the structures (temples, aqueducts, and early roads) built more than 2,000 years ago still exist de- spite 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. Te ancient Romans used chemical reactions to harden their concrete. Tey used lime and volcanic rock to form mortar and then they introduced seawater. Te 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 Port- land cement. Portland cement was so named by Joseph Aspdin, who patented it in 1824, because the final prod- uct resembled the stone quarried on the Isle of Portland off the British coast. Portland cement does not incorpo- rate 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 re- pairs might be needed. Manufacturing Portland cement adds to the carbon dioxide that many industries release into the air.

So, the recipe from thousands of years ago was better than today. And, according to engineers and environmental- ists, the production of today’s concrete is bad for Mother Earth. Now what?

Two inventive microbiologists in the Netherlands believe they have the answer. Henk Jonkers and Eric Schlanger

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he hard truth about concrete is that it cracks. No matter how it is mixed or reinforced, it cracks. Eventually buildings begin to crum- ble, streets and sidewalks develop fissures that

are researchers at Delft Technical University who have created a self-healing concrete that could revolutionize the way the world builds. Tey have developed a con- crete that can self-regenerate. Te “living concrete” in- cludes a healing agent—bacteria.

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. Te result is something called “bioconcrete.” It is mixed just like regular concrete but uses an extra ingredient, the healing agent of bacteria. Te bacteria survive intact during mixing, dissolve and become active only if the concrete cracks and water gets in.

Te bacteria have to be able to remain dormant for years before being activated by water. Tey also has to stay alive in the dry environment of concrete. In addition, they must produce a strong viable repair material when they become 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. Tey 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. Ten they chose the bacillus bacterium, which creates calcite, commonly known as limestone. Te ancient Romans had the recipe right!

Te practical application of self-healing concrete may be only a few years in the future. Jonkers has indicated the production process is too expensive for immediate use in a commercial environment but early products can re- place the human factor in such hazardous repair jobs as nuclear waste containers.

From the Pantheon of Ancient Rome to Angel Stadium of Anaheim, it is clear that our reliance on concrete has not changed in thousands of years. Only the applica- tions and recipes have been updated.

This article was written and submitted by Mary Wortman of Cardinal Property Management, AAMC.

March / April 2017