The Rock Solid History of Concrete

Ransome’s technology would outlive him. Famed architect Frank Lloyd Wright paved the way for reinforced concrete’s use in modern architecture. Because concrete is poured into a mold, it can be formed into shapes that even the most skilled masons could never achieve.

Wright’s first concrete building was Unity Temple in Oak Park, Illinois. Working on a limited budget, the only design carved into the mold was a Mayan-inspired decoration along the top of the building. The concrete was poured into the mold and over the rebar very slowly and meticulously to ensure it would set smoothly. The construction took place from 1905 to 1908. Thanks to its use of reinforced concrete, Unity Temple is considered by many to be the world’s first modern building.

Wright would become the United States’ preeminent architect. He incorporated concrete into many of his designs, and in 1935 the material was used liberally in perhaps his most famous work: Fallingwater in Mill Run, Pennsylvania. Fallingwater would not have been possible without Ransome’s reinforced concrete. With several unsupported cantilevers, or projecting beams, only a material with incredibly high tensile strength would hold up. The idea behind Fallingwater was to seamlessly integrate humanity and nature, and Wright managed to do just that. The building is a U.S. National Historic Landmark and considered one of the greatest works of American architecture in history.

Frank Lloyd Wright’s Fallingwater within Bear Run Nature Reserve, Pennsylvania.

Richard T. Nowitz

Ever since Ransome developed the perfect rebar, concrete has been used to build all types of monumental buildings and infrastructure works. In 1891, a man named George Bartholomew built the first concrete street in Bellefontaine, Ohio. The Vienne River Bridge in Chatellerault, France, built in 1899, is one of the most famous reinforced concrete bridges in the world. Canals, like the Panama Canal, are also made of concrete. Factories, offices, and bunkers built during the World Wars all used concrete. The Hoover Dam, completed in 1936 to hold back the mighty Colorado River, contains 3.25 million cubic yards of concrete, with an additional 1.11 million used for the powerplant and surrounding structures. The American Interstate Highway System, which was built between 1956 and 1992, is also made of reinforced concrete. Some of the toughest buildings in the world rely on a concrete foundation. Others, like the Sydney Opera House, are considered symbols of their country.

And yet even now, in this 21st century concrete jungle, there may be ways to improve the famed gray building material.

The Future of Concrete

Rebar made the modern world possible. But in terms of longevity, reinforced concrete is no match for what the Romans used. Rebar oxidizes when the surrounding concrete cures. Over decades, it rusts. The rebar will expand enough to put cracks in the concrete. In general, modern concrete can last about a century without major repairs or replacement, according to Concrete Planet. The impressive tensile strength of many of our structures is only temporary, and maintaining them is costly. Unity Temple’s restoration, for example, was a $25 million enterprise.

Seawater is particularly harmful to rebar, as the salt will corrode the steel within just five decades. Water can seep in naturally as tiny holes and, eventually, small cracks form on a concrete structure. Freeze-and-thaw cycles leave cracks in concrete roads as well, and while spreading salt will deter ice formation, it harms the rebar just as seawater does. If only we could replicate the Roman concrete of Sebastos Harbor, concrete fit for the Pantheon, the house of the gods.

Drilling out a sample of an ancient Roman concrete structure in Portus Cosanus, Tuscany, in 2003.

J.P. Oleson

A recent report suggests it’s possible. We know the volcanic ash pozzolana was fundamental to the strength of ancient Roman concrete, though we still have not pieced together the full recipe. In July, researchers announced they would use similar volcanic ash off the coast of California in an attempt to solve the ancient mystery. The goal is to reverse-engineer the process that created the most durable concrete in history.

Roman concrete is not just waterproof—it actually strengthens when in contact with seawater. Microscopic crystals are thought to grow in the ancient concrete when submerged in water, making it perfect for structures like Sebastos Harbor of ancient Israel.

Roman concrete has a weaker tensile strength than rebar concrete, as one might imagine, but its ability to stand up to erosion and weathering is unparalleled. A combination of Rome’s secret concrete recipe and modern rebar engineering techniques could allow concrete to revolutionize infrastructure and architecture yet again.