Concrete Knowledge Part 4~

Modern Concrete Structures

Ever since Ransome developed the use of rebar, concrete has built all types of monumental buildings and infrastructure works. The Panama Canal, World War II bunkers, and the famed Sydney Opera House share a building material with some of the toughest — and most visionary — buildings in the world.

1889 – First reinforced concrete bridge – Alvord Lake Bridge, San Francisco

Alvord Lake Bridge was built in 1889 in San Francisco, CA. The first reinforced concrete bridge, it survived the 1906 San Francisco earthquake and others with no damage. It still exists today, more than 100 years after it was built.

1891 – First concrete street in America – Bellefontaine, Ohio

In 1891, a man named George Bartholomew built the first concrete street in America in Bellefontaine, Ohio. Today, pervious concrete is being advocated as the best, and most environmentally friendly, surface for streets.

1903 – First concrete high-rise – The Ingalls Building, Cincinnati

In Cincinnati in 1903, Ransome’s system made possible the first concrete high-rise, the 16-story Ingalls Building. That neck-breaking height made the skyscraper one of the great engineering feats of its time.

1899 – Vienne River Bridge

The Vienne River Bridge in Chatellerault, France, built in 1899, is one of the most famous reinforced concrete bridges in the world.

1908 – Concrete homes – Union, New Jersey – designed and built by Thomas Edison

The nation’s first concrete homes were designed and built in Union, New Jersey, by none other than Thomas Edison. These homes still exist today.

* 1913 – First Ready-Mix delivery – Baltimore

The first load of “ready-mix” was delivered in Baltimore. Having concrete mixed in one place (a central plant) and then delivered by truck for use at a job site was a revolution for the concrete industry.

* 1915 – Colored concrete – L.M. Scofield, the first company to produce color for concrete

Lynn Mason Scofield founded L.M. Scofield, the first company to produce color for concrete. Their products included color hardeners, color wax, integral color, sealers, and chemical stains.

* 1930 – Air-entraining agents – resistance to damage from freezing and thawing

In 1930, air-entraining agents were used for the first time in concrete to resist damage from freezing and thawing — a decided boon to cold-weather building practices across the United States and the world.

1936 – Hoover Dam – largest-scale concrete project ever completed at the time

The Hoover Dam is located on the border of Arizona and Nevada. Completed in 1936 to hold back the mighty Colorado River, the dam is made of 3.25 million cubic yards of concrete, with an additional 1.11 million used for its power plant and surrounding structures.

1956-1992 – The American interstate highway system

All of America’s roads in the interstate highway system are made of reinforced concrete.

1963 – Assembly Hall @ University of Illinois – first concrete sports dome

The first sports arena with a concrete dome was built on the campus of the University of Illinois at Urbana-Champaign in 1963. Known as Assembly Hall, the arena looks like a flying saucer and seats more than 16,000 in a perfect concrete circle.

* 1970’s – Fiber reinforcement – method to strengthen concrete

Fiber reinforcement, in which glass, carbon, steel, nylon, or other synthetic fibers are mixed into wet concrete before pouring, was introduced as a way to strengthen concrete. Fiber reinforcement can be used to strengthen buildings as well as outdoor features from driveways, slabs, and sidewalks to swimming pools, patios, and decks.

1992 – Tallest reinforced concrete building – Chicago

At 65 stories, the skyscraper at 311 South Wacker Drive in Chicago was the world’s tallest reinforced concrete building at the time it was built. The postmodern structure is known only by its street address.

The Future of Concrete?

* Modern era – Cut-rate production yields inferior concrete

Concrete was once thought to be the answer to the world’s building problems; it’s malleable when wet, strong and durable when dry, and cheap enough to build almost whatever you want.

The problem is, it’s not permanent. At least, it doesn’t stay intact and viable permanently (even though it doesn’t break down easily, either). Despite all its impressive tensile strength, modern concrete can only keep its integrity without major repairs or replacement for about a century, at best. Today’s reinforced concrete is no match for “Roman concrete.”

Especially if reinforced concrete is cheaply made — say, with an unbalanced mix, inferior ingredients, or a careless pour — it can begin to disintegrate from the inside. As it weathers, water gradually seeps in through tiny cracks and makes its way toward the steel in the middle. As the concrete surrounding it cures, the rebar oxidizes and can expand enough to crack the concrete it’s supposed to be supporting.

Saltwater is particularly harmful to rebar, as salt will corrode the steel within five decades. Repeated cycles of freeze and thaw also can create and expand cracks — especially on concrete roads. Spreading salt does indeed deter the formation of ice, but it works in tandem with moisture to harms the rebar just as much as if seawater were constantly washing across it.

* Future – Potential improvements for concrete maintenance and production

There are many emerging methods for improving concrete, including special treatments to prevent water from getting through to the steel. Other advancements respond to the increasing global attention being paid to sustainability: “Self-​healing” concrete contains bacteria that secrete limestone, resealing any cracks that occur. The mix for “self-​cleaning” concrete is infused with titanium dioxide, which breaks down smog, keeping the concrete sparkling white. Improved versions of this technology may even give us street surfaces that clean out the exhaust from cars.

Also, a recent report suggests that it’s possible for us to replicate the recipe for Roman concrete, (which, despite its lower tensile strength, exhibits unparalleled durability). Roman concrete is not just waterproof; it’s been found to actually become stronger when in contact with seawater. Scientists surmise that microscopic crystals grow in the ancient concrete when it’s submerged in water, making it even less vulnerable to weathering.

Though they still haven’t fully pieced together the lost recipe, researchers know that volcanic ash pozzolana was fundamental to the strength of ancient Roman concrete. A recently announced project will experiment with similar volcanic ash off the coast of California to try reverse-engineer the process that created the most durable concrete in history.

If this happens, the combination of Rome’s secret concrete recipe and modern rebar engineering techniques just might revolutionize the use of concrete — and the world’s infrastructure and architecture — all over again.